( 4 ) 
kernels or copra, or where the oil content of the 
seed is low, as in the case of cotton seed. In such 
cases, therefore, after leaving the crushing rolls, 
the meal is heated and pressed direct. 
THE presses employed in modern oil expression 
practice are of the hydraulic type; they vary in 
design, the two chief types being the Anglo-American 
open press, and the closed cage press. 
There are also machines in use called “ expellers ” 
which are designed to combine both the crushing 
and the preliminary pressing. These machines work 
on the principle of a screw conveyor, the raw 
material being fed through a hopper at one end and 
being forced out at the other through the annular 
space between the screw and the outer casing. 
IN the second process the oil is extracted from the 
meal by means of hot or cold chemical solvents. 
The chief solvents in use are carbon bisulphide, 
benzene, carbon tetrachloride and trichloroethylene. 
Briefly, the process consists in allowing the hot or 
cold solvent to percolate through the meal contained 
in a series of closed vessels, when the solvent will 
dissolve out the oil. The solution is then transferred 
to a heated still in which the solvent is distilled 
off, leaving the oil behind. The solvent can be 
recovered and used again. 
These two are not necessarily rival processes but 
are worked together, sometimes in the same mill. 
Thus, certain seeds can be crushed cold in order to 
obtain a high-class edible oil, and then treated by 
a solvent extraction process to recover the remainder 
of the oil, since with the latter process it is possible 
