526 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



5. The oil must not have been treated with sulphuric or other 

 acids, as is the case Avith refined rape oil, or deodorized heavy 

 kerosene; besides the injurious effects of the accidental remnant 

 of those acids on the metal, the lubricating smoothness of the oil 

 is destroyed, it feels rough between the fingers, and does not 

 diminish the friction as much as the same oil not treated with 

 acids, as I prove by experiment. 



6. It must be pure and perfectly transparent, and contain no 

 gritty, earthy, or mineral n)atter which will attack the machinery, 

 as is the case with crude petroleum, of which the heavy black 

 variety is now extensively sold as a lubricator, and may do well 

 enough for coarse machinery, but contains a very fine grit, Vihe 

 polishing powder, and is not to be recommended for locomotives 

 and similar valuable machinery. The same may be said of the 

 tar left from the distillation of light petroleum, in which the natu- 

 ral lubricating parts of the petroleum are mostly destroyed, l)urned 

 away, and which contains fine free carbon in suspension ; this tar 

 being too thin, is melted together with common rosin to thicken 

 it, and sold as a superior wagon grease, which by the way it is not; 

 its only virtue is that it is very cheap. About the transparency 

 spoken of under this head, 1 will still remark that the color is of 

 no importance ; the light colored oil is not better than the dark 

 red ; I have even found that all attempts at giving oil a very light 

 color are made at the expense of some of the lubricating qualities, 

 the transparent but dark reddish oil being in reality the best 

 lubricator. 



7. It must not evaporate and leave the parts dry, as is the case 

 with kerosene, parafine oil, coal oil, and in general all distilled 

 oils, which being products of distillation, that is, condensed vapors, 

 will of course evaporate again, principally when the parts become 

 warm Ijy friction or otherwise. 



8. Not only can no good lubricator be the product of distilla- 

 tion, but the substance itself must never have been submitted to 

 a certain degree of heat, suflicient to cause a chemical change in its 

 constituents to take place ; when an oil has been boiled it is ruined 

 as a lubricator ; any boiled vegetable or animal oil is inferior ; so 

 is tar. And even if the oil was only heated to a temperature con- 

 siderably below its boiling point, the lubricating qualities are much 

 impaii'ed. 



9. It must not be too thin ; but thick, adhesive, and stick to 

 the parts, not being removed by mere friction, as is the case with 



