36 BULLETIN 867, U. S. DEPARTMENT OF AGRICULTURE. 
somewhat limited and at the same time the price materiaily higher 
than that of high-grade mineral oil it was found that the latter can 
be used in ordinary types, while only the former can be used in the 
rotary types. Abroad, however, castor oi! was used almost exclu- 
sively in all kinds of aviation motors. The reason given was that 
castor oil keeps its viscosity better, sticks better, and protects the 
cylinder walls, valve seats, and other parts. A mixture of mineral 
and castor oils, containing a preponderating percentage of the latter, 
has been universally used in stationary motors. Some trouble with 
foreign castor oil has been due to its tendency to gum, which has 
been minimized by mixing it with various proportions of heavy 
mineral oil. Great difficulty has been experienced in forming a homo- 
geneous and suitable mixture of castor and mineral! oils, owing to 
the fact that both are apparently homogeneous at the time of mak- 
ing, but separation occurs upon long standing. A patent has been 
taken out by Archbutt and Deeley for heatimg castor oil in an auto- 
clave at 260° to 300° C., under pressure of 4 to 6 atmospheres for 
about 10 hours, whereby it becomes miscible with mineral! oil in any 
proportion. Some state that castor oi! unduly precipitates carbon 
on the walls of gas-engine cylinders, owing to incomplete combustion, 
while others claim that because castor oil burns without a smoky 
flame and gasoline burns with a conspicuous cloud, any carbon 
deposited on the cylinder walls is derived from the gasoline rather than 
from the oil. 
Some lubricating engineers claim that the high steam pressures 
occurring in steam cylinders afford ideal conditions for saponifying 
eastor oil, stating that this increases the acidity of-the oil, with con- 
sequent pitting of the walls. Others claim that the walls remain 
perfectly bright. Another quality of castor oil as a lubricant, which 
seems to be quits generally accepted, is its ability to stick to the 
exposed surfaces, with consequent protection. Castor oil also keeps 
its viscosity better under changes of temperature than any other 
vegetable oil and many mineral oils. 
Artificial leather is made by dissolving cellulose nitrates in volatile 
solvents, incorporating castor oil in the mixture and distributing the 
same over treated cloth. Upon volatilization of the solvent, the solid 
constituents remain fixed on the goods. The réle of the oil is to 
impart softness and elasticity to the otherwise hard and stiff product 
and to enable this to be more readily coated on the cloth or other 
backing material. There are very few oils which can be added to 
nitrocellulose solutions without either causing the separation of the 
nitrocellulose from the solution or spoiling the luster and cohesion of 
the film. It is evident that a nondrying oil must be used and also 
one that is perfectly miscible in the solvents used. Castor oil fulfills 
these conditions very satisfactorily and is of additional value on 
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