PRODUCTION AND UTILIZATION OF FATS AND OILS 6 
ing expellers. Nowadays, particularly in Europe, large quantities 
of oils are extracted by the use of volatile solvents, such as gasoline 
and benzene. Olives, peanuts, and sesame seed are pressed cold, pro- 
ducing what is known as virgin or cold-pressed oils. As a rule, cold- 
pressed oils need only to be filtered to make them suitable for edible 
purposes. Most oil seeds in the United States are heated and 
pressed hot, because it is possible to obtain more oil by hot than by 
cold pressing. In many instances cold pressing is followed by one 
and sometimes more hot pressings. The hot-pressed and solvent- 
extracted oils contain coloring and flavoring substances, which are 
removed by refining before the oil is used for food or even, in many 
cases, for technical purposes. 
The residue from pressing, which contains 5 to 12 per cent of oil, 
depending upon the character of the product pressed and the equip- 
ment used, is called press or oil cake. When not poisonous, it is with 
few exceptions converted into feed for livestock. Inedible or poison- 
ous press cakes are used for fertilizers. When ground the press cake 
is called a meal. The residue from the solvent extraction of an oil, 
known as extracted meal, contains less than 2 per cent and fre- 
quently not more than 1 per cent of oil. It may be used for the same 
purposes as press cake. If used for feed, however, all of the solvent 
must be removed. 
Nearly all hot-pressed oils are refined before being used. The 
most common method is to treat the warm oil with a solution of 
caustic soda (sodium hydroxide), which neutralizes the free fatty 
acids to form soap and precipitates much of the coloring matter. 
After further agitation and heating to the proper degree the soap 
separates from the oil in small soft aggregates. This stage of re- 
fining is called the break. On standing, the soap settles to the 
bottom of the refining kettle to form the soap stock, which is used 
by soap makers. At some plants the soap stock is acidified with 
sulphuric acid to set free the fatty acids, which, with the neutral oil 
occluded in the soap stock, rise to the surface and are removed. 
This is sold as acidulated soap stock. 
In the larger refineries it is customary to separate the fatty acids 
from the soap stock and after suitable treatment to distill them 
under diminished pressure. The distilled fatty acids are used by 
candle and soap makers. The residue in the still after distillation is 
known as pitch. The product obtained by the distillation of cotton- 
seed oil fatty acids, called cotton oil or stearin pitch, is employed, 
for one thing, in the manufacture of roof paint. 
The term foots, sometimes used in place of " soap stock," is not to 
be confused with the term " olive oil foots," the name given to the 
low-grade olive oil extracted by solvents from the olive pomace or 
press cake. Olive oil foots is sometimes called sulphur olive oil, be- 
cause it is largely extracted by carbon disulphide. The term foots 
is applied also to the settlings, which are allowed to separate in the 
settling tanks at crude oil mills before the oil is shipped to the 
refinery. 
To obtain most animal fats or oils, the tissues in which they exist 
are cut in pieces and rendered or tried; that is, heated until the 
melted product separates. After the separated fat has been with- 
drawn, the cracklings, or cooked tissues, are usually pressed to 
