re is about 44 per cent of
carbon, while in fat there is 75 per cent. Hence it is that when fat is
burned or undergoes combustion, it yields a larger amount of the
products of combustion--carbon dioxid and water--than does starch. A
gram of fat produces 2-1/4 times as much heat as a gram of starch. Fat
is the most concentrated non-nitrogenous nutrient. As found in food
materials, it is a mechanical mixture of various fats, among which are
stearin, palmitin, and olein. Stearin and palmitin are hard fats,
crystalline in structure, and with a high melting point, while olein is
a liquid. In addition to these three, there are also small amounts of
other fats, as butyrin in butter, which give character or individuality
to materials. There are a number of vegetable fats or oils which are
used for food purposes and, when properly prepared and refined, have a
high nutritive value. Occasionally one fat of cheaper origin but not
necessarily of lower nutritive value is substituted for another. The
fats have definite physical and chemical properties which enable them to
be readily distinguished, as iodine number, specific gravity, index of
refraction, and heat of combustion. By iodine number is meant the
percentage of iodine that will unite chemically with the fat. Wheat oil
has an iodine number of about 100, meaning that one pound of wheat oil
will unite chemically with one pound of iodine. Fats have a lower
specific gravity than water, usually ranging from .89 to .94, the
specific gravity of a fat being fairly constant. All fats can be
separated into glycerol and a fatty acid, glycerol or glycerine being
common constituents, while each fat yields its own characteristic acid,
as stearin, stearic acid; palmitin, palmitic acid; and olein, oleic
acid. The fats are soluble in ether, chloroform, and benzine. In the
chemical analysis of foods, they are separated with ether, and along
with the fat, variable amounts of other substances are extracted, these
extractive products usually being called "ether extract" or "crude
fat."[5] The ether extract of plant tissue contains in addition to fat
appreciable amounts of cellulose, gums, coloring, and other materials.
From cereal products the ether extract is largely fat, but in some
instances lecithin and other nitrogenous fatty substances are present,
while in animal food products, as milk and meat, the ether extract is
nearly pure fat.

14. Organic Acids.--Many vegetable foods contain small am