by Rock-crushing and its Consequences, 9 



formed heat of friction produced by internal movements taking 

 place in such materials after crushing has occurred, must be the 

 source of a large amount of heat over and above that originally 

 due to the crushing itself. Thus, for example, if we assume a 

 surface of such disintegrated material sliding over a similar sur- 

 face, or over a rough surface of coherent rock, and under the 

 pressure of ten miles of rock of the specific gravity of granite, at 

 the rate of one foot per second, and if we take the coefficient 

 of friction as low as 0*5, we have 4,326,600 foot-pounds of fric- 

 tional work per second, which, divided by J ( = 772), gives 5604 

 units of heat evolved per second from each square foot of sur- 

 face ; and to this development there is no limit while the circum- 

 stances continue the same, except that of the distance that one 

 surface is forced over the other. And great as is this evolu- 

 tion of heat under such enormous pressures, it would be further 

 increased in the event of the fragmentary particles being heated 

 so as to present incipient viscosity of surface and more or less 

 of mutual agglutination. 



Temperature with respect to any given solid material is depen- 

 dent upon the units of heat present in a unit of mass or of 

 volume of the substance. If for the same total heat we dimi- 

 nish the mass or volume, the temperature is proportionately 

 increased. When the material is surrounded by matter capable 

 of carrying off heat by conduction, or evection, or radiation, and 

 the heat is evolved within the mass by work done upon it, then 

 another condition, that of time, has to be taken into account ; 

 for the shorter the time within which a given amount of heat 

 due to transformation of work is evolved within the unit of mass, 

 the less of that total is dissipated by conduction &c. 



A familiar example of this is every day seen in the light and heat 

 elicited by abrasive friction, or collision between hard bodies. 

 When two lumps of granite or other hard stone are struektogether, 

 heat and light are instantly evolved at the small surface of con- 

 tact, where the material of one or both masses is crushed. The 

 work done may be but that of the crushing of a fraction of a 

 grain of the stone ; but it is great in reference to the extremely 

 brief instant of time during which the work is performed; the 

 crushed particles are raised to a temperature of luminosity for a 

 brief moment because there is not time for the surrounding sur- 

 faces of the cold stone to carry off the heat evolved by conduc- 

 tion, though the dissipation of heat thus produced is such that 

 the luminosity again instantly disappears. The temperature at 

 the crushing-point is greater as the work done in a unit of time 

 and upon a given weight of the material is greater. That the 

 temperature capable of being thus produced approaches that of 

 the fusing-point of steel, is evident from the phenomenon of a 



