the saponification, or hydrolysis, of natural fats
and oils which, as has been shown, are mixtures of many glycerides, the
resultant soaps, or fatty acids, are mixtures of as many compounds as there
were individual glycerides of the original fat, but the glycerol is
identical in every case.

When glycerol is heated with dehydrating agents, it is easily converted
into _acrolein_, an unsaturated aldehyde having a peculiar characteristic
pungent odor. Hence, the presence of glycerol, or glycerides, in any
substance may usually be detected by mixing the material with anhydrous
acid potassium sulfate and heating the mixture in a test tube, when the
characteristic odor of acrolein will appear.

Glycerol possesses all the characteristic properties of an alcohol, forming
alcoholates with alkalies, esters with acids, etc. It is an active reducing
agent, being itself easily oxidized to a variety of different products
depending upon the strength of the oxidizing agent used and the conditions
of the experiment. Microorganisms affect it in a variety of ways, either
converting it into simple fatty acids, or condensing it into longer-chain
compounds.

=Open-chain monohydric alcohols=, higher members of the ethyl alcohol
series, such as cetyl, C_{16}H_{33}OH, carnaubyl, C_{24}H_{49}OH, ceryl,
C_{26}H_{53}OH, and melissyl, C_{30}H_{61}OH, are found in the esters which
constitute the major proportion of the common waxes.

=Cholesterol and phytosterol= are empirical names for certain closed-ring,
monohydric alcohols which are found in relatively small amounts in all
fats, the former term designating those found in animal fats and the latter
those of plant origin. Their composition has not yet been definitely
established. They are known to contain two, or three, closed rings,
probably of the phenanthrene type; to form dichlor- and dibrom- addition
products, showing that they contain one side-chain double linkage; and to
yield ketones when oxidized, indicating that they are secondary alcohols.
They form acetyl esters, or acetates, which can be separated from each
other and identified by their crystal forms and melting points. Because of
this fact and of the further fact that they are present in detectable
quantities in practically all fats and oils, they afford a qualitative
means of distinguishing between fats of animal and of plant origin. This
possibility is the most interesting fact known concerning these complex
alcohols; although t