10 BULLETIN 769, U. S. DEPARTMENT OF AGRICULTURE. 
of fuller's earth, which takes up a large part of the remaining color 
not removed by the caustic soda, or other alkali. The fuller's earth, 
with the color which it has absorbed, is then filtered out from the 
oil by forcing the mixture through a filter press. 
In making lard substitutes it is desirable to use a very bland oil, 
that is, one possessing but little odor or flavor. To produce such an 
oil, the refined and bleached oil must be subjected to a third process, 
that of deodorizing. As a rule, this consists merely in blowing 
superheated steam through the oil which is heated in a vacuum 
kettle. Recently hydrogen has been substituted for steam, and by 
its use it is now practicable to deodorize even the fish oils. 
A very interesting method for converting liquid oils into solid fats 
which has recently come into rather general use is known as hydro- 
genation. In this hardening process reduced nickel is employed to 
effect the combination of hydrogen gas and the liquid glycerids. 
The hydrogen unites with the oleins of the oil, changing them into 
stearins, which are solid at ordinary temperatures. The nickel does 
not combine with the oil, or at least not permanently, and at the end 
of the process can be removed by filtration and used again. A sub- 
stance that acts in this way, simply to collect, as it were, one chemical 
substance and pass it along, and force its acceptance upon another 
substance, is termed a catalyst. 
HOW TO SAFEGUARD OUR OIL AND FAT SUPPLY. 
So much for a brief description of the general processes used in 
the production of our fats and oils. Now let us consider the possi- 
bilities for increasing our supplies of the various food and technical 
oils. How can we develop new sources of these most important 
substances ? In what ways can we improve upon our present methods 
of manufacture? How can we substitute the more abundant oils 
for those which are scarce, and how conserve for the purposes to which 
they are peculiarly adapted those oils, which, like castor oil as a 
lubricant for aeroplane engines, can not easily be replaced by other 
oils? 
VEGETABLE OILS. 
COTTONSEED OIL. 
From the data in Tables 1 and 2 it is apparent that the United 
States produces more cottonseed oil than any other single oil — 
nearly 1,344,000,000 pounds during the calendar year 1917. We 
likewise consume more of this oil than of all other vegetable oils 
combined. This is due not only to its suitability for both table and 
cooking purposes, but also to the fact that it forms the bulk of the 
lard substitutes, and that large amounts are employed in the manu- 
facture of oleomargarine, as well as in soap and other technical 
industries. 
