The Romance of Modern Chemistry

 SUGAR AND STARCH formed when starch is heated either alone or with a little acid. Although dextrin has the same chemical composi- tion as starch, it gives a reddish brown colour with iodine, instead of the blue colour which is so characteristic of starch. Dextrin is applied to some curious purposes— for example, as an adhesive on envelopes and postage stamps, in giving a gloss to paper and cardboard, and in producing a head on beer and ærated liquids. The possibility of converting the various carbohydrates into glucose is further illustrated by the changes which vegetable fibre, or cellulose, may be made to undergo. This is a carbohydrate of the same chemical composition as starch, but differs from the latter in being indigestible except by herbivorous animals, which have a special apparatus for dealing with it. Cotton-wool and Swedish filter-paper are nearly pure cellulose, from which it will be obvious that this carbohydrate is not a suitable article for human food. When eaten, it simply passes through the body without being digested. Cellulose, in either of the forms just mentioned, is dissolved by strong sulphuric acid; if the solution is diluted with water, and subjected to prolonged boiling, the cellulose, like starch, only less readily, is converted into glucose. Bearing in mind that the fermentation of this sugar yields alcohol, the reader will perceive that it is actually possible to prepare spirituous liquors from linen or cotton rags, for these consist very largely of cellulose. From rags to alcohol, however, is a transformation which is a chemical curiosity rather than a practically applied process. The name “ cellulose11 suggests the commercial article known as “ celluloid,'” which is indeed derived from cellulose. In chapter xv. it was shown that when cotton-