28 BULLETIN 769, U. S. DEPARTMENT OF AGRICULTURE. 
known all the linseed oil we now produce is either hydraulic or 
expeller, sometimes called " cold-pressed," oil. 
Flax seed averages about 35 per cent oil, the press cake usually 
containing between 6 and 8 per cent of oil, with some loss in milling 
and cooking. The average American yield is about 16 pounds of oil 
and 36 pounds of cake per bushel of seed, or an oil production of 
approximately 27 per cent. As already stated, linseed oil is not 
looked upon in the United States as a food oil, but since it can be 
made palatable by the proper refining and deodorizing treatment, 
we might fall back upon it in case of a serious food oil shortage. 
HOW TO INCREASE THE SUPPLY. 
The opportunities mentioned in connection with cotton seed 
crushing exist for increasing the yield of oil from flax seed. "New 
process" mills might be built or gasoline extraction plants established 
at the existing hydraulic mills to extract the press cake and recover 
the residual oil contained in it. This country could produce a larger 
supply of linseed oil by raising more flax, and efforts have been made 
by the Department of Agriculture and the experiment stations in 
flax-growing States to supply proper seed and have a greater acreage 
planted. As the 1918 crop in North America fell short of our require- 
ments, owing to dry weather in June and July, it is fortunate that 
a few years ago when the price of linseed oil was abnormally high, 
the paint manufacturers and the Department of Agriculture made 
an investigation of possible substitutes for this product. 
SUBSTITUTES. 
In addition to corn, soy bean, perilla and fish oils, tung, China wood, 
or Chinese nut oil, as it is variously known, can be used in place of 
linseed oil in paints, varnishes, and other manufactured products. 
With the exception of tung and probably perilla oils, none of these 
apparently dry with the tough skin that is essential for a good, 
lasting paint oil, and they do not make varnishes that are at all 
satisfactory. Corn oil, however, makes perhaps a better rubber 
substitute than linseed, and in linoleums it and fish oil have been 
used to some extent. For certain kinds of rosin varnishes, those 
that are not affected by water, tung oil has been claimed to be even 
superior to linseed oil (p. 31). 
CASTOR OIL. 
DOMESTIC AND FOREIGN CASTOR BEAN PRODUCTION. 
To most of us the term castor oil at once brings to mind a nauseous 
medicine. Few are aware that it is at present almost an absolute 
necessity for our high-speed airplane motors. And where to get 
enough of this oil for the airplane squadrons we were equipping, to 
