4 BULLETIN 1475, U. S. DEPARTMENT OF AGRICULTURE 
recover as much as possible of the fat. Instead of heating hog fat 
in steam- jacketed kettles, some lard makers cook it under pressure 
with live steam in closed tanks. This gives what is known in the 
trade as steam lard, in contradistinction to kettle-rendered lard. 
Bleached, deodorized oils are desirable for making: lard substi- 
tutes. The caustic soda refined oil is heated with fuller's earth, 
activated carbon, or a mixture of the two, depending upon the oil 
to be bleached, and filtered through filter presses. Then it is placed 
in a vacuum kettle and deodorized by superheated steam, which is 
blown through until the odor or flavor is removed. 
During the last 15 or 20 years large quantities of oils have been 
converted into solid products by a process known as hydrogenation. 
In this hardening process specially prepared nickel powder is used 
to effect the combination of hydrogen gas and the liquid giycerides. 
The hydrogen unites with the olein of the oil, changing" it into 
stearin, which is solid at ordinary temperatures. At the end of 
the process the nickel is removed by filtration while the oil is still 
hot. A substance which, like the nickel in this case, assists the 
combination of one substance with another, hydrogen and olein 
here, but does not itself unite with the final product, is called a 
catalyst. Great quantities of hydrogenated or hardened oils are used 
in the manufacture of lard substitutes, margarine, and soap. Dur- 
ing hydrogenation whale and fish oils lose their fishy odor and taste. 
In some countries hydrogenated whale oil is used in making mar- 
garine. 
Red oil, or commercial oleic acid, is obtained by chilling mixtures 
of fatty acids u»til the palmitic and stearic acids have crystallized. 
The solid acids are separated from the red oil by filtration and 
pressing. The composition of both the red oil and the solid acids 
depends upon the source of the mixed fatty acids. Some red oils 
are chiefly oleic acid with small quantities of dissolved palmitic 
and stearic acids: others contain notable quantities of linolic acid. 
With few exceptions the solid acids are sold as commercial stearic 
acid and are used in the manufacture of candles and soap. Red oil 
goes chiefly into textile soaps and sulphonated red oils (p. 18). 
Greases, or inedible fats, obtained in meat-packing and rendering 
plants are graded and sold on the basis of color and percentage of 
fat present. Most of the grease produced and that recovered from 
tankage and garbage, after suitable treatment, are used in making 
soap or lubricants. 
Vegetable waxes are widely distributed, but with few exceptions 
they occur only in very small quantities. Wax serves as a protec- 
tive coating for the leaves, stems, and seeds of many plants. Un- 
like the oils or fats, waxes of either animal or vegetable origin are 
not composed of giycerides. They contain fatty acids in combina- 
tion with what are known as higher alcohols. When separated in 
a pure condition these alcohols are white solids. 
VEGETABLE OILS 
COTTONSEED OIL 
Cottonseed oil is obtained from the seeds of the cotton plant, 
which is cultivated throughout large areas of the southern United 
States. Although the composition of the cottonseed depends upon 
