( 2 ) 
ments are at present being carried out; together 
with brief notes regarding the methods in general 
use for the extraction of oils and their industrial 
applications. 
Classification . — Before stating how oils and fats 
derived from vegetable sources are classified, it is 
perhaps necessary to state that the difference be- 
tween an oil and a fat depends solely on temperature, 
for a fat when melted is termed as oil and an oil 
when solidified becomes a fat. An instance of the 
manner in which the temperature of a climate affects 
this nomenclature is seen in the case of coconut oil, 
which in this country is a liquid and would there- 
fore be regarded as an oil, while in Northern Europe 
it is a fat. 
Oils from vegetable sources are classified as either 
fixed or essential. By the term fixed is meant an 
oil which cannot be volatilised without undergoing 
chemical decomposition, while the opposite applies 
to essential oils which are sometimes known as 
volatile oils. 
There is also a great difference, from a chemical 
point of view, between the two classes. The fixed 
oils and fats are mixtures of glycerides of fatty 
acids ; that is to say, chemical compounds formed 
by the combination of glycerine with fatty acids, 
and which yield glycerine and soap when treated 
with caustic alkalis. 
Essential oils, on the other hand, consist of mix- 
tures of highly complex organic compounds such as, 
for example, hydrocarbons (compounds of carbon 
and hydrogen), alcohols, aldehydes, and esters, 
which do not react with caustic alkalis in the same 
way as fixed oils. 
