36 BULLETIN 867, U. S. DEPARTMENT OF AGRICULTURE. 



somewhat limited and at the same time the price materially 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 oil 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 heating 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 oil 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 

 castor 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 quite 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 role 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 



