[165] Foods, Their Composition and Analysis, p. 139. [166] Richardson, Vid. op. cit. 142, p. 158. [167] Principal Starches used as Food, Cirencester, Baily & Son, Market Place. [168] Vid. op. cit. 142, pp. 158 et seq. [169] Bulletin 44, Department of Agriculture, Division of Chemistry, p. 14. PART THIRD. PROCESSES FOR DETECTING AND DETERMINING SUGARS AND STARCHES AND OTHER CARBOHYDRATES IN CRUDE OR MANUFACTURED AGRICULTURAL PRODUCTS. =203. Introduction.=—In the preceding part directions have been given for the estimation of sugars and starches in approximately pure forms. In the present part will be described the most approved methods of separating these bodies and other carbohydrates from crude agricultural products and for their chemical examination. In many respects the processes which in a small way are used for preparing samples for analysis are employed on a large scale for technical and manufacturing purposes. It is evident, however, that the following paragraphs must be confined strictly to the analytical side of the question inasmuch as anything more than mere references to technical processes would lead into wide digressions. In the case of sugars the analyst is for the most part quite as much in need of reliable methods of extraction and preparation as of processes for analysis. With starches the matter is more simple and the chief methods of separating them for examination were necessarily described in the previous part. Sugars in fresh plants exist almost entirely in solution. This is true of all the great sources of the sugar of commerce, _viz._, the palm, the maple, the sugar beet and sugar cane. This statement is also true of fruits and the natural nectar of flowers. By natural or artificial drying the sugar may be reduced to the solid or semisolid state as in the cases of raisins and honey. In certain seeds, deficient in water, sugars may possibly exist in a solid state naturally, as may be the case with sucrose in the peanut and raffinose in cotton seed. Starches on the other hand when soluble, are probably not true starches, but they partake more or less of a dextrinoid nature. Fine starch particles occur abundantly in the juices of some plants, as for instance sorghum, where they are associated with sugar and can be obtained from the expressed juice by subsidence. But even in such a case it is not certain that the starch enters into the general circulation. It is more likely formed locally by biochemical condensation of its constituents. Starches in a soluble or semisoluble state are transported, as a rule, to the tubers or seeds of plants where they are accumulated in large quantities as a reserve food for future growth. For a study of the plant metabolism whereby starch is produced and for its histological and physiological properties the reader may consult the standard authorities on vegetable physiology.[170]