AUTHORITIES CITED IN PART THIRD.
[170] Vines; Physiology of Plants. Nägeli; Beiträge zur näheren Kenntniss der Stärkegruppe.
[171] Bulletin 5, Department of Agriculture, Division of Chemistry, pp. 191 et seq.: Bulletin 25, New Hampshire Experiment Station.
[172] Spencer; Handbook for Sugar Manufacturers, p. 31.
[173] Vid. op. cit. supra, pp. 102, 108.
[174] Journal of the American Chemical Society, Vol. 16, p. 677.
[175] Botanical Gazette, Vol. 12, No. 3.
[176] Bulletin de l’Association des Chimistes de Sucrerie et de Distillerie, Tome 13, p. 133.
[177] Journal of Analytical and Applied Chemistry, Vol. 4, p. 381.
[178] Spencer’s Handbook for Sugar Manufacturers, pp. 30 et seq.
[179] Bulletin de l’Association des Chimistes de Sucrerie et de Distillerie, Tome 13, p. 292.
[180] Vid. op. cit. supra, Tome 2, p. 369.
[181] Dosage du Sucre Cristallisable dans la Betterave, pp. 117 et seq.: Journal of the American Chemical Society, Vol. 16, p. 266.
[182] Neue Zeitschrift für Rübenzucker-Industrie. Band 3, S. 342; Band 14, S. 286: Zeitschrift des Vereins für die Rübenzucker-Industrie, 1876, S. 692: Dingler’s Polytechnisches Journal, Band 232, S. 461.
[183] Sidersky: Traité d’ Analyse des Matières Sucrées, p. 304.
[184] Neue Zeitschrift für Rübenzucker-Industrie, Band 14, S. 286.
[185] Zeitschrift des Vereins für die Rübenzucker-Industrie, Band 32, S. 861.
[186] Spencer’s Handbook for Sugar Manufacturers, p. 42.
[187] Bulletin No. 4 of the Chemical Society of Washington, pp. 22, et seq.
[188] Vid. op. et loc. cit. 7.
[189] Chemiker-Zeitung, Band 19, S. 1830.
[190] Vid. op cit. supra, S. 1784.
[191] Vid. op. cit. supra, S. 1829.
[192] Zeitschrift des Vereins für die Rübenzucker-Industrie, 1895, S. 844.
[193] Journal des Fabricants de Sucre, 1895, No. 33.
[194] Journal of the American Chemical Society, Vol. 2, p. 387: Agricultural Science, Feb. 1892.
[195] American Chemical Journal, Vol. 13, p. 24.
[196] Tucker; Manual of Sugar Analysis, p. 287: Wiechmann; Sugar Analysis, p. 51.
[197] Sidersky; vid. op. cit., 14, p. 197.
[198] Journal of the American Chemical Society, Vol. 18, p. 81: Allen; Commercial Organic Analysis, Vol. 1, p. 291.
[199] Handbuch der Physiologisch- und Pathologisch-Chemischen Analyse, S. 286.
[200] Kühne und Chittenden; American Chemical Journal, Vol. 6, p. 45.
[201] Vid. op. cit. supra, p. 289.
[202] Analyst, Vol. 13, p. 64.
[203] Journal American Chemical Society, Vol. 18, p. 438.
[204] School of Mines Quarterly, Vols. 11 and 12.
In a later method (School of Mines Quarterly, Vol. 13, No. 3) Wiechman describes the separation of the sugars by one polariscopic and two gravimetric determinations, one before and one after inversion. The polariscopic examination is made in a ten per cent solution at a temperature of 20°. The gyrodynats of sucrose, dextrose and levulose at the temperature mentioned are fixed at 66.5, 53.5 and -81.9 respectively. The gravimetric determinations are conducted according to the methods already described. In the formulas for calculating the results a represents sucrose, b reducing sugars, x the dextrose, y the levulose, and d the observed polarization expressed in degrees angular measure. The gyrodynats of sucrose, dextrose and levulose divided by 100 are represented by s, d and l. The calculations are made from the following formulas:
(as + xd) - yl = p.
(as + xd) = p + yl.
xd = p + yl - as.
| x = | p + yl - as |
| d |
In this calculation the gyrodynat of levulose is about ten degrees lower than that of most authorities.
[205] Vid. op. cit., 23, Band 24, S. 869.
[206] Vid. op. cit. supra, 1888, S. 782.
[207] Neue Zeitschrift für Rübenzucker-Industrie, Band 35, S. 166.
[208] Journal of the American Chemical Society, Vol. 2, p. 399: Science, Oct. 1, 1881: Proceedings American Association for the Advancement of Science, 1881, p. 61: Sugar Cane, Vol. 13, p. 533, pp. 61-66.
[209] Wiley and McElroy; Agricultural Science, Vol. 6, p. 57.
[210] Chemical News, Vol. 46, p. 175.
[211] Vid. op. cit, 14, p. 352.
[212] Vid. op. et loc. cit., 41.
[213] Vid. op. cit., 41, Vol. 65, p. 169.
[214] Zeitschrift des Vereins für die Rübenzucker-Industrie, 1884, S. 854.
[215] Bulletin 46, Division of Chemistry, U. S. Department of Agriculture, p. 60.
[216] The Analyst, Vol. 20, p. 121.
[217] Journal American Chemical Society, Vol. 15, p. 668.
[218] Comptes rendus, Tome 118, p. 147.
[219] Journal of the Chemical Society, Transactions, 1895, p. 735.
[220] Die agrikultur-chemische Versuchsstation, Halle, a/S., S. 114.
[221] Cellulose, p. 77.
[222] Vid. op. cit., 46, p. 63.
[223] Zeitschrift für physiologische Chemie, Band 13, S. 84.
[224] Zeitschrift für angewandte Chemie, 1895, S. 561.
[225] Vid. op. cit., 52, pp. 8 et seq.
[226] Vid. op. cit. supra, p. 15.
[227] Composition of Wood, Agricultural Science, Vol. 7, pp. 49, 97 and 161.
[228] Tollens; Handbuch der Kohlenhydrate: von Lippmann; Chemie der Zuckerarten.
PART FOURTH.
FATS AND OILS.
277. Nomenclature.—The terms fat and oil are often used interchangeably and it is difficult in all cases to limit definitely their application. The consistence of the substance at usual room temperatures may be regarded as a point of demarcation. The term fat, in this sense, is applied to glycerids which are solid or semi solid, and oil to those which are quite or approximately liquid. A further classification is found in the origin of the glycerids, and this gives rise to the groups known as animal or vegetable fats and oils. In this manual, in harmony with the practices mentioned above, the term fat will be used to designate an animal or vegetable glycerid which is solid, and the term oil one which is liquid at common room temperature, viz., about 20°. There are few animal oils, and few vegetable fats when judged by this standard, and it therefore happens that the term oil is almost synonymous with vegetable glycerid and fat with a glycerid of animal origin. Nearly related to the fats and oils is the group of bodies known as resins and waxes. This group of bodies, however, can be distinguished from the fats and oils by chemical characteristics. The waxes are ethers formed by the union of fatty acids and alcohols of the ethane, and perhaps also of the ethylene series.[229] This chemical difference is not easily expressed and the terms themselves often add confusion to the meaning, as for instance, japan wax is composed mostly of fats, and sperm oil is essentially a wax.
278. Composition.—Fats and oils are composed chiefly of salts produced by the combination of the complex base glycerol with the fat acids. Certain glycerids, as the lecithins, contain also phosphorus in organic combinations, nitrogen, and possibly other inorganic constituents in organic forms. By the action of alkalies the glycerids are easily decomposed, the acid combining with the inorganic base and the glycerol becoming free. The salts thus produced form the soaps of commerce and the freed base, when collected and purified, is the glycerol of the trade.
When waxes are decomposed by alkalies, fatty acids and alcohols of the ethane series are produced.
The natural glycerids formed from glycerol, which is a trihydric (triatomic) alcohol, are found in the neutral state composed of three molecules of the acid, united with one of the base. If R represent the radicle of the fat acid the general formula for the chemical process by which the salt is produced is:
| Glycerol. | Acid. | Salt. | Water. | ||
| O.H | O.R | ||||
| C₃H₅ | O.H | + 3R.OH = | C₃H₅ | O.R | + 3H₂O. |
| O.H | O.R | ||||
The resulting salts are called triglycerids or neutral glycyl ethers.[230] In natural animal and vegetable products, only the neutral salts are found, the mono- and diglycerids resulting from artificial synthesis. For this reason the prefix tri is not necessarily used in designating the natural glycerids, stearin, for instance, meaning the same as tristearin.
279. Principal Glycerids.—The most important glycerids which the analyst will find are the following:
| Olein, | C₃H₅O(O.C₁₈H₃₃O)₃. |
| Stearin, | C₃H₅O(O.C₁₈H₃₅)₃. |
| Palmitin, | C₃H₅O(O.C₁₆H₃₁O)₃. |
| Linolein, | C₃H₅O(O.C₁₈H₃₁O)₃. |
| Butyrin, | C₃H₅O(O.C₄H₇O)₃. |
Olein is the chief constituent of most oils; palmitin is found in palm oil and many other natural glycerids; stearin is a leading constituent of the fats of beeves and sheep, and butyrin is a characteristic constituent of butter, which owes its flavor largely to this glycerid and its nearly related concomitants.
280. Extraction of Oils and Fats.—Preparatory to a physical and chemical study of the fats and oils is their separation from the other organic matters with which they may be associated. In the case of animal tissues this is usually accomplished by the application of heat. The operation known as rendering may be conducted in many different ways. For laboratory purposes, the animal tissues holding the fat are placed in a convenient dish and a degree of heat applied which will liquify all the fat particles and free them from their investing membranes. The temperature employed should be as low as possible to secure the desired effect, but fats can be subjected for some time to a heat of a little more than 100°, without danger of decomposition. The direct heat of a lamp, however, should not be applied, since it is difficult to avoid too high a temperature at the point of contact of the flame and dish. The dry heat of an air-bath or rendering in an autoclave or by steam is preferable. The residual animal matter is subjected to pressure and the combined liquid fat freed from foreign matters by filtering through a jacket filter, which is kept at a temperature above the solidifying point of the contents.
On a large scale, as in rendering lard, the fat is separated by steam in closed vats which are strong enough to withstand the steam pressure employed. For analytical purposes it is best to extract the fat from animal tissues in the manner described, since the action of solvents is slow on fat particles enveloped in their containing membranes, and the fats, when extracted, are liable to be contaminated with extraneous matters. In dried and ground flesh meal, however, the fat may be extracted with the usual solvents. For the quantitive determination of fat in bones or flesh, the sample, as finely divided as possible, is thoroughly dried, and the fat separated from an aliquot finely powdered portion by extraction with chloroform, ether, or petroleum. The action of anhydrous ether on dried and powdered animal matters is apparently a continuous one. Dormeyer has shown that even after an extraction of several months additional matter goes into solution.[231] The fat in such cases can be determined by saponification with alcoholic potash and the estimation of the free fatty acids produced.
From vegetable substances, such as seeds, the fat is extracted either by pressure or by the use of solvents. For quantitive purposes, only solvents are employed. The dry, finely ground material is exhausted with anhydrous ether or petroleum spirit, in one of the convenient forms of apparatus already described ([33->43]). In very oily seeds great difficulty is experienced in securing a fine state of subdivision suited to complete extraction. In such cases it is advisable to conduct the process in two stages. In the first stage the material, in coarse powder, is exhausted as far as possible and the percentage of oil determined. The residue is then easily reduced to a fine powder, in an aliquot part of which the remaining oil is determined in the usual way.
Fig. 79.—Oil Press.
In securing oils for physical and chemical examination both pressure and solution may be employed. The purest oils are secured by pressure at a low temperature. To obtain anything like a good extraction some sort of hydraulic pressure must be used. In this laboratory a press is employed in which the first pressure is secured by a screw and this is supplemented by hydraulic pressure in which glycerol is the transmitting liquid. The construction of the press is shown in the accompanying [figure].
The whole press is warmed to nearly 100°. The hot finely ground oily material, enclosed in a cloth bag, is placed in the perforated cylinder and compressed as firmly as possible by turning with the hands the wheel shown at the top of the [figure]. The final pressure is secured by the screw shown at the bottom of the figure whereby a piston is driven into a cylinder containing glycerol. The degree of pressure obtained is equal to 300 atmospheres.
Even with the best laboratory hydraulic pressure not more than two-thirds of the total oil contents of oleaginous seeds can be secured and the process is totally inapplicable to securing the oil from tissues when it exists in quantities of less than ten per cent. To get practically all of the oil the best method is to extract with carefully distilled petroleum of low boiling point.
In the preparation of this reagent the petroleum ether of commerce, containing bodies boiling at temperatures of from 35° to 80°, is repeatedly fractioned by distillation until a product is obtained which boils at from 45° to 60°. The distillation of this material is conducted in a large flask heated with steam, furnished with a column containing a number of separatory funnels and connected with an appropriate condenser. The distillate is secured in a bottle packed with broken ice, as shown in [Fig. 80]. A thermometer suspended in the vapor of the petroleum serves to regulate the process. Too much care to avoid accidents cannot be exercised in this operation. Not only must steam be used in heating, but all flame and fire must be rigidly excluded from the room in which the distillation takes place, and the doors leading to other rooms where gas jets may be burning must be kept closed. In the beginning of the process, as much as possible of the petroleum boiling under 45° must be removed and rejected. The distillation is then continued until the temperature rises above 60°. The parts of the distillate saved between these temperatures are redistilled under similar conditions. Other portions of the petroleum, boiling at other temperatures, may be secured in the same way. The products may be in a measure freed of unpleasant odors by redistilling them from a mixture with lard. When used for quantitive purposes the petroleum ether must leave no residue when evaporated at 100°.
Fig. 80.—Apparatus for Fractional Distillation
of Petroleum Ether.
281. Freeing Extracted Oils from Petroleum.—The petroleum ether which is used for extracting oils tends to give them an unpleasant odor and flavor and its entire separation is a matter of some difficulty. The greater part of the solvent may be recovered as described in paragraph [43]. Heating the extracted oil for several hours in thin layers, will remove the last traces of the solvent, but affords opportunity for oxidation, especially in the case of drying oils. An effective means of driving off the last traces of petroleum is to cause a current of dry carbon dioxid to pass through the sample contained in a cylinder and heated to a temperature of from 85° to 90°. The atmosphere of the inert gas will preserve the oil from oxidation and the sample will, as a rule, be found free of the petroleum odor after about ten hours treatment. Ethyl ether or chloroform may be used instead of petroleum, but these solvents act on other matters than the glycerids, and the extract is therefore liable to be contaminated with more impurities than when the petroleum ether is employed. Other solvents for fats are carbon tetrachlorid, carbon disulfid, and benzene. In general, petroleum ether should be employed in preference to other solvents, except in the case of castor oil, which is difficultly soluble in both petroleum and petroleum ethers.
282. Freeing Fats Of Moisture.—Any excess of water in glycerids will accumulate at the bottom of the liquid sample and can be removed by decanting the fat or separating it from the oil by any other convenient method. The warm oil may be almost entirely freed of any residual moisture by passing it through a dry filter paper in a jacket funnel kept at a high temperature. A section showing the construction of such a funnel with a folded filter paper in place, is shown in [Fig. 81]. The final drying, when great exactness is required, is accomplished in a vacuum, or in an atmosphere of inert gas, or in the cold in an exsiccator over sulfuric acid. In drying, it is well to expose the hot oil as little as possible to the action of the air. Wherever convenient, it should be protected from oxidation by some inert gas or a vacuum.
283. Sampling for Analysis.—It is a matter of some difficulty to secure a representative sample of a fat or oil for analytical purposes. The moisture in a fat is apt to be unevenly distributed, and the sampling is to be accomplished in a manner to secure the greatest possible uniformity. When the quantity of material is of considerable quantity a trier may be used which will remove a cylindrical or partly cylindrical mass from the whole length or depth. By securing several subsamples of this kind, and well mixing them, an average sample of the whole mass may be secured. Where the fat is found in different casks or packages samples should be drawn from each as described above. The subsamples are mixed together in weights corresponding to the different casks from which they are taken and the mass obtained by this mixture divided into three equal portions. Two of these parts are melted in a dish at a temperature not exceeding 60°, with constant stirring, and when fully liquid the third part is added. As a rule, the liquid fat retains enough heat to melt the added quantity. As soon as the mixed fats begin to grow pasty the mass is vigorously stirred to secure an intimate mixture of the water and other foreign bodies.[232]
Fig. 81.—Section Showing Construction of a Funnel
for Hot Filtration.
In the case of butter fat the official chemists recommend that subsamples be drawn from all parts of the package until about 500 grams are secured. The portions thus drawn are to be perfectly melted in a closed vessel at as low a temperature as possible, and when melted the whole is to be shaken violently for some minutes till the mass is homogeneous, and sufficiently solidified to prevent the separation of the water and fat. A portion is then poured into the vessel from which it is to be weighed for analysis, and this should nearly or quite fill it. This sample should be kept in a cold place till analyzed.[233]
284. Estimation of Water.—In the official method for butter fat, which may be applied to all kinds, about two grams are dried to constant weight, at the temperature of boiling water, in a dish with flat bottom, having a surface of at least twenty square centimeters.
The use of clean dry sand or asbestos is admissible, and is necessary if a dish with round bottom be employed.
In the method recommended by Benedikt, about five grams of the sampled fat are placed in a small flask or beaker and dried at 100° with occasional stirring to bring the water to the surface.
According to the method of Sonnenschein, the sample is placed in a flask carrying a cork, with an arrangement of glass tubes, whereby a current of dry air may be aspirated over the fat during the process of drying. When the flask is properly fitted its weight is taken, the fat put in and reweighed to get the exact amount. The fat is better preserved by aspirating carbon dioxid instead of air.[234] The moisture may also be readily determined by drying on pumice stone, as described in paragraph [26]. In this case it is well to conduct the desiccation in vacuum or in an inert atmosphere to prevent oxidation.