CARBOHYDRATES 31 



remain a small quantity of ash or mineral matter, varying 

 somewhat in the different kinds of cereals as shown in the 

 chart. Upon further analysis this ash is found to consist of 

 certain earthy substances (potash, lime, magnesia, soda, and 

 silica) variously combined with phosphorus, sulphur, and 

 oxygen. It is important to remember that such substances 

 form the princijoal constituents of bones and teeth, and that 

 cereals are particularly rich in the mineral matters specially 

 required for building these hard parts of our bodies. 



28. Nutrients. A large part of the grain consumed in 

 burning, consists of nutrients, i. e., nutritious substances, 

 which form the main bulk. Besides this there is a small 

 amount of woody material (non-nutrient) contained chiefly 

 in the hull. When this indigestible covering is removed in 

 the process of milling, the meal or flour which is left, repre- 

 sents therefore the nutritive part of the grain free from 

 nearly all that is useless for food. Plainly, then, it is upon the 

 composition of this inner part that the value of the grain 

 must principally depend; and here, as we shall see, the most 

 important differences are to be found. 



29. Carbohydrates. If we knead a little wheaten dough 

 in a considerable quantity of water, the latter becomes milky 

 from the presence of a pure white substance which washes out 

 from the dough, while there is left behind a curious, elastic, 

 pale-colored mass sometimes called "wheat gum." 



If we allow the milky water to stand for some time, a 

 large part of the white substance will settle, thus showing 

 that it is a fine powder which was merely suspended in the 

 water, and not really dissolved. This white material is 

 starch, as maj' be proved bj' adding to some of it a little 

 iodine solution; this will turn it a dark bluish color, and 

 starch is the only substance known to be thus affected. 



If starch be boiled with a dilute acid for a sufficient time 

 it becomes mainly converted into a kind of sugar known 

 as glucose, or grape-sugar, an important constituent of the 

 commercial "glucose" of which large quantities are used 

 in confectionery. Chemistry teaches us that this change is 

 made possible by the fact that both starch and glucose con- 

 sist of the same elements, — namely, carbon, hydrogen, and 



