2 BULLETIN 1475, U. S. DEPARTMENT OF AGRICULTURE 
Substances belonging to several distinct groups are termed oils. 
Mineral oils, which include the petroleum and shale oils, are known 
also as hydrocarbon oils because they are composed chiefly of mix- 
tures of substances which are chemical combinations of carbon and 
hydrogen. Oils of another group obtained by the destructive distil- 
lation of coal tar consist chiefly of a mixture of hydrocarbons and 
phenols. The so-called carbolic acid is an example of this group. 
Odoriferous oils, which are obtained by distillation with steam or 
by pressure from leaves, stems, flowers, seeds, roots, and bark of 
plants, and from the skins of citrus fruit, are known as volatile or 
essential oils. These are usually complex mixtures of substances 
known to the chemist as terpenes, aldehydes, ketones, alcohols, 
phenols, and esters (chemical combinations of acids with alcohols). 
Most of them are liquid, but some are semisolid or solid. The sub- 
stances discussed in this bulletin are called fixed or fatty oils and 
fats to distinguish them from the volatile or essential oils. 
There is no distinct chemical difference between a fat and a fatty 
oil. Each is composed chiefly of glycerides, substances formed by 
the combination of fatty acids with glycerine. Products which are 
liquid at ordinary temperatures are termed oils. Those which are 
solid at ordinary temperatures are commonly called fats. Some of 
the oils obtained from fruits and seeds are not liquid, but are either 
solid fats or butters, like cacao butter. On the other hand, lard, 
tallow, and other land-animal fats are more or less solid at ordinary 
temperatures. The fats or oils from fish, whales, and almost all 
other marine animals are liquid. 
For convenience, the fats and oils considered in this bulletin may 
be divided into three general classes: Drying, semidrying, and non- 
drying. This classification is based upon the capacity for absorp- 
tion of oxj^gen (both rate and quantity). These classes are not 
sharply defined, the oils of one class gradually merging into those 
of the next class. The oils which rapidly absorb oxygen and form 
solid films, such as linseed, China-wood or tung, perilla, and men- 
haden oils, are classed as drying oils. Oils of the semidrying class 
absorb oxygen less rapidly than the drying oils. This class includes 
cottonseed, corn, sesame, and mustard-seed oils. The nondrying oils 
absorb oxygen very slowly. To this class belong the land-animal 
fats and olive, castor, peanut, coconut, and palm oils. 
In the following pages the more important edible vegetable oils 
are treated first in the order of their importance, irrespective of the 
class to which they belong. The less important edible and technical 
vegetable oils come next. The vegetable drying oils, with the excep- 
tion of soy-bean and sunflower-seed oils, have been grouped together. 
Then follow the land-animal fats, fish and marine-animal oils, and 
the waxes. 
GENERAL METHODS OF PRODUCTION 
The profitable production and refining of fats and oils require an 
intimate knowledge of the raw materials and details of manufacture, 
which can be mastered only through experience, and also a knowl- 
edge of market conditions for both the raw materials and the finished 
products. 
Vegetable oils are commonly expressed from the seeds or fruit 
containing them, either by hydraulic presses or by continuous work- 
