154 



Tables 146-148. 

 TABLE 146. —Friction. 



The required force ^' necessary to just move an object along a horizontal plane =/A'^ where .V is the normal pressure 

 on the plane and / the " coefficient of friction." The angle of repose * (tan * = F/N) is the angle at which the 

 plane must be tilted before the object will move from its own weight. The following table of coefficients was com- 

 piled by Rankine from the results of General Morin and other authorities and is sufficient for ordinary purposes. 



* Quoted from a paper by Jenkin and Ewing, " Phil. Trans. R. S." vol. 167. In this paper it is shown that in 

 cases wliere " static friction " exceeds " kinetic friction " there is a gradual increase of the coefficieut of friction as the 

 speed is reduced towards zero. 



TABLE 147. — Lubricants. 



The best lubricants are 5n general the following: Low temperatures, light mineral lubricating 

 oils. Very great pressures, slow speeds, graphite, soapstone and other solid lubricants. Heavy 

 pressures, slow speeds, ditto and lard, tallow and other greases. Heavy pressures and high speeds, 

 sperm oil, castor oil, heavy mineral oils. Light pressures, high speeds, sperm, refined petroleum 

 olive, rape, cottonseed. Ordinary machinery, lard oil, tallow oil, heavy mineral oils and the 

 heavier vegetable oils. Steam cylinders, heavy mineral oils, lard, tallow. Watches and delicate 

 mechanisms, clarified sperm, neat's-foot, porpoise, olive and light mineral lubricating oils. 



TABLE 148. — Lntrlcants For Cutting Tools. 



Mixture = ^ crude petroleum, % lard oil. Oil =: sperm or lard. 

 Tables 147 and i48quoted from "Friction and Lost Work in Machinery and Mill Work," Thurston, Wiley and Sons. 

 Smithsonian Tables. 



