214. Examination of the Bagasse.—The method just described for the examination of canes may be also applied to the analysis of bagasses, with the changes made necessary by the increased percentage of fiber therein. On account of the large surface exposed by the bagasse, the sampling, shredding and weighing should be accomplished as speedily as possible to avoid loss of moisture.
The optical examination of bagasses is rendered difficult by reason of the uneven pressure to which the canes are subjected. With fairly good milling in technical work the bagasses will have at least thirty per cent of fiber. The method for the polariscopic examination is therefore based upon that assumption, but the volume of the solution must be changed for varying percentages of fiber in the bagasse. On account of the smaller percentage of sugar, it is convenient to take double or three times the normal weight of the bagasse for examination. Since large sugar flasks are not commonly to be had the diffusion of the bagasse may be conducted in a quarter liter flask. In a quarter liter flask place 52.096 grams of the finely shredded bagasse, very nearly fill the flask with water and extract the sugar as described for canes in the foregoing paragraphs. In the weight of bagasse used there will be, in round numbers, fifteen grams of fiber. When the volume of water is completed to the mark the actual content of liquid in the flask will therefore be only 235 cubic centimeters. Fifty cubic centimeters of the filtrate are placed in a sugar flask marked at fifty and fifty-five cubic centimeters, the proper quantity of lead subacetate solution added, the volume completed to the upper mark, the contents of the flask well shaken, filtered and polarized in a 200 millimeter tube. Let the reading obtained be four degrees and increase this by one-tenth for the increased volume of solution above fifty cubic centimeters. The true reading is therefore four degrees and four-tenths. This reading, however, must be corrected, because the original volume instead of being 200 cubic centimeters, is 235 cubic centimeters. The actual percentage of sugar in the sample examined is obtained by the following proportion:
200 : 235 = 4.4 : x.
The correct reading is therefore 5°.2, the percentage of sugar in the sample examined.
The results obtained by the method just described may vary somewhat from the true percentage by reason of the variation of the content of fiber in the bagasse. It is, however, sufficiently accurate for technical control in sugar factories and on account of its rapidity of execution is to be preferred for this purpose. More accurate results would be obtained by drying the bagasse, and proceeding with the examination in a manner entirely analogous to that described for the extraction of sugar from dried canes by aqueous alcohol. In both instances the reducing sugar is determined in the manner already mentioned.
215. Determination of Fiber in Cane.—In estimating the content of sugar in canes by the analysis of the expressed juices, it is important to make frequent determinations of the fiber for the purpose of obtaining correct data for calculation. In periods of excessive drought, or when the canes are quite mature, the relative content of fiber is increased, while, on the other hand, in case of immature canes, or during excessive rainfalls, it is diminished. The chief difficulty in determining the content of fiber in canes is found in securing a representative sample. On account of the hard and fibrous nature of the envelope and of their nodular tissues, canes are reduced to a fine pulp with great difficulty by the apparatus in ordinary use. A fairly homogeneous pulp, however, may be obtained by means of the shredder described on [page 9]. The canes having been shredded as finely as possible, a weighed quantity is placed in any convenient extraction apparatus and thoroughly exhausted with hot water. The treatment with hot water should be continued until a few drops of the extract evaporated on a watch glass will leave no sensible residue. The residual fiber is dried to constant weight at the temperature of boiling water, cooled in a desiccator and rapidly weighed and the percentage of fiber calculated from the data obtained. On account of the great difficulty of securing a homogeneous pulp, even with the best shredding machines, the determination should be made in duplicate or triplicate and the mean of the results entered as the percentage of fiber. The term fiber as used in this sense, must not be confounded with the same term employed in the analysis of fodders and feeding stuffs. In the latter case the term is applied to the residue left after the successive treatment of the material with boiling, dilute acid and alkali. The analysis of canes for feeding purposes is conducted in the general manner hereinafter described for fodders.
216. Estimation of Sugar in Sugar Beets.—The methods employed for the determination of the sugar content of beets are analogous to those used for canes, with such variations in the method of extraction as are made possible and necessary by the difference in the nature of these sacchariferous plants. The sugar beet is more free of fiber and the hard and knotty substances composing the joints of plants are entirely absent from their composition. For this reason they are readily reduced to a fine pulp, from which the sugar is easily extracted. The analytical processes are also greatly simplified by the complete absence of reducing sugars from the juices of healthy beets. The only sugar aside from sucrose which is present in these juices is raffinose, and this is not found in healthy beets, except when they have been injured by frost or long keeping. In practical work, therefore, the determination of sucrose completes the analysis in so far as sugars are concerned. Four methods of procedure will illustrate all the principles of the various processes employed.
217. Estimation of Sucrose in the Expressed Juice.—In the first method the beets are reduced by any good shredding machine, to a fine pulp, which is placed in a press and the juice expressed. In this liquor, after clarification with lead subacetate, the sucrose is determined by the polariscope. The methods of measuring, clarifying and polarizing are the same as those described for saccharine juices in paragraphs [83-85]. The mean percentage of juice in the sugar beet is ninety-five. The corrected polariscopic reading obtained multiplied by 0.95 will give the percentage of sugar in the beet.
Example.—The solids in a sample of beet juice, as measured by a brix spindle, are 17.5 per cent. Double the normal weight of the juice is measured from a sucrose pipette, placed in a sugar flask, clarified, the volume completed to 100 cubic centimeters, the contents of the flask well shaken and filtered. The polariscopic reading obtained is 29°.0. Then (29.0 ÷ 2) × 0.95 = 13.8 = percentage of sucrose in the beet.
218. Instantaneous Diffusion.—In the second process employed for determining the sugar content of beets, the principle involved depends on the use of a pulp so finely divided as to permit of the almost instant diffusion of the sugar present throughout the added liquid. This diffusion takes place even in the cold and the process thus presents a convenient and rapid method for the accurate determination of the percentage of sugar in beets. The pulping is accomplished by means of the machine described on [page 10], or the one shown in [Fig. 67]. The beet is pressed against the rapidly revolving rasp by means of the grooved movable block and the finely divided pulp is received in the box below. These machines afford a pulp which is impalpable and which readily permits an almost instantaneous diffusion of its sugar content.