SEED OILS 89 
’ 
tically prevented. This is especially true of coconut oil, as 
Walker * has shown. Edible oils which are rancid and have a 
high acidity are not suited for edible purposes. Such oils are 
used largely for soap making. Since edible oils command a 
much higher price than soap oils, it is evident that when edible 
oils are allowed to become rancid the oil producer suffers con- 
siderable loss. 
Investigation has shown that each particular oil has certain 
definite physical and chemical constants such as specific gravity, 
refractive index, saponification value, iodine value, etc. For a 
given oil, the exact value of these constants would naturally be 
affected by the purity of a particular sample and perhaps other 
factors. The results obtained by determining these various con- 
stants (oil analysis) are very useful in ascertaining the purity 
of a particular sample of a known oil or in endeavoring to iden- 
tify an unknown one. 
Lewkowitsch,+ Allen,t Mitchell,§ Woodman,|| and various 
other authorities give explicit directions for making oil anal- 
yses and explain how the results may be interpreted. 
In recent years the demand for edible oils has been steadily 
increasing. As a result of this tendency, efforts have been made 
to convert oils formerly used for making soaps and candles into 
edible oils, which are considerably more valuable. For this pur- 
pose the method which has proved most successful is known as 
hydrogenation. This process consists in converting fatty oils, 
which are liquid at ordinary temperatures, into hard, solid fats. 
The liquid fats consist largely of olein, which is a combination 
of oleic acid and glycerol (oleic glyceride) ; solid fats consist 
largely of stearin, a combination of stearic acid and glycerol 
(stearic glyceride). The glycerides comprising the hard por- 
tion of an oil contain more hydrogen than those forming the 
soft portion. It is possible, then, to harden the soft portion 
by merely adding a small amount of hydrogen, which is a well- 
known chemical gas. The hydrogenation process has been used 
successfully for preparing oils suitable for the soap and candle 
industries and also for making edible oils. Not only are soft 
oils hardened by hydrogenation, but certain of their oil constants 
* Walker, H. S. The keeping qualities and the causes of rancidity in 
coconut oil. Philippine Journal of Science, Section A, Volume 1 (1906), 
page 117. 
+ Lewkowitsch, J. Oils, fats, and waxes. (1915), Volume 1. 
+ Allen, Commercial organic analysis. (1910), Volume 2. 
§ Mitchell, C. A. Edible oils and fats, (1918). 
|| Woodman, A. G. Food analysis, (1915). 


