FATS AND THEIR ECONOMICAL USE IN THE HOME. 15 
sibflities owing to the fact that as a result of a long series of labora- 
tory experiments processes have been discovered by which oils may 
be transformed into a product of any desired hardness by chemically 
adding hydrogen to them. This reaction takes place, for instance, 
when finely divided nickel, hydrogen, and the oil to be hardened 
are intimately mixed under proper conditions. The nickel does not 
enter into the composition of the hardened fat, but is removed and 
used repeatedly in the preparation of other batches. The hard- 
ened oils are generally white in color, have no appreciable odor or 
taste, and are less likely to become rancid than the original oil. 
A number of these fats, marketed under a variety of trade names, 
have proved popular and appear to be of quite wide application. 
This hardening process may also be of special value in the future 
utilization of some oils like the fish oils, which, because of objection- 
able flavors and odors, are not entirely suited for edible purposes in 
their natural state. 
NUT BUTTERS. 
Closely related to the nut oils mentioned above (see p. 13) are 
the nut butters prepared by grinding finely the meats of peanuts, 
almonds, or other nuts rich in fat, so as to produce an oily mass 
much like butter in consistency. Peanut butter is by far the most 
common of the nut butters. It is used chiefly as a filling for sand- 
wiches, crackers, etc., though it finds some use in cooking. The nut 
butters can be made at home by grinding the whole nuts; a special 
nut-butter knife being furnished with some of the meat or food 
choppers. In addition to containing a large amount of fat, nut 
butters also contain considerable protein. 
AVOCADO. 
Although its oil is not extracted for food purposes, the avocado, 
commonly called the alligator pear, a tropical fruit which is becom- 
ing better known in some of our markets, contains as high as 20 per 
cent of fat in the edible portion. When used in the diet this must be 
taken into consideration as a source of fat. 
THE SELECTION OF EDTBLE FATS. 
In the selection of edible fats the principal considerations should 
be the purpose for which the fat is to be used, quality, price, and 
individual preference, since the energy which the body derives from 
different fats is about the same, and all are regarded as wholesome 
when of good quality. Custom, which influences to a considerable 
extent the choice of all foods, can, therefore, be subordinated to the 
more essential consideration of economy. 
