ents carbon, hydrogen, and
oxygen. Sugars used for household purposes are derived mainly from the
sugar cane and the sugar beet.[25] At the present time about two fifths
are obtained from the cane and about three fifths from the beet. When
subjected to the same degree of refining, there is no difference in the
chemical composition of the sugars from the two sources; they are alike
in every respect and the chemist is unable to determine their origin.
The production of sugar is an agricultural industry; the methods of
manufacture pertain more to industrial chemistry than to the chemistry
of foods, and therefore a discussion of them is omitted in this
work.[26]

[Illustration: FIG. 15.--SUGAR CRYSTALS.]

74. Commercial Grades of Sugar.--Sugars are graded according to the
size of the granule, the color and general appearance of the crystals,
and the per cent of sucrose or pure sugar. Common granulated sugar is
from 98.5 to 99.7 per cent pure sucrose. The impurities consist mainly
of moisture and mineral matter. In the process of refining, sulphur
fumes are frequently used for bleaching and clarifying the solution.[26]
The sulphurous acid formed is neutralized with lime, which is rendered
insoluble and practically all removed in subsequent filtrations. There
are, however, traces of sulphates and sulphites in ordinary sugar, but
these are in such small amounts as not to be injurious to health. When
sugar is burned, as in the bomb calorimeter, so as to permit collection
of all of the products of combustion, granulated sugar yields about 0.01
of a per cent of sulphur dioxid.[13] Occasionally coloring substances,
as a small amount of indigo, are added to yellow tinged sugars to impart
a white color, much on the same principle as the bluing of clothes. The
amount used is usually extremely small, and the effect on health has
never been determined. Occasionally, however, bluing is used to such an
extent that a blue scum appears when the sugar is boiled with water.
Sugar has high value for the production of heat and energy. Digestion
experiments show that when it is used in the dietary in not excessive
amounts, it is directly absorbed by the body and practically all
available. It can advantageously be combined with other foods to form a
part of the ration.[27] When a ration contains the requisite amount of
protein, sugar is used to the best advantage. Alone it is incapable of
sustaining life, because it does not contain any nitroge