The Romance of Modern Chemistry

SUGAR AND STARCH mostly starch; in addition, there is about 15 per cent, of water and a little mineral ash. As another example of a common food, we may take potatoes, which contain 75 per cent, of water, 21 per cent, of carbohydrates, and 2 per cent, of proteids; they contain only a trace of fat. The pea differs from the potato in having a relatively large proportion of nitrogenous substances—as much as 22 or 23 per cent.—while the carbohydrates amount to about half the weight of the pea. Cheese, again, is a case of a food containing very little carbo- hydrate and a high proportion of proteid; an average composition is 34 per cent of water, 28 per cent, of proteid, S3 per cent, of fat, and 2 per cent, of carbo- hydrate. As opposed to these mixed food-stuffs, sugar is a pure carbohydrate, and butter is practically nothing but fat with an admixture of water. All carbohydrates are ultimately obtained from the vegetable kingdom, and of the numerous substances which belong to this class, none is better known than sugar. It must, however, be pointed out at once that the meaning which the ordinary person attaches to “sugar” is not quite what the scientist understands by it The chemist speaks of “ sugars,” for there are several distinct substances known to him which go under this name; there are, for instance, cane sugar, milk sugar, malt sugar, and grape sugar or glucose. To these the reader might be inclined to add beet sugar, but this would be a mistake. The substances just mentioned are indeed named from their different sources, but it is not on that account that they are regarded as distinct members of the sugar class. Investigation has shown that they are chemically different; even although in some cases the proportions of carbon, hydrogen, and oxygen are equal, the arrange- 228