DISCARDING TOMATO JUICE
It was formerly customary, and is still the practice of some manufacturers of tomato pulp, to discard a portion of the juice of the tomatoes. Some manufacturers, especially in the preparation of pulp from tomato trimmings, allow the trimmings to pass over a colander and thus separate the free juice, which is discarded. Others allow the product of the cyclone to stand for a time in tanks and then discard the clear juice which settles in the bottom of the tanks. Both practices are wasteful and have generally been discontinued. Some still adhere to one or both, however, and it was thought best to make the matter the subject of study.
Some discard the juice because of the belief that it consists of nothing but water and is valueless. Some are of the impression that the juice separated from the trimming stock before straining takes on a brown color during evaporation which would interfere with the red color desired in the finished product, if allowed to go into the pulp. Some recognize the value of the juice, but believe that the expense of its evaporation would not be warranted by the increased quantity of pulp. Some have not measured the juice discarded and greatly underestimate its volume.
With the view of determining the approximate value of the material discarded in this manner, a batch of material, fresh from the cyclone, was divided into two portions, one of which was immediately concentrated to form a pulp, and the other was allowed to stand about 20 minutes when a clear liquor had separated at the bottom. This clear liquor was then removed and the remainder evaporated until the desired consistency was obtained.
Samples of the finished pulps, of the raw product from which each was prepared and of the clear liquor, separated from the second one, were preserved by sealing in cans and processing. These samples were numbered as follows:
- 702—Product from the trough under the second cyclone, or finisher.
- 703—Clear liquor, which separated at the bottom of the tank, after a portion of 702 was allowed to stand. This formed about one-fourth of the entire product of the tank.
- 704—Drained residue from 703.
- 705—Finished pulp obtained by concentrating 704.
- 706—Finished pulp obtained by concentrating 702.
These samples were examined with the results given below.
Table 1.—Composition of Pulp and of the Liquor Separated from It
| Sample Number | Total Solids | Insoluble Solids | Ash | Sugar (as Invert) | Acid(as Citric) | Undetermined Organic Matter |
| Per Cent | Per Cent | Per Cent | Per Cent | Per Cent | Per Cent | |
| 702 | 4.38 | 0.40 | 0.34 | 2.27 | 0.29 | 0.87 |
| 703 | 3.84 | 0.10 | 0.38 | 2.32 | 0.29 | 0.75 |
| 704 | 4.47 | 0.50 | 0.38 | 2.31 | 0.31 | 0.77 |
| 705 | 9.17 | 1.83 | 0.78 | 4.07 | 0.51 | 1.87 |
| 706 | 7.85 | 0.98 | 0.69 | 3.51 | 0.46 | 2.04 |
The two products (705 and 706) were evaporated under exactly the same conditions and to what appeared to the operator to be the same consistency. After cooling, however, it was apparent that while the body of the two finished products was apparently equal, the consistency of No. 706 was superior to No. 705 in that the former was smooth and creamy, whereas the latter had a somewhat irregular, lumpy appearance. This difference was doubtless due to the greater content of soluble solids in No. 706. The color of the two samples was identical.
A mixture of one part of No. 703 and three parts of No. 704 when evaporated in the laboratory to the same consistency was identical in every way with No. 706.
From the composition as stated in [Table 1] it is apparent that the flavor and food value of the clear juice, which is sometimes discarded (represented in No. 703), are practically identical with the unconcentrated pulp as it passes through the cyclone. In fact, the only difference between the two appears to be about one-half per cent of insoluble matter. When the product is allowed to separate, it seems probable that this insoluble material as it rises in the mass has a tendency to act like a filter and carry up with it a large proportion of the bacteria and moulds present.
The scale on which the work was done did not permit of sufficiently accurate measurement of the finished pulp to warrant the calculation of the loss in quantity caused by discarding the juice. From the composition of the pulps and of the raw material, however, it is apparent that this loss is practically proportional to the percentage of juice discarded.
It is apparent, therefore, that the evaporation of the material just as it passes through the finisher will yield a product of the same color, of better consistency, in considerably greater quantity, and at practically the same proportionate expense of concentration as the evaporation of the residue after discarding the juice in accordance with the custom mentioned above.
COMPOSITION OF TOMATO PULP[1]
Whole Tomato Pulp
The results obtained by the examination of 33 samples of whole tomato pulp are given in [Table 2]. The concentration of the samples varies from unconcentrated pulp as it runs from the cyclone to pulps of very heavy consistency. This table contains the data from which Tables 4 and 5 were calculated, although during the season a partial analysis was made of a large number of other samples, and the data secured therefrom were in all respects confirmatory of the relations calculated from [Table 2].
In addition to the data obtained by the various determinations, [Table 2] gives the relation between the results of the determinations for each individual sample. For instance, the ratio of pulp solids to filtrate solids (pulp solids divided by filtrate solids) varies in the different samples from 1.091 to 1.154, and, with the exception of two samples, it varies from 1.100 to 1.145. The average of the 33 samples was 1.12. The relation of insoluble solids to total solids (expressed as per cent of insoluble solids in total solids) is shown in Table 2. Considering the variations in the methods employed by different manufacturers in the preparation of tomato pulp, the per cent of insoluble solids in the total solids as shown by this column is closer than we might expect, varying in most of the samples from 11 to 14 per cent.
The per cent of sugar in the soluble solids, as shown by Table 2, varies in most of the samples from 50 to 55 per cent. This figure cannot be expected to be constant in different localities and in different years.
The acid, estimated as citric, constitutes in most of the samples from 9 to 10 per cent of the soluble solids.
Of especial interest is the refractive constant of the filtered liquor, shown in the last column of Table 2. The refractive constant of the various samples is much more uniform than might be expected from a product of this nature.
[Table 2] is chiefly interesting as affording the data from which [Tables 4] and [5] were calculated. The uniformity of the relations shown in [Table 5] is such that it is usually possible from one determination on the filtrate and the determination of solids in the pulp by drying to distinguish pulp made from whole tomatoes from that made from trimming stock. For instance, if the specific gravity or index of refraction of a filtrate prepared from a pulp of unknown origin, and the per cent of solids in the pulp by drying, do not agree approximately with the relation between these determinations as shown in [Table 5], it may be assumed that the sample was not prepared from whole tomatoes, or that some other substance, such as salt, has been added. Moreover, trimming stock pulp rarely conforms to the relations found in whole tomato pulp. For instance, the insoluble solids are usually higher and the acid lower in trimming stock pulp.
Trimming Stock Pulp
In [Table 3] are given the results of the examination of 21 typical samples of trimming stock pulp prepared at different plants and in different localities. This table is of especial interest in showing that the relations between the results of the various analytical determinations differ from those of whole tomato pulps as given in [Table 5]. For instance, in No. 1470 the immersion refractometer reading is 45.90, and the per cent of solids is 9.54, whereas, according to [Table 5], the per cent of solids in the pulp corresponding to an index of refraction of 45.90 should be 8.57. The specific gravity of the pulp is 1.0373, which, according to [Table 5], should correspond to 8.98 instead of 9.54. Of course it cannot be said definitely that a pulp which on examination is found to conform to all the relations shown in Table 5 is necessarily whole tomato pulp. It is entirely possible for an occasional sample of trimming stock pulp to conform to all the relations shown in that table; moreover, the extent to which different samples of trimming stock pulp will vary from the relations shown in [Table 5] differs with the manner of preparation. For instance, if a portion of the juice is discarded in the manufacture of trimming stock pulp, as is still the practice of some manufacturers, the variation from whole tomato pulp will be greater than otherwise and the variation will increase with the amount of juice discarded.
Methods of Analysis [2]
These methods may also be applied to the examination of raw tomatoes and canned tomatoes. In applying the relations given below to the results obtained by the examination of tomato pulp or canned tomatoes, it is assumed that no substance such as sugar or salt has been added. If salt is found to be present in excess of the amount normal to tomatoes (from 0.05 to 0.1 per cent), it is necessary to determine the amount and make correction therefor before applying the relations given below.
In examining raw tomatoes, care must be taken to secure a representative sample of the juice. This cannot be done by applying pressure directly, as the juice of the seed receptacles is of different composition from that of the fleshy part of the tomato. It is necessary, therefore, to crush the sample and thoroughly cook it in a flask surrounded by boiling water and connected with a reflux condenser.
Microscopic Examination
The laboratory of the National Canners’ Association is frequently asked to examine samples of tomato products to determine whether or not they comply with the Government requirements. In examining these samples we use the Government method (the Howard method), but do not participate in the discussions regarding its merits and shortcomings.
It is our experience that skilled analysts can check themselves and each other with reasonable accuracy, and it is our duty to tell the manufacturer whether his product is legal. Should the Bureau of Chemistry adopt some other method as preferable to the Howard method, it would be our duty to use the new method and continue to serve the industry by telling the manufacturer whether samples submitted by him would pass the Government tests.
With a full understanding of our attitude in this matter many manufacturers of tomato products send samples from time to time for examination. It is made plain in every instance that the results obtained by the examination of a particular sample refer only to the batch from which that sample was taken and may give no indication of the character of any other batch.
Some manufacturers of tomato products use the Howard method as a check on their factory control. For this purpose it is not satisfactory to have samples examined in a laboratory located at a distance from the factory. Even if several samples are examined from a day’s run, they probably do not represent all the pulp manufactured on that day. It sometimes happens that one wagonload of tomatoes is almost entirely free of rotting material, whereas the succeeding load contains a considerable amount. Even with inefficient sorting, the pulp made from the first load will show a low microscopic count whereas, unless sorting is exceptionally good, the pulp made from the second load may show a high count. Thus one batch may readily comply with the requirements of the Bureau of Chemistry and the next batch may be outside of those limits. Because of this fact this laboratory recommends that manufacturers of tomato pulp do not rely upon the microscopic results of a single sample. The only way in which the product may be absolutely controlled by means of the microscopic count is to examine a sample from each batch—that is, from each kettleful or tankful that is evaporated. This is manifestly impossible. It would require several analysts for one plant. Moreover, it is entirely unnecessary.
It has been found that much better results can be secured by having an analyst in the plant to examine samples from time to time. Then, whenever the microscopic count becomes excessive, he can locate the trouble and see that it is corrected.
Manufacturers who desire frequent analyses of their products, therefore, should employ an analyst and arrange to have him instructed in a laboratory conversant with the Howard method as used by the Government. The laboratory of the National Canners’ Association makes it a practice to give the necessary instruction in this method to analysts employed by members of the association. These analysts should be carefully selected. Other things being equal, better results should be expected of a college graduate or at least one who has had college training in biology and chemistry. It has been repeatedly demonstrated, however, that a carefully selected man or woman with common school education can learn the method and use it with sufficient accuracy for factory control. The person selected for this work should have good powers of observation and a positive character.
This laboratory has heretofore advised that manufacturers of tomato pulp should not give too much attention to the microscopic count of their product. We have maintained that the expense would be better placed on the sorting belt; that if the sorting and trimming were adequately done, the plant maintained in a sanitary condition and the product manufactured as rapidly as possible, a low microscopic count would be assured. This we still maintain is true. So many cases have come to our attention, however, in which canners have not succeeded in maintaining the degree of sorting necessary with a product of this kind that we have grown to feel that the presence of an analyst working continuously in a plant is an additional safeguard.
The conditions attending the canning of tomatoes are widely different from those attending the manufacture of tomato pulp. The ordinary rot is almost always apparent from the outside of the tomatoes[3] and is removed by the peelers when preparing tomatoes for canning. Practically none of it, therefore, finds its way into the can. With pulp it is quite different. Any rot which is not removed by sorting and trimming goes into the cyclone and passes into the pulp. With trimming stock pulp, the condition is obviously much worse than with whole tomato pulp. One hundred pounds of tomatoes will yield not far from 85 pounds of cyclone juice. If only trimming stock is made into pulp, however, nearly half the tomatoes are used for canning and the remainder (50 or 55 pounds of trimming stock) will only make something like 35 or 40 pounds of cyclone juice. Yet, since the rot is almost entirely on the outside of the tomatoes, this 35 or 40 pounds made from the trimming stock contains the same amount of molds as the 85 pounds manufactured from the whole tomatoes. The mold count of the trimming stock pulp, therefore, is much higher than that of whole tomato pulp made from the same raw product.
The Bureau of Chemistry condemns tomato pulp whose microscopic examination gives results as high as the following figures:
| Molds | 66 per cent of fields. |
| Bacteria | 100 million per cubic centimeter. |
| Yeasts and spores | 125 per 1/60 cubic millimeter. |
These figures, of course, apply to the Howard method as employed by the Bureau of Chemistry. The method is entirely arbitrary and results agreeing with those obtained by the Bureau of Chemistry can be obtained only by using this method substantially as it is used by the bureau. An examination of the pulp, therefore, by an analyst who is not thoroughly conversant with this method as it is employed by the Bureau of Chemistry not only is useless but may actually afford a manufacturer a false sense of security which will be greatly to his disadvantage.
Microscopic Equipment Required
The apparatus employed by the Bureau of Chemistry includes apochromatic objectives and compensating oculars. In 1914 it became impossible to obtain these accessories[4] because of the European war and equivalent apparatus of American manufacture was found to give the same results. Both of these forms of apparatus are recognized in the official Howard method which is given below.
This laboratory made a careful study of the accessories available in order to determine what could best be used. It was found that very satisfactory results could be obtained by employing a 10X Huyghenian ocular and a 4 mm. achromatic objective (working distance 0.6 mm.) and a 16 mm. achromatic objective. These accessories require a careful adjustment of light, but with proper use enable an analyst to secure satisfactory results. It is found that the best results are obtained with a rather dark field.
The apparatus necessary for the Howard method, including the accessories mentioned above, may be obtained of two American manufacturers, the Bausch & Lomb Optical Company, of Rochester, N. Y., and the Spencer Lens Company, of Buffalo, N. Y.
There is given below a full list of the optical apparatus required, including catalog numbers of the two manufacturers, as far as numbers have been assigned by them to the various items. In addition to the apparatus given in this list, the analyst should have a 50 c. c. graduated cylinder for measuring and diluting samples. This may be obtained of any dealer in chemical apparatus and at many drug stores. When ordering the optical apparatus the full description as given below should be included.
Optical Apparatus for the Howard Method
| Quantity desired | Item | Bausch & Lomb | Spencer |
| 1 | Microscope without oculars, objectives or other accessories | FF | 44 |
| 1 | Abbe condenser with two iris diaphragms (lower and upper) | 1740 | 300 |
| 1 | Double nosepiece | 1844 | 450 |
| 1 | 16 mm. achromatic objective | 1021 | 108 |
| 1 | 4 mm. achromatic objective with working distance of 0.6 mm. | 1029 | 116 |
| 1 | 8 mm. achromatic objective with working distance of 1.6 mm. | 1027 | 112 |
| 1 | 10X Huyghenian ocular | 1104 | 142 |
| 1 | Mechanical stage | 2116 | 485 |
| 1 | Substage lamp with Daylite glass | 1774 | 385-B |
| 1 | Blood counting chamber (Haemacytometer with ruling of Thoma, Neubauer, Jappert, Brewer or Turk) | 3550 | 1472 |
| 6 | Cover glasses for same, 20×21 mm., 0.4 thick | 3595 | 1460 |
| 1 | Howard’s mold counting chamber (with ¾ inch inner disk) for same | 3566 | Special |
| 6 | Cover glasses for same 33 mm. square, 0.6 mm. thick | 3598 | Special |
| 2 | Cases for counting chambers | 3580 | 1505 |
All analysts undertaking the Howard method should secure copies of the two bulletins of the United States Department of Agriculture written by Mr. B. J. Howard—Bulletin 569 on Sanitary Control of Tomato Canning Factories and Bulletin 581, Microscopic Studies on Tomato Products. These bulletins may be obtained from the Superintendent of Documents, Government Printing Office, Washington, D. C., on payment of five cents each in coin.
The details of the method as given below are reprinted from the Methods of Analysis of the Official Agricultural Chemists as amended in 1921.
Apparatus
(a) Compound microscope.—Equipped with apochromatic objectives and compensating oculars, giving magnifications of approximately 90, 180, and 500 diameters. These magnifications can be obtained by the use of 16 and 8 mm. Zeiss apochromatic objectives with X6 and X18 Zeiss compensating oculars, or their equivalents, such as the Spencer 16 and 8 mm. apochromatic objectives[5] with Spencer X10 and X20 compensating oculars, the draw-tube of the microscope being adjusted as directed below.
(b) Thoma-Zeiss blood counting cell.[6a]
(c) Howard mold counting cell.—Constructed like a blood-counting cell but with the inner disk (which need not be ruled) about 19 mm. in diameter.[6b]
Molds.—Tentative
Clean the special Howard cell so that Newton’s rings are produced between the slide and the cover-glass. Remove the cover and place, by means of a knife blade or scalpel, a small drop of the sample upon the central disk; spread the drop evenly over the disk and cover with the cover-glass so as to give an even spread to the material. It is of the utmost importance that the drop be mixed thoroughly and spread evenly; otherwise the insoluble matter, and consequently the molds, are most abundant at the center of the drop. Squeezing out of the more liquid portions around the margin must be avoided. In a satisfactory mount Newton’s rings should be apparent when finally mounted and none of the liquid should be drawn across the moat and under the cover-glass.
Place the slide under the microscope and examine with a magnification of about 90 diameters and with such adjustment that each field of view covers 1.5 sq. mm. This area is of vital importance and may be obtained by adjusting the draw-tube in such a way that the diameter of the field becomes 1.382 mm. as determined by measurement with a stage micrometer.[7] A 16 mm. Zeiss apochromatic objective with a Zeiss X6 compensating ocular or a Spencer 16 mm. apochromatic objective with a Spencer X10 compensating ocular, or their equivalents, shall be used to obtain this magnification. Under these conditions the amount of liquid examined is .15 cmm. per field. Observe each field as to the presence or absence of mold filaments and note the result as positive or negative. Examine at least 50 fields, prepared from two or more mounts. No field should be considered positive unless the aggregate length of the filaments present exceeds approximately one-sixth of the diameter of the field. Calculate the proportion of positive fields from the results of the examination of all the observed fields and report as percentage of fields containing mold filaments.
Yeasts and Spores.—Tentative
Fill a graduated cylinder with water to the 20 cc. mark, and then add the sample till the level of the mixture reaches the 30 cc. mark. Close the graduate, or pour the contents into an Erlenmeyer flask, and shake the mixture vigorously for 15 to 20 seconds. To facilitate thorough mixing the mixture should not fill more than three-fourths of the container in which the shaking is performed. For tomato sauce or pastes, or products running very high in the number of organisms, or of heavy consistency, 80 cc. of water should be used with 10 cc. or 10 grams of the sample. In the case of exceptionally thick or dry pastes, it may be necessary to make an even greater dilution.
Pour the mixture into a beaker. Thoroughly clean the Thoma-Zeiss counting cell so as to give good Newton’s rings. Stir thoroughly the contents of the beaker with a scalpel or knife blade, and then, after allowing to stand 3 to 5 seconds, remove a small drop and place upon the central disk of the Thoma-Zeiss counting cell and cover immediately with the cover-glass, observing the same precautions in mounting the sample as given under 28.[8] Allow the slide to stand not less than 10 minutes before beginning to make the count. Make the count with a magnification of about 180 diameters to obtain which the following combination, or their equivalents, should be employed: 8 mm. Zeiss apochromatic objective with X6 Zeiss compensating ocular, or an 8 mm. Spencer apochromatic objective with X10 Spencer compensating ocular with draw-tube not extended.
Count the number of yeasts and spores[9] on one-half of the ruled squares on the disk (this amounts to counting the number in 8 of the blocks, each of which contains 25 of the small ruled squares). The total number thus obtained equals the number of organisms in 1/60,000 cc. if a dilution of 1 part of the sample with 2 parts of water is used. If a dilution of 1 part of the sample with 8 parts of water is used the number must be multiplied by 3. In making the counts, the analyst should avoid counting an organism twice when it rests on a boundary line between two adjacent squares.
Bacteria.—Tentative
Estimate the number of rod-shaped bacteria from the mounted sample used in 29[10] (yeasts and spores), but before examination allow the sample to stand not less than 15 minutes after mounting. Employ a magnification of about 500, which may be obtained by the use of an 8 mm. Zeiss apochromatic objective with X18 Zeiss compensating ocular with draw-tube not extended, or an 8 mm. Spencer apochromatic objective with X20 Spencer compensating ocular and a tube length of 190, or their equivalents.[11]
Count and record the number of bacteria having a length greater than one and one-half times their width in an area consisting of five of the small size squares. Count five such areas, preferably one from near each corner of the ruled portion of the slide and one from near the center. Determine the total number of the rod-shaped bacteria per area in the five areas and multiply by 480,000. This gives the number of this type of bacteria per cc. If a dilution of 1 part of the sample with 8 parts of water instead of 1 part of the sample with 2 parts of water is used in making up the sample, then the total count obtained as above must be multiplied by 1,440,000. Omit the micrococcus type of bacteria in making the count. Thus far it has proved impracticable to count the micrococci present, as they are likely to be confused with other bodies frequently present in such products.
Determination of Total Solids
1. BY THE EXAMINATION OF THE PULP
The total solids in tomato pulp may be determined by drying in vacuo at 70° C.; by drying at atmospheric pressure at the temperature of boiling water; by calculation from the specific gravity of the pulp; or from the per cent of solids, specific gravity or index of refraction of the filtrate. The solids obtained by different methods on 31 samples of pulp are given in [Table 4].
(a) By drying.—By drying either in vacuo or at atmospheric pressure, it is our experience that after the sample has reached apparent dryness, four hours’ drying gives complete results. From 2 to 4 grams should be taken for the determination, and enough water added to distribute the sample uniformly over the bottom of a flat-bottomed dish at least 2.5 inches in diameter.
The solids as determined by drying in vacuo at 70° C. are about 108.5 per cent of the result obtained by drying at the temperature of boiling water at atmospheric pressure. This figure is the average of the results obtained by the examination of 20 samples of pulp, in all of which the per cent of solids obtained by drying in vacuo agree quite closely with the per cent obtained by drying at atmospheric pressure multiplied by 1.085. In 15 of the 20 samples examined, the difference did not exceed 0.10 per cent, and in only one case did it exceed 0.20 per cent. The results obtained by the subsequent examination of a considerable number of other samples confirm this relation.
(b) By calculation from the specific gravity of the pulp.—There is a very exact relation between the specific gravity of pulp (determined by the method given above) and the per cent of total solids as determined by drying. The solids corresponding to pulps of various specific gravities are given in [Table 5], or may be obtained from the following formula which is derived from the same table:
Per cent Solids = 228 (sp. gr. of pulp - 1.000) + 19.1 (sp. gr. of pulp - 1.015).
2. BY THE EXAMINATION OF THE FILTRATE
If a sample of pulp of considerable size be thrown on a folded filter, a filtrate is obtained whose composition has a definite relation to that of the whole pulp.
(a) By drying.—The per cent of solids in the filtrate may be determined by drying in vacuo at 70° C, or under atmospheric pressure at the temperature of boiling water.
As in the case of the drying of pulp, a constant relation is found to exist between the per cent of solids in the filtered liquor as determined by drying in vacuo at 70° C., and the per cent of solids as determined by drying at atmospheric pressure at the temperature of boiling water. The per cent of solids in the filtrate obtained by drying at atmospheric pressure, multiplied by 1.125, gives the per cent of solids obtained by drying in vacuo. This relation is shown in detail in [Table 5].
Table 2.—Composition of Whole Tomato Pulps
| Sample No. | Composition of pulps | ||
| Sp. gr. at 20° C. | Total solids(a) | Insoluble solids | |
| _Per cent_ | _Per cent_ | ||
| 1290 | 1.0252 | 5.94 | 0.66 |
| 1291 | 1.0273 | 6.54 | 0.78 |
| 1292 | 1.0234 | 5.50 | 0.80 |
| 1293 | 1.0293 | 7.02 | 0.74 |
| 1294 | 1.0272 | 6.48 | 0.69 |
| 1295 | 1.0361 | 8.67 | 0.95 |
| 1296 | 1.0380 | 9.00 | 1.06 |
| 1297 | 1.0465 | 11.20 | 1.19 |
| 1299 | 1.0417 | 10.07 | 1.23 |
| 1300 | 1.0322 | 7.70 | 0.93 |
| 1301 | 1.0312 | 7.36 | 0.91 |
| 1302 | 1.0310 | 7.45 | 0.91 |
| 1303 | 1.0340 | 8.17 | 0.91 |
| 1304 | 1.0292 | 6.88 | 0.88 |
| 1305 | 1.0371 | 9.03 | 1.19 |
| 1306 | 1.0370 | 8.95 | 0.98 |
| 1307(b) | 1.0328 | 7.86 | 1.01 |
| 1481 | 1.0449 | 10.82 | ... |
| 1482 | 1.0444 | 10.83 | ... |
| 1483 | 1.0464 | 11.21 | ... |
| 1484 | 1.0423 | 10.27 | ... |
| 1485 | 1.0347 | 8.55 | ... |
| 1477(c) | 1.0610 | 13.86 | ... |
| 1479 | 1.0411 | 10.00 | 1.21 |
| 1486 | 1.0169 | 4.34 | 0.62 |
| 1491 | 1.0198 | 4.97 | 0.63 |
| 1496 | 1.0341 | 8.27 | 1.15 |
| 1515 | 1.0352 | 8.56 | 1.15 |
| 1529 | 1.0209 | 5.11 | 0.89 |
| 1530 | 1.0252 | 6.21 | 0.98 |
| 1531 | 1.0291 | 7.17 | 1.08 |
| 1224(c) | 1.0486 | 11.22 | 0.91 |
| 1325 | 1.0327 | 7.86 | 0.93 |
Table 2.—Composition of Whole Tomato Pulps Contd.
| Sample No. | Filtrate from pulps | ||||
| Sp. gr. at 20° C. | Solids(a) | Sugar(d) | Acid as citric | Immersion refractometer 17.5° C. | |
| _Per cent_ | _Per cent_ | _Per cent_ | |||
| 1290 | 1.0233 | 5.24 | 2.41 | 0.58 | 36.24 |
| 1291 | 1.0252 | 5.71 | 3.10 | 0.53 | 37.80 |
| 1292 | 1.0211 | 4.88 | 2.48 | 0.49 | 34.51 |
| 1293 | 1.0276 | 6.28 | 3.35 | 0.61 | 40.04 |
| 1294 | 1.0256 | 5.82 | 3.20 | 0.55 | 38.27 |
| 1295 | 1.0340 | 7.69 | 4.36 | 0.67 | 46.03 |
| 1296 | ... | 8.05 | 4.47 | 0.66 | 46.86 |
| 1297 | 1.0446 | 10.27 | 5.61 | 0.89 | 56.70 |
| 1299 | 1.0394 | 9.09 | 4.96 | 0.81 | 51.75 |
| 1300 | 1.0304 | 6.88 | 3.55 | 0.67 | 42.84 |
| 1301 | ... | 6.68 | 3.27 | 0.69 | 41.56 |
| 1302 | 1.0293 | 6.61 | 3.43 | 0.64 | 41.76 |
| 1303 | 1.0323 | 7.29 | 3.77 | 0.71 | 44.65 |
| 1304 | 1.0274 | 6.20 | 3.03 | 0.64 | 39.74 |
| 1305 | ... | 7.98 | 4.14 | 0.82 | 47.30 |
| 1306 | ... | 8.01 | 4.71 | 0.69 | 47.60 |
| 1307(b) | 1.0308 | 6.97 | 3.79 | 0.66 | 43.15 |
| 1481 | 1.0421 | 9.64 | 5.15 | 0.99 | 54.20 |
| 1482 | 1.0422 | 9.86 | 5.62 | 0.94 | 54.75 |
| 1483 | 1.0441 | 10.19 | 5.67 | 0.98 | 56.45 |
| 1484 | 1.0396 | 9.23 | 5.42 | 0.81 | 52.10 |
| 1485 | 1.0332 | 7.73 | 4.35 | 0.72 | 45.85 |
| 1477(c) | 1.0579 | 12.75 | 6.55 | 0.97 | 67.15 |
| 1479 | 1.0386 | 8.96 | ... | ... | 51.57 |
| 1486 | 1.0158 | 3.76 | ... | ... | ... |
| 1491 | 1.0188 | 4.40 | ... | ... | 32.67 |
| 1496 | 1.0318 | 7.31 | ... | ... | 44.86 |
| 1515 | 1.0331 | 7.61 | ... | ... | 46.20 |
| 1529 | 1.0195 | 4.54 | ... | ... | 32.96 |
| 1530 | 1.0231 | 5.42 | ... | ... | 36.31 |
| 1531 | 1.0273 | 6.27 | ... | ... | 40.09 |
| 1224(c) | 1.0468 | 10.33 | ... | ... | 57.62 |
| 1325 | ... | 6.99 | ... | ... | 43.80 |
Table 2.—Composition of Whole Tomato Pulps Contd.
| Sample No. | Ratio of pulp solids to filtrate solids | Insoluble solids in total solids | Solids of filtrate | Refractive constant of filtered liquor(f) | ||
| Sugar(d) | Acid | Ratio sugar to acid | ||||
| _Per cent_ | _Per cent_ | _Per cent_ | ||||
| 1290 | 1.133 | 11.1 | 46.0 | 11.1 | 4.1 | 0.20556 |
| 1291 | 1.145 | 11.9 | 54.3 | 9.4 | 5.8 | 0.20550 |
| 1292 | 1.127 | 14.6 | 50.8 | 10.1 | 5.0 | 0.20564 |
| 1293 | 1.118 | 10.5 | 53.4 | 9.7 | 5.5 | 0.20548 |
| 1294 | 1.113 | 10.6 | 55.0 | 9.5 | 5.8 | 0.20525 |
| 1295 | 1.127 | 11.0 | 56.8 | 8.7 | 6.5 | 0.20534 |
| 1296 | 1.117 | 11.8 | 55.5 | 8.2 | 6.8 | ... |
| 1297 | 1.091 | 10.6 | 54.6 | 8.9 | 6.3 | 0.20544 |
| 1299 | 1.108 | 12.2 | 54.6 | 8.9 | 6.1 | 0.20550 |
| 1300 | 1.119 | 12.1 | 51.6 | 9.7 | 5.3 | 0.20546 |
| 1301 | 1.102 | 12.4 | 48.9 | 10.3 | 4.8 | ... |
| 1302 | 1.127 | 12.2 | 51.9 | 9.7 | 5.4 | 0.20551 |
| 1303 | 1.120 | 11.1 | 51.7 | 9.7 | 5.3 | 0.20549 |
| 1304 | 1.110 | 12.8 | 48.9 | 10.4 | 4.7 | 0.20546 |
| 1305 | 1.132 | 13.2 | 51.9 | 10.3 | 5.0 | ... |
| 1306 | 1.117 | 11.0 | 58.8 | 8.7 | 6.8 | ... |
| 1307(b) | 1.126 | 12.9 | 54.4 | 9.5 | 5.7 | 0.20544 |
| 1481 | 1.123 | ... | 53.4 | 10.3 | 5.2 | 0.20545 |
| 1482 | 1.100 | ... | 57.0 | 9.6 | 6.0 | 0.20554 |
| 1483 | 1.100 | ... | 55.6 | 9.6 | 5.8 | 0.20550 |
| 1484 | 1.114 | ... | 58.7 | 8.8 | 6.7 | 0.20544 |
| 1485 | 1.106 | ... | 56.3 | 9.3 | 6.0 | 0.20529 |
| 1477(c) | 1.111(e) | ... | 51.4 | 7.7 | 6.7 | ... |
| 1479 | 1.116 | 9.8 | ... | ... | ... | 0.20554 |
| 1486 | 1.154 | 14.3 | ... | ... | ... | ... |
| 1491 | 1.128 | 12.7 | ... | ... | ... | 0.20565 |
| 1496 | 1.131 | 13.9 | ... | ... | ... | 0.20554 |
| 1515 | 1.125 | 13.5 | ... | ... | ... | 0.20556 |
| 1529 | 1.125 | 17.4 | ... | ... | ... | 0.20556 |
| 1530 | 1.145 | 15.8 | ... | ... | ... | 0.20553 |
| 1531 | 1.143 | 15.1 | ... | ... | ... | 0.20547 |
| 1224(c) | 1.124(e) | 11.8 | ... | ... | ... | ... |
| 1325 | 1.123 | ... | ... | ... | ... | ... |
(a) Determined by drying in vacuo at 70°C.
(b) Composite of 1290 to 1306, inclusive.
(c) This sample contained salt.
(d) Expressed as invert.
(e) Salt-free ratio.
(f) Calculated by formula of Lorentz-Lorenz, (n2 - 1)/(n2 + 2)2.
Note.—All specific gravities in this bulletin are on a 20°C/20°C basis.
Table 3.—Composition of Trimming Stock Pulps
| Sample No. | Composition of pulps | ||
| Specific gravity at 20° C. | Total solids(a) | Insoluble solids | |
| _Per cent_ | _Per cent_ | ||
| 1470 | 1.0373 | 9.54 | ... |
| 1471 | 1.0385 | 9.40 | ... |
| 1470-1 | 1.0349 | 8.56 | ... |
| 1470-2 | 1.0316 | 7.88 | ... |
| 1470-3 | 1.0284 | 7.00 | ... |
| 1470-4 | 1.0258 | 6.62 | ... |
| 1471-1 | 1.0334 | 8.12 | ... |
| 1471-2 | 1.0258 | 6.41 | ... |
| 1471-3 | 1.0229 | 7.48 | ... |
| 1471-4 | 1.0191 | 4.74 | ... |
| 1572 | 1.0424 | 10.28 | ... |
| 1573 | 1.0392 | 9.53 | 1.22 |
| 1574 | 1.0427 | 10.29 | 1.17 |
| 1575 | 1.0386 | 9.73 | 1.29 |
| 1662(b) | 1.0204 | 4.85 | 0.18 |
| 1664(c) | 1.0577 | 13.20 | 0.62 |
| 1665 | 1.0331 | 7.74 | 1.10 |
| 701 | 1.0200 | 4.89 | 0.72 |
| 703(d) | 1.0180 | 4.24 | 0.10 |
| 705 | 1.0388 | 9.85 | 1.83 |
| 706 | 1.0333 | 8.35 | 0.98 |
Table 3.—Composition of Trimming Stock Pulps Contd.
| Sample No. | Composition of liquor obtained by filtering pulps | ||||
| Specific gravity at 20° C. | Solids(a) | Sugar(e) | Acid as citric | Immersion refractometer at 17.5° C. | |
| _Per cent_ | _Per cent_ | _Per cent_ | |||
| 1470 | 1.0337 | 7.68 | 4.11 | 0.58 | 45.90 |
| 1471 | 1.0334 | 7.62 | 4.05 | 0.59 | 45.75 |
| 1470-1 | 1.0302 | 7.11 | ... | ... | 42.87 |
| 1470-2 | 1.0279 | 6.55 | ... | ... | 40.75 |
| 1470-3 | ... | 5.83 | ... | ... | 37.80 |
| 1470-4 | 1.0232 | 5.53 | ... | ... | 36.40 |
| 1471-1 | 1.0288 | 6.86 | ... | ... | 41.60 |
| 1471-2 | 1.0227 | 5.41 | ... | ... | 36.10 |
| 1471-3 | 1.0275 | 6.14 | ... | ... | 39.25 |
| 1471-4 | 1.0168 | 3.94 | ... | ... | 30.35 |
| 1572 | 1.0400 | 9.28 | ... | ... | 52.47 |
| 1573 | 1.0369 | 8.53 | ... | ... | 49.33 |
| 1574 | 1.0401 | 9.29 | ... | ... | 52.40 |
| 1575 | 1.0369 | 8.28 | ... | ... | 49.37 |
| 1662(b) | 1.0201 | 4.65 | ... | ... | 33.27 |
| 1664(c) | 1.0566 | 12.70 | ... | ... | 66.92 |
| 1665 | 1.0304 | 6.89 | ... | ... | 42.65 |
| 701 | 1.0184 | 4.29 | 2.35 | 0.30 | 32.09 |
| 703(d) | 1.0178 | 4.15 | 2.32 | 0.29 | 32.09 |
| 705 | 1.0359 | 8.08 | 4.07 | 0.51 | 47.85 |
| 706 | ... | 7.29 | 3.51 | 0.46 | 44.69 |
Table 3.—Composition of Trimming Stock Pulps Contd.
| Sample No. | Ratio of pulp solids to filtrate solids | Insoluble solids in total solids | Sugar in solids of liquor | Acid in solids of liquor | Ratio of acid to sugar |
| _Per cent_ | _Per cent_ | _Per cent_ | |||
| 1470 | 1.241 | ... | 53.5 | 7.6 | 7.0 |
| 1471 | 1.233 | ... | 53.2 | 7.7 | 6.9 |
| 1470-1 | 1.203 | ... | ... | ... | ... |
| 1470-2 | 1.203 | ... | ... | ... | ... |
| 1470-3 | 1.201 | ... | ... | ... | ... |
| 1470-4 | 1.197 | ... | ... | ... | ... |
| 1471-1 | 1.184 | ... | ... | ... | ... |
| 1471-2 | 1.184 | ... | ... | ... | ... |
| 1471-3 | 1.218 | ... | ... | ... | ... |
| 1471-4 | 1.203 | ... | ... | ... | ... |
| 1572 | 1.109 | ... | ... | ... | ... |
| 1573 | 1.117 | 12.8 | ... | ... | ... |
| 1574 | 1.109 | 11.4 | ... | ... | ... |
| 1575 | 1.175 | 13.3 | ... | ... | ... |
| 1662(b) | 1.042 | 3.7 | ... | ... | ... |
| 1664(c) | 1.040 | 4.7 | ... | ... | ... |
| 1665 | 1.123 | 14.3 | ... | ... | ... |
| 701 | 1.140 | 14.7 | 54.8 | 7.0 | 7.8 |
| 703(d) | 1.022 | 2.4 | 55.9 | 7.0 | 8.0 |
| 705 | 1.220 | 18.6 | 50.4 | 6.2 | 8.0 |
| 706 | 1.145 | 11.7 | 48.3 | 6.3 | 7.6 |
(a) Determined by drying in vacuo at 70° C.
(b) Unconcentrated tomato juice from peeling table.
(c) No. 1662 concentrated.
(d) Clear liquor separated from unconcentrated pulp on standing.
(e) Expressed as invert.
Table 4.—Comparison of Methods for the Determination and Calculation of
Solids in Whole Tomato Pulp
| Sample No. | Solids in liquor from filtered pulp | |||
| By drying _in vacuo_ at 70° C. | Calculated from-- | |||
| Immersion refractometer reading | Specific gravity(1) | Specific gravity(2) | ||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |
| 1290 | 5.24 | 5.31 | 5.35 | 5.35 |
| 1291 | 5.71 | 5.67 | 5.78 | 5.80 |
| 1292 | 4.88 | 4.87 | 4.85 | 4.85 |
| 1293 | 6.28 | 6.21 | 6.33 | 6.35 |
| 1294 | 5.82 | 5.79 | 5.87 | 5.89 |
| 1295 | 7.69 | 7.67 | 7.82 | 7.82 |
| 1296 | 8.05 | 7.88 | ... | ... |
| 1297 | 10.27 | 10.27 | 10.25 | 10.26 |
| 1299 | 9.09 | 9.06 | 9.05 | 9.06 |
| 1300 | 6.88 | 6.91 | 6.98 | 6.99 |
| 1301 | 6.68 | 6.59 | ... | ... |
| 1302 | 6.61 | 6.64 | 6.73 | 6.74 |
| 1303 | 7.29 | 7.34 | 7.42 | 7.43 |
| 1304 | 6.20 | 6.16 | 6.30 | 6.30 |
| 1305 | 7.98 | 7.98 | ... | ... |
| 1306 | 8.01 | 8.05 | ... | ... |
| 1307 | 6.97 | 6.96 | 7.08 | 7.08 |
| 1481 | 9.64 | 9.67 | 9.68 | 9.68 |
| 1482 | 9.86 | 9.81 | 9.70 | 9.71 |
| 1483 | 10.19 | 10.21 | 10.15 | 10.14 |
| 1484 | 9.23 | 9.15 | 9.10 | 9.11 |
| 1485 | 7.73 | 7.64 | 7.63 | 7.64 |
| 1479 | 8.96 | 9.03 | 8.87 | 8.88 |
| 1486 | 3.76 | ... | 3.62 | 3.63 |
| 1491 | 4.40 | 4.44 | 4.30 | 4.32 |
| 1496 | 7.31 | 7.39 | 7.30 | 7.31 |
| 1515 | 7.61 | 7.70 | 7.60 | 7.61 |
| 1529 | 4.54 | 4.52 | 4.47 | 4.49 |
| 1530 | 5.42 | 5.32 | 5.30 | 5.31 |
| 1531 | 6.27 | 6.25 | 6.27 | 6.28 |
| 1325 | 6.99 | 7.13 | ... | ... |
Table 4.—Comparison of Methods for the Determination and Calculation of
Solids in Whole Tomato Pulp Contd.
| Sample No. | Solids in whole pulp | ||||
| By drying _in vacuo_ at 70° C. | Calculated from immersion refractometer reading | Calculated from specific gravity of-- | |||
| Filtered liquor[3] | Whole pulp | Filtered liquor[4) | |||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |
| 1290 | 5.94 | 5.95 | 6.00 | 5.97 | 5.99 |
| 1291 | 6.54 | 6.36 | 6.48 | 6.47 | 6.50 |
| 1292 | 5.50 | 5.47 | 5.44 | 5.52 | 5.43 |
| 1293 | 7.02 | 6.96 | 7.10 | 6.98 | 7.11 |
| 1294 | 6.48 | 6.49 | 6.58 | 6.45 | 6.60 |
| 1295 | 8.67 | 8.59 | 8.77 | 8.63 | 8.76 |
| 1296 | 9.00 | 8.83 | ... | 9.11 | ... |
| 1297 | 11.20 | 11.50 | 11.47 | 11.20 | 11.49 |
| 1299 | 10.07 | 10.15 | 10.14 | 10.02 | 10.15 |
| 1300 | 7.70 | 7.75 | 7.82 | 7.68 | 7.83 |
| 1301 | 7.36 | 7.38 | ... | 7.43 | ... |
| 1302 | 7.45 | 7.44 | 7.54 | 7.40 | 7.55 |
| 1303 | 8.17 | 8.23 | 8.33 | 8.12 | 8.32 |
| 1304 | 6.88 | 6.90 | 7.06 | 6.95 | 7.06 |
| 1305 | 9.03 | 8.94 | ... | 8.88 | ... |
| 1306 | 8.95 | 9.02 | ... | 8.86 | ... |
| 1307 | 7.86 | 7.81 | 7.93 | 7.83 | 7.93 |
| 1481 | 10.82 | 10.83 | 10.84 | 10.80 | 10.84 |
| 1482 | 10.83 | 10.98 | 10.86 | 10.70 | 10.88 |
| 1483 | 11.21 | 11.43 | 11.36 | 11.17 | 11.36 |
| 1484 | 10.27 | 10.25 | 10.19 | 10.17 | 10.20 |
| 1485 | 8.55 | 8.56 | 8.55 | 8.30 | 8.56 |
| 1479 | 10.00 | 10.10 | 9.94 | 9.88 | 9.85 |
| 1486 | 4.34 | ... | 4.05 | 3.90 | 4.07 |
| 1491 | 4.97 | 4.97 | 4.82 | 4.62 | 4.84 |
| 1496 | 8.27 | 8.28 | 8.18 | 8.15 | 8.29 |
| 1515 | 8.56 | 8.63 | 8.52 | 8.40 | 8.52 |
| 1529 | 5.11 | 5.06 | 5.01 | 4.90 | 5.03 |
| 1530 | 6.21 | 5.97 | 5.94 | 5.97 | 5.95 |
| 1531 | 7.17 | 7.01 | 7.04 | 6.92 | 7.03 |
| 1325 | 7.86 | 7.99 | ... | 7.81 | ... |
(1) From formula on page 30.
(2) The solution factor of O’Sullivan (J. Chem. Soc., 1876, p. 129) was employed with slight
modification. The formula employed was 1000(d - 1000) / 4.35 = per cent solids. In this formula
d = specific gravity of solution at 20° C.
(3) From formula on page 31.
(4) For these figures the formula of footnote 2 was employed and the results multiplied by 1.12
Table 5.—Tomato Pulp and Filtered Liquor
| Whole pulp | Filtrate from pulp | |||||
| Solids by drying | Specific gravity at 20° C. | Solids by drying | Immersion refract- ometer reading at17.5° C. | Specific gravity at 20° C. | ||
| _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | |||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |||
| 3.42 | 3.15 | 1.0150 | 3.05 | 2.71 | 26.9 | 1.0133 |
| 3.47 | 3.20 | 1.0152 | 3.10 | 2.75 | 27.1 | 1.0136 |
| 3.53 | 3.25 | 1.0155 | 3.15 | 2.80 | 27.3 | 1.0138 |
| 3.58 | 3.30 | 1.0157 | 3.20 | 2.85 | 27.5 | 1.0140 |
| 3.64 | 3.35 | 1.0159 | 3.25 | 2.89 | 27.7 | 1.0142 |
| 3.70 | 3.41 | 1.0161 | 3.30 | 2.93 | 27.9 | 1.0144 |
| 3.76 | 3.46 | 1.0163 | 3.35 | 2.97 | 28.1 | 1.0146 |
| 3.81 | 3.51 | 1.0166 | 3.40 | 3.02 | 28.3 | 1.0149 |
| 3.87 | 3.56 | 1.0168 | 3.45 | 3.07 | 28.6 | 1.0151 |
| 3.92 | 3.61 | 1.0170 | 3.50 | 3.11 | 28.8 | 1.0153 |
| 3.98 | 3.67 | 1.0172 | 3.55 | 3.15 | 29.0 | 1.0155 |
| 4.03 | 3.72 | 1.0174 | 3.60 | 3.20 | 29.2 | 1.0157 |
| 4.09 | 3.77 | 1.0177 | 3.65 | 3.24 | 29.4 | 1.0160 |
| 4.15 | 3.82 | 1.0179 | 3.70 | 3.28 | 29.6 | 1.0162 |
| 4.20 | 3.87 | 1.0181 | 3.75 | 3.33 | 29.8 | 1.0164 |
| 4.26 | 3.93 | 1.0183 | 3.80 | 3.38 | 30.0 | 1.0166 |
| 4.31 | 3.98 | 1.0185 | 3.85 | 3.42 | 30.3 | 1.0168 |
| 4.37 | 4.03 | 1.0188 | 3.90 | 3.46 | 30.5 | 1.0170 |
| 4.43 | 4.08 | 1.0190 | 3.95 | 3.51 | 30.7 | 1.0173 |
| 4.48 | 4.13 | 1.0192 | 4.00 | 3.55 | 30.9 | 1.0175 |
| 4 54 | 4.18 | 1.0194 | 4.05 | 3.60 | 31.1 | 1.0177 |
| 4.59 | 4.23 | 1.0197 | 4.10 | 3.64 | 31.3 | 1.0179 |
| 4.65 | 4.28 | 1.0199 | 4.15 | 3.69 | 31.5 | 1.0181 |
| 4.71 | 4.33 | 1.0201 | 4.20 | 3.73 | 31.7 | 1.0183 |
| 4.76 | 4.38 | 1.0203 | 4.25 | 3.78 | 31.9 | 1.0185 |
| 4.82 | 4.44 | 1.0205 | 4.30 | 3.82 | 32.1 | 1.0188 |
| 4.87 | 4.49 | 1.0208 | 4.35 | 3.86 | 32.3 | 1.0190 |
| 4.93 | 4.54 | 1.0210 | 4.40 | 3.91 | 32.5 | 1.0192 |
| 4.99 | 4.59 | 1.0212 | 4.45 | 3.95 | 32.7 | 1.0194 |
| 5.04 | 4.64 | 1.0215 | 4.50 | 4.00 | 32.9 | 1.0196 |
Table 5.—Tomato Pulp and Filtered Liquor—Continued
| Whole pulp | Filtrate from pulp | |||||
| Solids by drying | Specific gravity at 20° C. | Solids by drying | Immersion refract- ometer reading at17.5° C. | Specific gravity at 20° C. | ||
| _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | |||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |||
| 5.10 | 4.70 | 1.0217 | 4.55 | 4.04 | 33.1 | 1.0198 |
| 5.16 | 4.75 | 1.0219 | 4.60 | 4.09 | 33.3 | 1.0200 |
| 5.21 | 4.80 | 1.0222 | 4.65 | 4.13 | 33.6 | 1.0203 |
| 5.27 | 4.85 | 1.0224 | 4.70 | 4.18 | 33.8 | 1.0205 |
| 5.33 | 4.90 | 1.0226 | 4.75 | 4.22 | 34.0 | 1.0207 |
| 5.38 | 4.96 | 1.0228 | 4.80 | 4.26 | 34.2 | 1.0209 |
| 5.44 | 5.01 | 1.0230 | 4.85 | 4.31 | 34.4 | 1.0211 |
| 5.49 | 5.06 | 1.0233 | 4.90 | 4.36 | 34.6 | 1.0213 |
| 5.55 | 5.11 | 1.0235 | 4.95 | 4.40 | 34.8 | 1.0216 |
| 5.60 | 5.16 | 1.0237 | 5.00 | 4.44 | 35.0 | 1.0218 |
| 5.66 | 5.21 | 1.0240 | 5.05 | 4.49 | 35.2 | 1.0220 |
| 5.72 | 5.26 | 1.0242 | 5.10 | 4.53 | 35.4 | 1.0223 |
| 5.77 | 5.31 | 1.0244 | 5.15 | 4.58 | 35.6 | 1.0225 |
| 5.83 | 5.36 | 1.0247 | 5.20 | 4.62 | 35.8 | 1.0227 |
| 5.88 | 5.41 | 1.0249 | 5.25 | 4.66 | 36.0 | 1.0229 |
| 5.94 | 5.47 | 1.0251 | 5.30 | 4.71 | 36.2 | 1.0231 |
| 6.00 | 5.52 | 1.0253 | 5.35 | 4.75 | 36.4 | 1.1333 |
| 6.05 | 5.57 | 1.0256 | 5.40 | 4.80 | 36.6 | 1.0235 |
| 6.11 | 5.62 | 1.0258 | 5.45 | 4.84 | 36.8 | 1.0238 |
| 6.16 | 5.67 | 1.0260 | 5.50 | 4.89 | 37.1 | 1.0240 |
| 6.22 | 5.73 | 1.0263 | 5.55 | 4.93 | 37.3 | 1.0242 |
| 6.28 | 5.78 | 1.0265 | 5.60 | 4.98 | 37.5 | 1.0244 |
| 6.33 | 5.83 | 1.0267 | 5.65 | 5.02 | 37.7 | 1.0246 |
| 6.39 | 5.88 | 1.0270 | 5.70 | 5.06 | 37.9 | 1.0249 |
| 6.45 | 5.93 | 1.0272 | 5.75 | 5.11 | 38.1 | 1.0251 |
| 6.50 | 5.99 | 1.0274 | 5.80 | 5.15 | 38.3 | 1.0253 |
| 6.56 | 6.04 | 1.0276 | 5.85 | 5.20 | 38.5 | 1.0255 |
| 6.61 | 6.09 | 1.0279 | 5.90 | 5.24 | 38.7 | 1.0257 |
| 6.67 | 6.14 | 1.0281 | 5.95 | 5.29 | 38.9 | 1.0259 |
| 6.72 | 6.19 | 1.0283 | 6.00 | 5.33 | 39.1 | 1.0261 |
Table 5.—Tomato Pulp and Filtered Liquor—Continued
| Whole pulp | Filtrate from pulp | |||||
| Solids by drying | Specific gravity at 20° C. | Solids by drying | Immersion refract- ometer reading at17.5° C. | Specific gravity at 20° C. | ||
| _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | |||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |||
| 6.78 | 6.24 | 1.0285 | 6.05 | 5.38 | 39.3 | 1.0263 |
| 6.84 | 6.29 | 1.0288 | 6.10 | 5.42 | 39.5 | 1.0266 |
| 6.89 | 6.35 | 1.0290 | 6.15 | 5.46 | 39.7 | 1.0268 |
| 6.95 | 6.41 | 1.0292 | 6.20 | 5.51 | 39.9 | 1.0270 |
| 7.01 | 6.46 | 1.0294 | 6.25 | 5.56 | 40.1 | 1.0272 |
| 7.06 | 6.51 | 1.0297 | 6.30 | 5.60 | 40.3 | 1.0274 |
| 7.12 | 6.56 | 1.0299 | 6.35 | 5.64 | 40.6 | 1.0277 |
| 7.17 | 6.61 | 1.0301 | 6.40 | 5.69 | 40.8 | 1.0279 |
| 7.23 | 6.66 | 1.0304 | 6.45 | 5.73 | 41.0 | 1.0281 |
| 7.28 | 6.71 | 1.0306 | 6.50 | 5.78 | 41.2 | 1.0283 |
| 7.34 | 6.76 | 1.0308 | 6.55 | 5.82 | 41.4 | 1.0285 |
| 7.40 | 6.82 | 1.0310 | 6.60 | 5.86 | 41.6 | 1.0287 |
| 7.45 | 6.87 | 1.0313 | 6.65 | 5.91 | 41.8 | 1.0290 |
| 7.51 | 6.92 | 1.0315 | 6.70 | 5.95 | 42.0 | 1.0292 |
| 7.56 | 6.97 | 1.0317 | 6.75 | 6.00 | 42.2 | 1.0294 |
| 7.62 | 7.02 | 1.0320 | 6.80 | 6.04 | 42.4 | 1.0296 |
| 7.68 | 7.08 | 1.0322 | 6.85 | 6.09 | 42.6 | 1.0298 |
| 7.74 | 7.13 | 1.0324 | 6.90 | 6.14 | 42.8 | 1.0300 |
| 7.79 | 7.18 | 1.0326 | 6.95 | 6.18 | 43.1 | 1.0303 |
| 7.85 | 7.23 | 1.0329 | 7.00 | 6.22 | 43.3 | 1.0305 |
| 7.90 | 7.28 | 1.0331 | 7.05 | 6.26 | 43.5 | 1.0307 |
| 7.96 | 7.33 | 1.0333 | 7.10 | 6.31 | 43.7 | 1.0309 |
| 8.02 | 7.38 | 1.0336 | 7.15 | 6.36 | 43.9 | 1.0311 |
| 8.07 | 7.43 | 1.0338 | 7.20 | 6.40 | 44.1 | 1.0313 |
| 8.12 | 7.48 | 1.0340 | 7.25 | 6.44 | 44.3 | 1.0315 |
| 8.18 | 7.54 | 1.0342 | 7.30 | 6.48 | 44.5 | 1.0318 |
| 8.24 | 7.59 | 1.0345 | 7.35 | 6.53 | 44.7 | 1.0320 |
| 8.30 | 7.64 | 1.0347 | 7.40 | 6.58 | 44.9 | 1.0322 |
| 8.35 | 7.69 | 1.0349 | 7.45 | 6.62 | 45.1 | 1.0324 |
| 8.40 | 7.74 | 1.0352 | 7.50 | 6.66 | 45.3 | 1.0326 |
Table 5.—Tomato Pulp and Filtered Liquor—Continued
| Whole pulp | Filtrate from pulp | |||||
| Solids by drying | Specific gravity at 20° C. | Solids by drying | Immersion refract- ometer reading at17.5° C. | Specific gravity at 20° C. | ||
| _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | |||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |||
| 8.46 | 7.79 | 1.0354 | 7.55 | 6.71 | 45.5 | 1.0328 |
| 8.52 | 7.84 | 1.0356 | 7.60 | 6.76 | 45.7 | 1.0331 |
| 8.57 | 7.89 | 1.0358 | 7.65 | 6.80 | 45.9 | 1.0333 |
| 8.63 | 7.95 | 1.0361 | 7.70 | 6.84 | 46.2 | 1.0335 |
| 8.68 | 8.00 | 1.0363 | 7.75 | 6.89 | 46.4 | 1.0337 |
| 8.74 | 8.05 | 1.0365 | 7.80 | 6.93 | 46.6 | 1.0339 |
| 8.80 | 8.11 | 1.0367 | 7.85 | 6.98 | 46.8 | 1.0341 |
| 8.86 | 8.16 | 1.0370 | 7.90 | 7.02 | 47.0 | 1.0344 |
| 8.91 | 8.21 | 1.0372 | 7.95 | 7.07 | 47.2 | 1.0346 |
| 8.96 | 8.26 | 1.0374 | 8.00 | 7.11 | 47.4 | 1.0348 |
| 9.02 | 8.31 | 1.0377 | 8.05 | 7.16 | 47.6 | 1.0350 |
| 9.08 | 8.36 | 1.0379 | 8.10 | 7.20 | 47.8 | 1.0352 |
| 9.14 | 8.41 | 1.0381 | 8.15 | 7.24 | 48.0 | 1.0354 |
| 9.19 | 8.46 | 1.0383 | 8.20 | 7.28 | 48.2 | 1.0357 |
| 9.25 | 8.51 | 1.0386 | 8.25 | 7.33 | 48.4 | 1.0359 |
| 9.30 | 8.57 | 1.0388 | 8.30 | 7.38 | 48.6 | 1.0361 |
| 9.36 | 8.62 | 1.0390 | 8.35 | 7.42 | 48.8 | 1.0363 |
| 9.42 | 8.67 | 1.0393 | 8.40 | 7.46 | 49.0 | 1.0366 |
| 9.47 | 8.72 | 1.0395 | 8.45 | 7.51 | 49.2 | 1.0368 |
| 9.53 | 8.77 | 1.0397 | 8.50 | 7.55 | 49.4 | 1.0370 |
| 9.58 | 8.83 | 1.0400 | 8.55 | 7.60 | 49.6 | 1.0372 |
| 9.64 | 8.88 | 1.0402 | 8.60 | 7.64 | 49.8 | 1.0374 |
| 9.70 | 8.93 | 1.0404 | 8.65 | 7.68 | 50.0 | 1.0376 |
| 9.75 | 8.98 | 1.0406 | 8.70 | 7.73 | 50.2 | 1.0379 |
| 9.80 | 9.03 | 1.0408 | 8.75 | 7.78 | 50.4 | 1.0381 |
| 9.86 | 9.09 | 1.0410 | 8.80 | 7.82 | 50.7 | 1.0383 |
| 9.92 | 9.14 | 1.0413 | 8.85 | 7.86 | 50.9 | 1.0385 |
| 9.97 | 9.19 | 1.0415 | 8.90 | 7.91 | 51.1 | 1.0387 |
| 10.02 | 9.24 | 1.0417 | 8.95 | 7.95 | 51.3 | 1.0389 |
| 10.08 | 9.29 | 1.0419 | 9.00 | 8.00 | 51.5 | 1.0392 |
Table 5.—Tomato Pulp and Filtered Liquor—Continued
| Whole pulp | Filtrate from pulp | |||||
| Solids by drying | Specific gravity at 20° C. | Solids by drying | Immersion refract- ometer reading at17.5° C. | Specific gravity at 20° C. | ||
| _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | |||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |||
| 10.14 | 9.35 | 1.0421 | 9.05 | 8.05 | 51.7 | 1.0394 |
| 10.19 | 9.40 | 1.0424 | 9.10 | 8.09 | 51.9 | 1.0396 |
| 10.25 | 9.45 | 1.0426 | 9.15 | 8.13 | 52.1 | 1.0398 |
| 10.30 | 9.50 | 1.0428 | 9.20 | 8.18 | 52.3 | 1.0400 |
| 10.35 | 9.55 | 1.0430 | 9.25 | 8.22 | 52.5 | 1.0402 |
| 10.41 | 9.60 | 1.0433 | 9.30 | 8.27 | 52.7 | 1.0404 |
| 10.47 | 9.65 | 1.0435 | 9.35 | 8.31 | 52.9 | 1.0406 |
| 10.52 | 9.70 | 1.0437 | 9.40 | 8.35 | 53.1 | 1.0409 |
| 10.58 | 9.75 | 1.0440 | 9.45 | 8.40 | 53.3 | 1.0411 |
| 10.64 | 9.80 | 1.0442 | 9.50 | 8.45 | 53.5 | 1.0413 |
| 10.70 | 9.86 | 1.0444 | 9.55 | 8.49 | 53.7 | 1.0415 |
| 10.75 | 9.91 | 1.0447 | 9.60 | 8.53 | 53.9 | 1.0417 |
| 10.80 | 9.96 | 1.0449 | 9.65 | 8.58 | 54.1 | 1.0419 |
| 10.86 | 10.01 | 1.0451 | 9.70 | 8.62 | 54.3 | 1.0422 |
| 10.91 | 10.06 | 1.0453 | 9.75 | 8.67 | 54.5 | 1.0424 |
| 10.97 | 10.11 | 1.0456 | 9.80 | 8.71 | 54.7 | 1.0426 |
| 11.02 | 10.16 | 1.0458 | 9.85 | 8.75 | 55.0 | 1.0428 |
| 11.08 | 10.21 | 1.0461 | 9.90 | 8.80 | 55.2 | 1.0430 |
| 11.14 | 10.26 | 1.0463 | 9.95 | 8.85 | 55.4 | 1.0433 |
| 11.20 | 10.31 | 1.0465 | 10.00 | 8.89 | 55.6 | 1.0435 |
| 11.25 | 10.37 | 1.0467 | 10.05 | 8.93 | 55.8 | 1.0437 |
| 11.30 | 10.42 | 1.0469 | 10.10 | 8.98 | 56.0 | 1.0439 |
| 11.36 | 10.47 | 1.0472 | 10.15 | 9.02 | 56.2 | 1.0441 |
| 11.41 | 10.52 | 1.0474 | 10.20 | 9.07 | 56.4 | 1.0444 |
| 11.47 | 10.57 | 1.0476 | 10.25 | 9.11 | 56.6 | 1.0446 |
| 11.53 | 10.63 | 1.0478 | 10.30 | 9.15 | 56.8 | 1.0448 |
| 11.59 | 10.68 | 1.0481 | 10.35 | 9.20 | 57.0 | 1.0450 |
| 11.64 | 10.73 | 1.0483 | 10.40 | 9.25 | 57.2 | 1.0452 |
| 11.70 | 10.78 | 1.0485 | 10.45 | 9.29 | 57.4 | 1.0454 |
| 11.75 | 10.83 | 1.0487 | 10.50 | 9.33 | 57.6 | 1.0457 |
Table 5.—Tomato Pulp and Filtered Liquor—Continued
| Whole pulp | Filtrate from pulp | |||||
| Solids by drying | Specific gravity at 20° C. | Solids by drying | Immersion refract- ometer reading at17.5° C. | Specific gravity at 20° C. | ||
| _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | |||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |||
| 11.81 | 10.89 | 1.0490 | 10.55 | 9.38 | 57.8 | 1.0459 |
| 11.87 | 10.94 | 1.0492 | 10.60 | 9.42 | 58.0 | 1.0461 |
| 11.93 | 10.99 | 1.0494 | 10.65 | 9.47 | 58.2 | 1.0463 |
| 11.99 | 11.04 | 1.0496 | 10.70 | 9.51 | 58.4 | 1.0465 |
| 12.05 | 11.09 | 1.0499 | 10.75 | 9.55 | 58.6 | 1.0467 |
| 12.10 | 11.15 | 1.0501 | 10.80 | 9.60 | 58.8 | 1.0469 |
| 12.15 | 11.20 | 1.0503 | 10.85 | 9.65 | 59.0 | 1.0471 |
| 12.21 | 11.25 | 1.0505 | 10.90 | 9.70 | 59.2 | 1.047 |
| 12.26 | 11.30 | 1.0508 | 10.95 | 9.74 | 59.4 | 1.0476 |
| 12.32 | 11.35 | 1.0510 | 11.00 | 9.78 | 59.6 | 1.0478 |
| 12.37 | 11.40 | 1.0512 | 11.05 | 9.82 | 59.9 | 1.0480 |
| 12.43 | 11.45 | 1.0515 | 11.10 | 9.87 | 60.1 | 1.0482 |
| 12.49 | 11.50 | 1.0517 | 11.15 | 9.92 | 60.3 | 1.0484 |
| 12.55 | 11.55 | 1.0519 | 11.20 | 9.96 | 60.5 | 1.0487 |
| 12.60 | 11.60 | 1.0522 | 11.25 | 10.00 | 60.7 | 1.0489 |
| 12.65 | 11.66 | 1.0524 | 11.30 | 10.04 | 60.9 | 1.0491 |
| 12.71 | 11.71 | 1.0526 | 11.35 | 10.09 | 61.1 | 1.0493 |
| 12.77 | 11.76 | 1.0528 | 11.40 | 10.13 | 61.3 | 1.0495 |
| 12.83 | 11.81 | 1.0531 | 11.45 | 10.18 | 61.5 | 1.0498 |
| 12.88 | 11.86 | 1.0533 | 11.50 | 10.22 | 61.7 | 1.0500 |
| 12.94 | 11.92 | 1.0535 | 11.55 | 10.27 | 61.9 | 1.0502 |
| 12.99 | 11.97 | 1.0538 | 11.60 | 10.31 | 62.1 | 1.0504 |
| 13.05 | 12.02 | 1.0540 | 11.65 | 10.35 | 62.3 | 1.0506 |
| 13.10 | 12.07 | 1.0542 | 11.70 | 10.40 | 62.5 | 1.0508 |
| 13.16 | 12.12 | 1.0544 | 11.75 | 10.45 | 62.7 | 1.0511 |
| 13.22 | 12.18 | 1.0547 | 11.80 | 10.49 | 62.9 | 1.0513 |
| 13.27 | 12.23 | 1.0549 | 11.85 | 10.53 | 63.1 | 1.0515 |
| 13.32 | 12.28 | 1.0551 | 11.90 | 10.58 | 63.3 | 1.0517 |
| 13.38 | 12.33 | 1.0554 | 11.95 | 10.63 | 63.5 | 1.0519 |
| 13.44 | 12.38 | 1.0556 | 12.00 | 10.67 | 63.7 | 1.0521 |
Table 5.—Tomato Pulp and Filtered Liquor—Continued
| Whole pulp | Filtrate from pulp | |||||
| Solids by drying | Specific gravity at 20° C. | Solids by drying | Immersion refract- ometer reading at17.5° C. | Specific gravity at 20° C. | ||
| _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | _In vacuo_ at 70° C. | At atmospheric pressure 100° C. | |||
| _Per cent_ | _Per cent_ | _Per cent_ | _Per cent_ | |||
| 13.50 | 12.44 | 1.0558 | 12.05 | 10.71 | 64.0 | 1.0523 |
| 13.55 | 12.49 | 1.0560 | 12.10 | 10.75 | 64.2 | 1.0525 |
| 13.60 | 12.54 | 1.0562 | 12.15 | 10.80 | 64.4 | 1.0527 |
| 13.66 | 12.59 | 1.0565 | 12.20 | 10.84 | 64.6 | 1.0529 |
| 13.72 | 12.64 | 1.0567 | 12.25 | 10.89 | 64.8 | 1.0531 |
| 13.78 | 12.70 | 1.0569 | 12.30 | 10.94 | 65.0 | 1.0533 |
| 13.83 | 12.75 | 1.0572 | 12.35 | 10.98 | 65.2 | 1.0535 |
| 13.89 | 12.80 | 1.0574 | 12.40 | 11.02 | 65.4 | 1.0537 |
| 13.95 | 12.85 | 1.0576 | 12.45 | 11.07 | 65.6 | 1.0539 |
| 14.01 | 12.90 | 1.0579 | 12.50 | 11.11 | 65.8 | 1.0541 |
The per cent of solids in the filtered liquor obtained by drying in vacuo, multiplied by 1.12, gives the per cent of solids in the original pulp obtained by drying in vacuo. This relationship is shown in [Table 2], in the column headed “Ratio of pulp solids to filtrate solids,” and also in [Table 5].
Of the 33 samples shown in [Table 2], the result obtained by multiplying the per cent of solids in the filtrate (obtained by drying in vacuo) by the factor 1.12 is very nearly identical with the per cent of solids in the pulp (obtained by drying in vacuo). In 22 of the 33 samples the difference between these two figures is less than 0.1 per cent. In 17 samples it is less than 0.06 per cent, and in 13 samples it is less than 0.05 per cent. In only two samples does it exceed 0.17 per cent.
(b) By calculation from the specific gravity of the filtrate.—The specific gravity of the filtered liquor may be determined by means of an ordinary pycnometer. From the specific gravity at 20° C., the per cent of solids in the filtrate as determined by drying in vacuo at 70° C. may be obtained from [Table 5]. It may also be calculated by the following formula, which was derived from the same table:
Per cent Solids in Filtrate = 230 (sp. gr. of filtrate - 1.000).
The per cent of solids in the pulp may also be ascertained from the specific gravity of the filtrate at 20° C., from [Table 5]. The same results may be obtained from the following formula, which was derived from [Table 4]:
Per cent Solids in Pulp = 257.5 (sp. gr. of filtrate at 20° C. - 1.000).
It is of interest to note that the table suggested by Windisch for the determination of extract in wine (Bureau of Chemistry, U. S. Dept. Agri., Bull. 107, revised, Table V) may be employed to determine solids in tomato pulp from the specific gravity of the filtered liquor from the same. If the specific gravity of the liquor be determined at 20° C., the figures in the adjoining column, under “Extract,” correspond very closely to the per cent of total solids in the original pulp. A still closer agreement is obtained if the figure 0.05 be deducted from the percentage of extract given in the table.
(c) By calculation from the index of refraction of the filtrate.—The index of refraction of the liquor obtained by filtering tomato pulp may be determined by means of either the Zeiss-Abbé refractometer, or the immersion refractometer at the temperature of 17.5° C. The latter is preferable as it permits of much greater accuracy. The corresponding percentage of solids in the filtrate and the percentage of solids in the pulp from which it is prepared may be ascertained from the index of refraction by [Table 5]. The per cent of solids in the filtrate may also be calculated from the scale reading of the immersion refractometer at 17.5° C. by the following formula, which is derived from [Table 5]:
Per cent Solids in Filtrate = 0.258 (scale reading - 15) - 0.0165 (scale reading - 26.4).
If the index of refraction has been determined by means of an Abbé refractometer, the per cent of solids in the filtrate may be calculated by the following formula:
Per cent Solids in Filtrate = 666(nD - 1.3332) - 20.7(nD - 1.3376).
The per cent of total solids in tomato pulp may also be ascertained from the index of refraction of the liquor prepared by filtering the pulp as shown in [Table 5]; or it may be calculated from the immersion refractometer reading by the following formula, which is derived from [Table 5]:
Per cent Solids in Pulp = 0.289(scale reading of filtrate - 15) - 0.0185(scale reading - 26.4).
If the index of refraction of the filtrate has been determined by means of an Abbé refractometer, the per cent of solids in the pulp may be calculated by the following formula:
Per cent Solids in Pulp = 748(nD - 1.3332) - 25.5(nD - 1.3376).
It is of interest to note that the relation between the index of refraction of the liquor obtained by filtering tomato pulp and the per cent of solids in that liquid is very similar to the relation between the index of refraction and dissolved solids in beer and wine extract, as shown in the table prepared by Wagner.[12]
In the formula given above, as well as in [Table 5], it is assumed that salt is absent. If it be desired to calculate the percentage of solids in a sample containing salt from the index of refraction of the filtrate, it is necessary first to determine the amount of salt present and make correction therefor (see p. 34). For this purpose the table of Wagner[13] may be employed. The correction of the immersion refractometer reading amounts to 0.45 for each tenth per cent of salt present.
This correction is necessary if the percentage of solids be determined by drying, or calculated from specific gravity.
Determination of Insoluble Solids
Transfer 20 grams of the pulp to an eight-ounce nursing bottle, nearly filled with hot water, mix by shaking, and centrifuge until the insoluble matter is collected in a cake in the bottom of the bottle. Transfer the supernatant liquor onto a double, tared filter paper covering the bottom of a Büchner funnel, using suction to facilitate filtration.
Again fill the nursing bottle with hot water, stir the cake of insoluble solids so that it is thoroughly mixed with the water, centrifuge, and decant the supernatant liquor on the filter. Repeat the centrifuging and the filtration of the supernatant liquor once more, and then finally transfer the insoluble solids to the filter paper and thoroughly wash with hot water. Dry the paper and insoluble solids, and weigh. The insoluble solids are quite hydroscopic and the weight must be taken quickly.
Determination of Sugar
The sugar of tomatoes is probably always present as invert sugar. If cane sugar is ever present in the raw product it is doubtless inverted during the concentration of pulp. The per cent of sugar given in [Tables 2] and [3] was determined by the method of Munson and Walker.[14]
Determination of Acidity
Accurate results cannot be obtained by the titration of tomato products in the presence of the insoluble solids. If it be desired to determine the acidity in the entire sample of tomatoes or tomato pulp rather than in the expressed juice, the insoluble solids should first be removed by the method given in the determination of insoluble solids or by filtration through filter paper. The per cent of acid given in [Tables 2] and [3] was obtained by titrating the liquor obtained by filtering the pulp. In products of this nature, the addition of an alkali causes a brownish color which has a tendency to obscure the end point shown by the indicator. To obviate this, the sample should be diluted to at least 200 cc. and a larger amount of indicator employed than is necessary with a clear solution. The following details are suggested.
Dilute 20 grams of the filtrate under examination with over 200 cc. of water. Add at ½ cc. of phenolphthalein solution (prepared by dissolving 1 gram of phenolphthalein in 100 cc. of 95 per cent alcohol) and titrate with sodium hydroxide until the end point is obtained. Add 1 cc. of tenth-normal hydrochloric acid, heat the solution quickly to boiling and boil one minute to expel carbon dioxide. Cool the solution quickly to about room temperature, and then add tenth-normal sodium hydroxide until the end point is obtained. The volume of hydrochloric acid added must, of course, be taken into consideration in the final result. The filtrate may also be titrated direct with tenth-normal sodium hydroxide solution with satisfactory results.
Determination of Salt
This laboratory has been using the following rapid method which gives results agreeing closely with results obtained by the analysis of the ash:
Weigh out 20 grams of pulp, dilute in a volumetric flask to 200 cc., filter and titrate an aliquot portion with standard silver nitrate solution, using potassium chromate as indicator. The acidity of tomato pulp is not sufficient to interfere with this determination.
Determination of Specific Gravity[15]
The specific gravity of tomato pulp is used as one criterion for establishing the value of pulp that is offered for sale and is also used in connection with the manufacture of pulp to determine the point at which evaporation should be stopped.
In the former case there is ample time for making the examination, and conditions may be established which permit a reasonable degree of accuracy in the work.
In the determination of the specific gravity of hot pulp during the process of its evaporation speed is essential, and the conditions of a manufacturing plant do not always permit a high degree of accuracy. It becomes necessary, therefore, to consider what methods may give the highest degree of accuracy obtainable under the conditions of the work and at the same time afford quick results.
Tomato pulp, owing to its high viscosity, retains a large quantity of air bubbles which increase the volume of the pulp and hence interfere with the accuracy of the determination of specific gravity. In working with cold pulp this air may be eliminated by whirling in a centrifuge. With hot pulp that operation is impossible, and the specific gravity must be determined in the presence of the air bubbles mentioned. Moreover, in working with cold pulp the temperature can be more accurately controlled, and the error caused by variation in temperature can be corrected. With hot pulp these conditions cannot be obtained nearly so well. The determination of specific gravity of hot pulp is therefore only roughly approximate at best. Where time permits it is strongly advisable to cool the pulp under conditions that prevent evaporation before determining specific gravity.
The importance of accuracy in the determination of specific gravity in tomato pulp is discussed on page 50.
Methods are given below for the determination of specific gravity in both hot and cold pulp.
When salt has been added, the amount should be determined and a correction applied by deducting .007 from the specific gravity for each per cent of salt present.
(a) COLD PULP AFTER CENTRIFUGING TO ELIMINATE AIR BUBBLES
This method may be employed for pulp of any degree of concentration or for unconcentrated cyclone juice. A specific gravity flask such as is shown in Figure 1 is used together with a “2-bottle” Babcock milk tester (the centrifuge referred to below). The flask may be obtained of Eimer & Amend, Third Avenue, 18th to 19th Streets, New York City, or of Emil Greiner & Co., 55 Fulton Street, New York City, and in ordering it should be designated as “specific gravity flask for tomato pulp of Pyrex glass with a capacity of about 125 cc.” The “2-bottle” Babcock milk tester may be obtained of any dairy supply house. It may also be obtained of any dealer in chemical apparatus by designating it as E. & A. No. 1833.
The specific gravity flask may be calibrated as follows:
Obtain the weight of the flask after thoroughly cleaning and drying, fill to overflowing with water (preferably boiled and cooled distilled water) and remove the excess water from the mouth of the flask by means of a straight edge. Wipe dry and weigh immediately. If the flask full of water is weighed at any other temperature than 20° C. (68° F.) a correction must be made to obtain the weight at that temperature. These corrections are as follows:
| Temperature | Correction to be added with flasks having a volume of— | ||
| Fahrenheit | Centigrade | 125 cc. | 400 cc. |
| Grams | Grams | ||
| 69 | 20.6 | .02 | .05 |
| 70 | 21.1 | .03 | .09 |
| 71 | 21.7 | .05 | .14 |
| 72 | 22.2 | .06 | .20 |
| 73 | 22.8 | .08 | .25 |
| 74 | 23.3 | .09 | .30 |
| 75 | 23.9 | .11 | .35 |
| 76 | 24.4 | .13 | .41 |
| 77 | 25.0 | .15 | .47 |
| 78 | 25.6 | .17 | .53 |
| 79 | 26.1 | .18 | .59 |
| 80 | 26.7 | .20 | .65 |
| 81 | 27.2 | .22 | .71 |
| 82 | 27.8 | .24 | .77 |
| 83 | 28.3 | .26 | .83 |
| 84 | 28.9 | .28 | .89 |
| 85 | 29.4 | .30 | .96 |
| 86 | 30.0 | .32 | 1.02 |
If it is desired to use somewhat larger samples and thus secure correspondingly more accurate results, a similar flask, but made somewhat larger (capacity approximately 400 cc.), may be employed. Such a flask, with a diameter of a little over 3 inches, is illustrated in Figure 2. This larger flask will not fit into the Babcock tester, and when it is used a special head for the Babcock tester must be made. Such a head is illustrated in Figure 3, and can be made by any good tinner.
The larger flask shown in Figure 2 holds a heavier weight than the Babcock machine is intended to carry, and the advisability of its use is perhaps questionable. In any case, whatever size flask is used, it is important to build a guard around the centrifuge in order to protect the operator when the apparatus gives way, as it eventually will.
Fig. 1. Small Specific Gravity Flask.
Fig. 2. Large Specific Gravity Flask.
Dimensions given are outside measurements. Thickness of walls is about 3/64 in.
Fig. 3. Special Head and Flask Receptacles for Babcock Milk Tester.
The details of the method of determining specific gravity by the use of this apparatus are as follows:
Fill the flask shown in Figure 1 with the sample of pulp and place in the centrifuge (the Babcock milk tester mentioned above). Place a suitable counterpoise[16] in the other receptacle of the centrifuge. Whirl for from one-half to one minute at a speed of about 1,000 revolutions per minute, that is with the handle turning about 100 revolutions per minute. Because of the air bubbles removed by whirling, the surface of the pulp will now be considerably below the top of the flask. Fill the flask and whirl in the centrifuge again. Repeat this filling and whirling until the flask is practically full of pulp after whirling. Ordinarily two or three separate whirlings are sufficient. Then add a few more drops of pulp so that the pulp comes above the top of the flask, and strike off flush with the top of the flask with a straight edge. Wash the outside of the flask, wipe dry, and weigh. Then read the specific gravity of the pulp from a table prepared, giving the weight of the flask full of pulp and the specific gravity of the pulp in parallel columns, or calculate the specific gravity as described below.
While the weight is being taken a thermometer may be placed in the pulp remaining in the can or dipper from which the flask was filled. If the temperature varies from 68° F. the specific gravity may be corrected by [Table 8]. In order to use this method the temperature of the pulp should not be below 50° F., or above 86° F.; otherwise, it should be warmed or cooled, as described above.
The method is accurate, simple, easily operated and fairly rapid. To calculate the specific gravity from the weights obtained, the weight of the clean, dry flask and of the water it contains at 68° F. are necessary. The weight of the clean, dry flask is then subtracted from the weight of the flask full of pulp to obtain the net weight of the pulp. This divided by the weight of the water the flask will contain at 68° F., gives the specific gravity.
A table can be constructed readily for each flask, which will give in parallel columns the weight of the flask full of pulp and the corresponding specific gravity. This greatly simplifies the determination, as it eliminates all calculation. When such a table is employed a balance giving actual weights is practically as convenient as one reading specific gravity directly. It has the very important advantage that the balance, weights, and flask may be tested from time to time.
In preparing such a table it is convenient first to draw a curve representing specific gravities of the pulp and corresponding weights of the flask full of pulp of various degrees of specific gravity. The table may then be constructed from the curve.
For instance, let us suppose that the flask weighs 56.00 grams and that when full of water at 68° F. (20° C.) it weighs 176.63 grams. The water contained at the temperature mentioned then weighs (176.63 - 56.00) 120.63 grams. Now the specific gravity of the pulp is its weight compared with the weight of an equal volume of water. Having the figures given above we can easily calculate the weight of the flask filled with pulp of any desired specific gravity. We may therefore calculate the weight of the flask plus pulp of two different specific gravities; mark those points on a sheet of coordinate paper with specific gravity of the pulp entered at the bottom and the weight of flask plus pulp at the side, and a straight line drawn through the two points mentioned gives us the weight of the flask when filled with pulp of any specific gravity.
For instance, if the flask mentioned above be filled with a pulp of the specific gravity of 1.03, the weight of the pulp is (120.63 × 1.03) 124.25 grams. This added to the weight of the flask (56.00 grams) gives us 180.25 grams. Similarly, if the flask be filled with pulp of 1.04 specific gravity the weight of the contents at 68° F. will be (120.63 × 1.04) 125.46 grams. This added to the weight of the flask (56.00 grams) gives 181.46 grams as the weight of flask plus pulp. Now if a sheet of coordinate paper be prepared with specific gravities entered at the bottom and weight of flask plus pulp at the side, these points may be entered. This is done in Figure 4 and the two points mentioned are each indicated by a circle and are connected by a straight line. A table may be constructed from this line, giving the weights of flask plus pulp in one column and the corresponding specific gravity in another.
Fig. 4. Weight and Specific Gravity of Tomato Pulp.
As an illustration of this there are given below a series of figures illustrating the beginning of the table that could be constructed from Figure 4. If a large sheet of coordinate paper be taken the line shown in Figure 4 may be extended so that a table may be constructed for pulp of all concentrations.
| Weight of
flask and pulp | Specific gravity |
| 180.25 | 1.0300 |
| 180.31 | 1.0305 |
| 180.37 | 1.0310 |
| 180.43 | 1.0315 |
| 180.49 | 1.0320 |
| 180.55 | 1.0325 |
| 180.61 | 1.0330 |
| 180.67 | 1.0335 |
The highest degree of accuracy can be secured by filling the flask and making the weighing at exactly 68° F. This is obviously not practicable under factory conditions, however, and satisfactory results can be secured by taking the temperature of the pulp at the time of weighing and correcting for temperature by the use of [Table 8]. This table gives the correction to be added to the specific gravity when the pulp is taken at temperatures between 68° and 86° F., and the correction to be deducted from the specific gravity for temperatures, between 55° and 68° F. As a matter of principle, correction factors should be avoided as far as practicable, and the smaller the correction factor the more accurate the results will be. This table will be found especially useful in determining the specific gravity of the partly concentrated pulp, as is directed on page 50.
As stated above, in determining specific gravity by this method it is advisable that the reading be made to the second place of decimals. For this purpose an assay pulp balance is suggested. An assay pulp balance carrying a maximum load of 300 grams is listed by dealers in chemical apparatus at $52.50. This balance may be obtained from dealers in chemical apparatus by designating it as “Assay pulp balance E. & A. No. 292, capacity 300 grams.” The same balance, more heavily built, and preferable for that reason, carrying a maximum capacity of 600 grams, is listed at $63.
A satisfactory set of weights, suitable for weighing a cup similar to that shown in Figure 1, may be obtained from any dealer in chemical apparatus by designating it as E. & A. No. 516, “Metric brass weights in wooden box, 200 grams to 1 centigram.” This is listed at $5.50.
For convenience, all of the apparatus necessary for using this method of determining specific gravity is listed below. With the exception of the specific gravity flask this apparatus may be purchased of any dealer in chemical supplies. The specific gravity flasks have not heretofore been available except through this laboratory, which purchased a considerable quantity of them and supplied them to manufacturers of pulp as long as this supply lasted. At the urgent request of the writer, Eimer & Amend and Emil Greiner & Co., both of New York City, have finally stocked this item and stand ready to supply it to those wishing to secure it.
- Specific gravity flask for tomato pulp, of Pyrex glass, 1½ × 6¼ inches (outside measurements), capacity about 125 cc.
- Two-bottle Babcock milk tester, with 2 brass holders, E. & A. No. 1883.
- Assay pulp balance, maximum load 300 grams, E. & A. No. 292.
- Metric brass weights in wooden box, 200 grams to 1 centigram, E. & A. No. 516.
- Chemical thermometer, 50 to 212° F. [17]
(b) COLD PULP WITHOUT CENTRIFUGING
A method frequently employed for determining the specific gravity of cold pulp is to fill the cup by pouring, strike off with a straight edge, wash the outside, dry and weigh. As ordinarily practiced, this determination is attended by considerable error. If the balance is arranged for reading specific gravity directly, weights should be at hand for determining the accuracy of the balance and the weight of the flask, and both should be checked from time to time. The pulp on being poured into the flask or cup carries with it air bubbles to such an extent as to materially reduce the weight. Attempts to remove these air bubbles without the use of a centrifuge have not been successful. This is shown in [Table 7], in the column headed “Pouring cold and whirling by hand.” The figures given in this column were obtained by weighing the sample after it had been whirled vigorously in the cup shown in Fig. 5 until air bubbles appeared to be eliminated. From 50 to 175 revolutions were given the cup in each of the determinations whose results are shown in this column. Even then it will be noted by comparison with Column 1 that the results are low. As the method is ordinarily practiced in the plant, without any attempt to remove the air bubbles by whirling, the results obtained are likely to be less accurate than those shown in the column just mentioned.
(c) SPECIFIC GRAVITY OF HOT PULP
Many manufacturers of tomato pulp control the concentration of their product by determining specific gravity when the evaporation is almost completed. They therefore desire the results at the earliest possible moment, and there is no attempt to cool the sample before determining specific gravity, although in that way much more accurate results could be obtained.
When necessary to use this method the hot pulp is poured into the specific gravity flask (Fig. 1 or Fig. 2) by means of a dipper until the flask overflows. The top is then “struck off” with a straight edge and the flask placed in a shallow basin of water and the pulp carefully washed from the outside. The temperature of the pulp remaining in the dipper is then determined by means of a chemical thermometer.
The flask is then dried with a towel, which operation is greatly facilitated by the heat of the pulp. The cooling of the contents of the flask causes contraction, so that after washing the flask is not entirely full. This should be disregarded, as it is desired to determine the weight of the amount of pulp that filled the flask originally. As soon as the outside of the flask is clean and dry the flask and contents are weighed.
The apparent specific gravity of the hot pulp is ascertained from the special table prepared for the flask according to the directions given on page 38, and the correction figure for the temperature of the pulp obtained from [Table 6] is added. For example, this method when applied to a certain sample of hot pulp (without centrifuging) indicated a specific gravity of 0.9874. The temperature of the pulp was found to be 201° F. In [Table 6] we find that the correction .0457 is equivalent to 201° F. Adding this to the apparent specific gravity given above, we have 0.9874 × 0.457 or 1.033 which is as nearly as we can determine from the hot pulp the specific gravity that would have been determined by examining the same sample after cooling by method (a). More accurate results can be obtained by working with larger specific gravity flasks. For instance, the specific gravity cup shown in Figure 5 may be made of copper, and may readily be made larger than the glass flasks shown in Figures 1 and 2. All metal flasks will gradually change in weight, owing to the solution of metal by the hot tomato pulp, and their weight should therefore be checked from time to time.
Table 6.—Corrections for Specific Gravity of Hot Pulp
| Temp. °F. | Correction |
| 190 | .0401 |
| 191 | .0406 |
| 192 | .0411 |
| 193 | .0416 |
| 194 | .0421 |
| 195 | .0426 |
| 196 | .0431 |
| 197 | .0436 |
| 198 | .0441 |
| 199 | .0447 |
| 200 | .0452 |
| 201 | .0457 |
| 202 | .0462 |
| 203 | .0466 |
| 204 | .0472 |
| 205 | .0477 |
| 206 | .0482 |
| 207 | .0487 |
| 208 | .0492 |
| 209 | .0498 |
| 210 | .0504 |
| 211 | .0510 |
| 212 | .0515 |
With a materially larger cup or flask (which should be of metal) a heavier balance and heavier weights should be used than suggested on page 40. In using a specific gravity cup similar to that shown in Figure 5 but holding about 1,000 grams of pulp an assay pulp balance with a capacity of 1,500 can be employed, or owing to the increased accuracy of the larger sample a less accurate and cheaper scale such as the “Howard trip scale,” or better a box scale such as is listed as E. & A. 338, may be employed. In working with a cup of this size a set of weights ranging from 1000 grams to 1 centigram is necessary.
The determination of specific gravity in hot pulp is attended by considerable error. Even if the flask or cup be carried directly to the kettle, and filled as quickly as possible, the pulp is materially cooled in transferring, and by the time the surface is “struck off” sufficient contraction may occur to increase the weight of the contents of the flask and cause material error.
When a pail of hot pulp is carried to another room or building for the determination of specific gravity, the error caused by cooling may be increased. Again, notwithstanding the fact that the pulp is hot, enough air bubbles become incorporated into it in pouring into the cup to make a considerable difference in the weight. These two errors counter balance each other to some extent, but it is impossible to control the manipulation with sufficient uniformity to secure satisfactory results.
Fig. 5. Specific Gravity Cup for Hot Pulp.
The figures obtained in the second column of [Table 7] (under the heading “Pouring at boiling temperature”) show the error of this method with carefully calibrated apparatus and working under the best conditions. By comparison with the first column, it will be noted that the results are always low, and that the difference between individual determinations is so great that a correction factor cannot be established. It should be borne in mind that these results were obtained by chemists. When the method is employed even by careful operators in the plant, still greater discrepancies may be expected.
Table 7.—Comparison of Different Methods of Determining Specific Gravity [18]
| Sample Number | Specific gravity by different methods of filling cup or flask. | |||
| Centrifuging at 68°F. | Pouring cold and whirling by hand | Pouring at boiling temperature | Dipping at boiling temperature | |
| 1477 | 1.0610 | ... | 1.0464 | ... |
| Do | 1.0610 | ... | 1.0449 | ... |
| Do | ... | ... | 1.0600 | ... |
| 1484 | 1.0423 | 1.0330 | 1.0380 | ... |
| 1485 | 1.0347 | ... | 1.0336 | ... |
| 1483 | 1.0464 | 1.0437 | 1.042 | ... |
| Do | ... | 1.0420 | 1.0446 | ... |
| Do | ... | 1.0430 | ... | ... |
| Do | ... | 1.0442 | ... | ... |
| 1482 | 1.0441 | 1.0416 | 1.0360 | ... |
| Do | 1.0444 | 1.0419 | 1.0410 | ... |
| Do | 1.0447 | 1.0424 | 1.0413 | ... |
| 1481 | 1.0449 | 1.0410 | 1.040 | ... |
| Do | 1.0449 | 1.0410 | 1.041 | ... |
| Do | ... | 1.0418 | 1.0397 | ... |
| 1480 | ... | 1.0430 | 1.036 | ... |
| Do | ... | 1.0420 | 1.040 | ... |
| Do | ... | 1.0429 | 1.044 | ... |
| Do | ... | ... | 1.0407 | ... |
| 1496 | 1.0340 | 1.0330 | ... | ... |
| Do | 1.0341 | 1.0326 | ... | ... |
| Do | ... | 1.0326 | ... | ... |
| Do | ... | 1.0346 | ... | 1.0299 |
| Do | ... | 1.0341 | ... | 1.0303 |
| Do | ... | 1.0341 | ... | 1.0343 |
| Do | ... | ... | ... | 1.033 |
| 1515 | 1.0351 | ... | ... | 1.036 |
| Do | 1.0352 | ... | ... | 1.035 |
| 1519 | 1.0380 | ... | ... | 1.0377 |
| Do | ... | ... | ... | 1.0383 |
| Do | ... | ... | ... | 1.0329 |
| Do | ... | ... | ... | 1.0350 |
| 1521 | 1.0440 | ... | 1.0410 | 1.0439 |
| Do | ... | ... | 1.0439 | 1.0448 |
| 1522 | 1.0500 | ... | 1.0428 | 1.0493 |
| Do | ... | ... | 1.0455 | 1.0508 |
| 1524 | 1.0519 | ... | ... | 1.0504 [46] |
| 1524 | ... | ... | ... | 1.0529 |
| Do | ... | ... | ... | 1.0510 |
| 1526 | 1.0519 | ... | 1.0472 | 1.0529 |
| Do | ... | ... | 1.0463 | 1.0525 |
| 1528 | 1.0519 | ... | 1.0509 | 1.0514 |
| Do | ... | ... | 1.0485 | 1.0514 |
| 1530 | 1.0252 | ... | 1.0281 | 1.0260 |
| Do | ... | ... | ... | 1.0264 |
| Do | ... | ... | ... | 1.0269 |
| 1531 | 1.0291 | ... | 1.0312 | 1.0294 |
| Do | ... | ... | ... | 1.0311 |
| Do | ... | ... | ... | 1.0313 |
It was thought that better results might be secured by modifying the construction of a cup in such a manner as to permit it to be filled by dipping below the surface of the pulp in the kettle. A bail made of 3/16-inch wire was, therefore, soldered to the opposite side of the cup (see Fig. 5). By means of the bail the cup was lowered into the kettle. After it was filled with the pulp the attempt was made to remove air bubbles by repeatedly giving the bail a quick twist or circular motion with a sudden stop. The cup was then brought quickly to the surface of the kettle and “struck off” with a straight edge, the outside of the cup and bail washed quickly with water, dried, and the cup and contents weighed.
In using this method the steam is turned off, and as soon as the foam subsides the cup is sunk well below the surface of the pulp. At this time the heat in various portions of the kettle is of course uniform, by reason of the thorough mixture caused by the vigorous boiling. Owing to the large mass of rather viscous material, and the heat of the kettle itself, the contents of the kettle cool slowly, and even after 10 minutes the temperature does not decrease more than 1° F., except at the very surface of the pulp. As a result of several observations, it was found that a thermometer bulb held 3 inches below the surface of the pulp showed a lowering of temperature of not more than 1° F. in 10 minutes and a lowering of only 0.5° F. in from 5 to 7 minutes.
The bail employed was about 6½ inches wide and 8 inches long. There was some difficulty, owing to the pulp spattering on the hands of the operator because of the air escaping from the cup. This might be diminished by the use of a longer bail, or by wearing suitable gloves. When evaporating tanks are used it will probably be necessary to attach the bail to a stick or support of some kind. In addition to permitting this method of filling, the bail has the additional advantage that the cup full of pulp may be handled for washing and conveying to the balance much more conveniently and with less danger of spilling than with the handle on the side of the cup. Again, the bail does not heat when the cup is filled with hot pulp, and for that reason is easier to handle.
(d) HYDROMETER METHOD
Hydrometers are of little value in determining the specific gravity of tomato pulp. With cold pulp they cannot be used at all. With hot pulp a relatively slender hydrometer comes to rest and readings can be taken with more or less accuracy. The value of the reading is relative to the specific gravity of the pulp and varies with the shape of the hydrometer and with the character of the pulp. It is necessary therefore to obtain the relation between the reading of the hydrometer in the hot pulp and the specific gravity (obtained by an accurate method) of the same pulp cooled without evaporation. In the hands of a careful operator some manufacturers have found hydrometers (used with hot pulp) helpful in making pulp of uniform specific gravity.
The hydrometer gives much more accurate results with the filtrate of pulp. As shown on page 31, there is a direct relation between the specific gravity of tomato pulp and of the liquor obtained by filtering or straining the same, so that when the specific gravity of the latter is known that of the former may be ascertained readily by means of a table. This method is peculiarly applicable to the examination of cyclone juice and light pulp from which the insoluble solids may be removed quickly by straining through a cloth, and it therefore affords the most rapid method that is available to the average factory for determining the specific gravity of cyclone juice.
In [Table 8] are given a series of corrections making it possible to use this method at any temperature between 50 and 80° Fahrenheit. The more closely the readings are taken to 68° F. the more accurate the results. Moreover, when it is attempted to strain the insoluble solids from hot pulp or cyclone juice, considerable evaporation occurs, causing concentration of the product and producing an error in the results. When hot pulp is handled, therefore, it must be strained as quickly as possible, and more accurate results may be obtained if the pulp is cooled quickly before straining. This may be done by placing in a large can and stirring vigorously while the can stands in ice water, or shaking under water in a large flask.
There are several forms of hydrometer which may be used for determining the specific gravity of the filtrate. The ordinary specific gravity hydrometer is the most logical form to use, since it gives the specific gravity directly. Unfortunately, specific gravity hydrometers with the particular marking required for this work are not a stock article, and would, therefore, have to be made to order. For this reason they would be difficult to obtain and not easily replaced if broken.
The Brix hydrometer appears to solve the difficulty. This hydrometer has no direct relation to specific gravity, but Brix readings can, of course, be converted to the specific gravity readings by a table arranged in parallel columns. [Table 9] gives the specific gravity of tomato pulp and the corresponding Brix reading of the filtrate. The Brix hydrometer gives directly the per cent of sugar in a solution of cane sugar, one degree Brix being equivalent to one per cent sugar at the temperature for which the hydrometer was calibrated. This fact and the ordinary purpose for which the instrument is manufactured are of no interest to us in this connection, however. The Brix hydrometer of the range desired for the examination of cyclone juice and pulp is a stock article and can be secured readily.
The instrument can be used with the same accuracy as the specific gravity hydrometer, and the results obtained by it, after correcting for temperature by [Table 8], are converted into terms of specific gravity by means of [Table 9]. The determination of the specific gravity of pulp by means of the hydrometer reading of the filtrate obtained from the pulp has several advantages over the ordinary method of weighing a measured quantity of the pulp. When applied to pulp manufactured from whole tomatoes, the method is reasonably accurate. It is also very rapid and the equipment required is inexpensive. This method is especially applicable to the examination of pulp manufactured from whole tomatoes. It is less applicable to trimming stock pulp, although even with that product the method will be of value, especially for the examination of cyclone juice for the purpose of controlling concentration. With pulp manufactured from trimming stock, the relation of the specific gravity of the pulp to the specific gravity of the filtrate obtained from it will vary according to the nature of the raw material used and also according to the method of manufacture. It seems probable, therefore, that after a manufacturer has determined this relation as applied to his own product, he may be able to use this method with reasonable accuracy even in connection with trimming stock pulp.
The method is adapted especially to the examination of cold pulp or cyclone juice.
- 1 Brix hydrometer, graduated at 20.0° C., with a range of 1–10°, graduated in 1/10°.
- 1 Cylinder of heavy glass, lipped, height 12 inches, diameter 2 inches.
- 1 Chemical thermometer, graduated in Fahrenheit system up to 212° F.
Since this apparatus is likely to be broken, it is well for each plant that contemplates using the method to equip itself with at least two of each item mentioned above.
The Brix hydrometer mentioned above is suggested because it is a stock article handled by all dealers in chemical apparatus and can be secured quickly. It has the disadvantage that it is relatively large, and in order to use it the filtrate must be prepared in much larger quantity than would be required by a smaller hydrometer. By placing orders well in advance with dealers in chemical apparatus special hydrometers may be made with a bulb about one-half inch in diameter and with a total length of five or six inches. Such hydrometers could be used with a cylinder as small as one inch in diameter. They would require much less liquor than is necessary for the Brix hydrometer and therefore would enable the analyst to obtain results much more quickly. In securing such hydrometers it would be well to order several at a time, since it would require several weeks to replace any that may be broken.
The details of the method are as follows:
Place a piece of cotton cloth of about the texture of ordinary glass toweling over a clean, dry container 10 or 12 inches in diameter or over a No. 10 can. Pour on the cloth a suitable amount of the pulp or cyclone juice to be examined, pick the cloth up by the corners and squeeze gently to separate the greater part of the insoluble solids. The strained liquid left in the vessel will be more or less turbid, according to the pressure exerted in squeezing. The amount of insoluble material producing this turbidity, however, is not usually sufficient to interfere with the examination of the product by means of a hydrometer. If, however, it is necessary to exert considerable pressure to get the amount of filtrate desired and the turbidity is therefore considerable it will be necessary to pass the liquor through a second filter, which, of course, may be done quickly.
Transfer this strained liquid, which for the sake of convenience we will designate as “filtrate,” to the 2-inch cylinder described above, and lower the Brix hydrometer into it until the hydrometer floats. When the hydrometer, becomes stationary, the reading on the stem is taken. In reading the hydrometer it will be noted that, owing to the meniscus, the liquid immediately at the stem rises one or two divisions above the general surface. The reading at the lowest point of the surface is desired. In reading the stem, therefore, allowance for the meniscus should be made and a reading recorded one or two divisions on the scale below the extreme height of the meniscus on the stem. The reading so obtained is recorded as the Brix hydrometer reading of the filtrate.
After determining the Brix reading of the filtrate from the tomato pulp, the corresponding specific gravity of the pulp may be obtained from [Table 9]. The result obtained by the method should be corrected to the temperature of 68° F., according to [Table 8]. If it is desired to use the reading of the filtrate from cyclone juice for the purpose of controlling the evaporation of tomato pulp, suitable directions are given below under “Evaporation to Specific Gravity Desired.”