12 On the Temperature attainable by Rock-crushing. 



creased by the amount required to overcome such initial pressure, 

 as has been already pointed out. 



Another and further source of heat arises after crushing and 

 detrusion of the fragmentary matter, and after the latter has 

 arrived at a temperature at which the fragments have become 

 more or less viscous and adherent by reason of the further work 

 expended in the deformation and detrusion by forcing forward 

 through highly irregular or constricted rock-channels of the 

 heated and now viscous mass. There do not exist at present 

 sufficient data by which to calculate the amount of work neces- 

 sary to a given amount of deformation in viscous masses ; and 

 hence we cannot calculate the amount of heat that in nature 

 might arise from it. Him, however, has shown that in the case 

 of plastic bodies such as lead the heat developed is proportionate 

 to the work done in deformation ; so that, if we knew the pressure 

 per unit of surface necessary to produce a certain deformation 

 in an already heated mass of given viscosity, we could calculate 

 how much its temperature would be exalted by the work of the 

 assigned deformation. 



Examples, however, are not wanting which prove that a very 

 large exaltation of temperature can thus be produced — as, for 

 example, in the old-fashioned method by which blacksmiths were 

 accustomed to light their fires. A thin square rod of very good 

 tough iron was hammered at its extremity by a succession of 

 rapidly given blows from a light hand-hammer. After a minute 

 or so the rod, for the portion of its length hammered at the extre- 

 mity ; became red, and in a second or two more of distortion of 

 its form by continuance of the hammering, the iron could be 

 made nearly white hot. 



A similar example, on a much larger scale, occurs in the pro- 

 cess of rolling iron or steel. When a heavy billet of iron or 

 steel, heated to a brilliant yellow heat, is passed between the 

 rolls of the iron mill, and the massive lump is rapidly elongated 

 into a bar, its temperature, notwithstanding that it is rapidly 

 and constantly losing heat by radiation and evection, is observed 

 visibly to increase, so that the mass becomes at a certain stage 

 white or welding hot by the transformation into heat of the 

 work of deformation so rapidly and powerfully applied to it. 



The action of the machine employed in the arsenal at Wool- 

 wich for making lead rods to be afterwards pressed into bullets 

 affords another striking example. In this machine a cylindric 

 block of lead, maintained at a temperature of 400° Fahr., is by a 

 steady pressure upon the end, which is 8""5 in diameter, of 16,700 

 lbs. per square inch of its surface, forced through an aperture at 

 the other extremity into a rod of0"*525 diameter, at such a rate 

 that five inches in length of the cylindric block becomes a rod 



