PRODUCTION AND UTILIZATION OF FATS AND OILS 23 
per bushel of seed. The press cake usually contains 6 to 8 per cent 
of oil. 
The hot-pressed oil contains some mucilaginous matter extracted 
from the seed, which must be removed from oil designed for certain 
technical purposes. When the oil is stored for a long time, the 
mucilaginous substances separate and gradually settle. A more 
rapid method, which has been in use for many years, consists in treat- 
ing the oil with 1 or 2 per cent of sulphuric acid. This chars the 
impurities and causes them to separate from the oil. As linseed oil is 
easily damaged by using too highly concentrated acid, this method 
requires care and experience. Increasingly large quantities of the 
oil are being refined by the caustic-soda process in a manner similar 
to that employed for treating crude cottonseed oil (p. 6). This 
yields a product of great purity. 
Linseed oil can be bleached by exposure to the sun, by treatment 
with benzoyl peroxide, dichromates, hydrochloric acid, ozonized air, 
and fuller's earth, and by blowing air through the heated oil. Ke- 
nning by the sulphuric- acid and caustic-soda methods also removes 
a large part of the coloring matter present in the crude oil. 
Boiled linseed oil is now generally prepared by heating the oil in 
steam-heated kettles with organic or inorganic compounds of lead, 
manganese, or cobalt, known as driers. The cost of producing this 
boiled oil is smaller than that of boiling over a direct fire, as was 
formerly done. To produce the light-colored oils air is passed 
through the heated oil. Boiled oil is sold as double-boiled, single- 
boiled, pale-boiled, extra pale, and bleached-boiled oil, and by various 
other trade names indicating differences in color, consistency, and 
drying properties. 
Blown linseed oil is prepared by passing air through the heated 
oil until the desired viscosity is reached. In this process it is 
important to keep the oil at about 250° F., as a higher temperature 
impairs the color. Driers like cobalt linoleate should be added to 
the oil after it has cooled below 150° F. Blown oil of a light color 
is necessary for use in making special paints, varnishes, and enamels. 
Stand linseed oil is made by heating thoroughly settled or re- 
fined oil in varnish kettles to about 550° F. and keeping it at this 
temperature until the desired viscosity is obtained. Aluminum 
kettles give the lightest-colored product. 
Uses 
In Kussia, Hungary, Germany, and India large quantities of 
cold-pressed linseed oil are used for edible purposes. Hot-pressed 
oil is employed for technical purposes only, chiefly in the manufac- 
ture of paints, varnishes, enamels, linoleums, printing ink, and soft 
soap. Stand linseed oil is used in the manufacture of air-drying and 
baking enamels, and also as a lithographic oil for copper-plate 
printing. 
CHINA-WOOD OR TUNG OIL 
China-wood or tung oil is obtained from two species of Aleurites. 
a small genus belonging to the Spurge family. About 90 per cent of 
the oil produced in China comes from the seeds or nuts of the 
Aleurites fordii, which, being more hardy than the other species 
