SEPARATION AND DETERMINATION OF STARCH. =263. Occurrence.=—Many bodies containing starch are presented for the consideration of the agricultural analyst. First in importance are the cereals, closely followed by the starchy root crops. Many spices and other condiments also contain starchy matters. In the sap of some plants, for instance sorghum, at certain seasons, considerable quantities of starch occur. In the analysis of cereals and other feeding stuffs, it has been the usual custom to make no separate determination of starch, but to put together all soluble carbohydrates and estimate their percentage by subtracting from 100 the sum of the percentages of the other constituents of the sample. This aggregated mass has been known as nitrogen-free extract. Recent advances in methods of investigation render it advisable to determine the starch and pentosan carbohydrates separately and to leave among the undetermined bodies the other unclassed substances, chiefly of a carbohydrate nature, soluble in boiling dilute acid and alkali. =264. Separation of Starch.=—Starch being insoluble in its natural state, it is impossible to separate it from the other insoluble matters of plants by any known process. In bringing it into solution it undergoes certain changes of an unknown nature, but tending to produce a dextrinoid body. Nevertheless, in order to procure the starch in a state of purity suited to analytical processes, it becomes necessary to dissolve the starch from the other insoluble bodies that naturally accompany it. As has been shown in preceding paragraphs, there are only two methods of securing the solution of starch which fully meet the conditions of accurate analysis. These are the methods depending on the use of diastatic ferments and on the employment of heat and pressure in the presence of water. These two processes have been described in considerable detail in paragraphs =179-181=. It is important, in starch determinations, to remove from the sample the sugar and other substances soluble in water and also the oils, when present in large quantities, before subjecting it to the processes for rendering the starch soluble. =265. Desiccation of Amyliferous Bodies.=—The removal of sugars and oils is best secured in amyliferous substances after they are deprived of their moisture. As has already been suggested, the desiccation should be commenced at a low temperature, not above 60°, and continued at that point until the chief part of the water has escaped. The operation may be conducted in one of the ways already described (pp. 12-27). There is great difference of opinion among analysts in respect of the degree of temperature to which the sample should be finally subjected, but for the purposes here in view, it will not be found necessary to go above 105°. Before beginning the operation the sample should be as finely divided as possible, and at its end the dried residue should be ground and passed through a sieve of half a millimeter mesh.