CARBOHYDRATES dl 
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 principal 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, 7. 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 may be proved by 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 
