264 PRINCIPLES OF THE MECHANICAL THEORY OF » HEAT. 



constant xyressiire, may be denoted by r. This quantity of heat r is usually 

 called latent heat ; for it disappears as regards the thermometer, and during the 

 whole process the temperature t remains unaltered. 



The whole quantity of heat which, under the suppositions premised, must bo 

 supplied to the water at 0°, in order to convert it into steam at t° and of the 

 corresponding elasticity p, is therefore Q=W+r. But according to Reg- 

 nault's investigations the quantity of heat requisite for the object in question is 

 Q=606.5 + 0.305^; consequently, since r=Q—W, 



r=606.5 — 0.695^— 0.00002^2_o.oo00003^l 

 Instead of this value of r, Clausius makes use of the approximate value 



r=607-0.708^ . .1) 



according to which the numerical values of the sixth vertical series of the sub- 

 joined table are calculated, while the fifth column contains the corresponding 

 values for Q. 



If the whole quantity of heat were exclusively expended in external work, it 

 would be easy to determine, by the first law, the volume of the steam formed ; 

 for we should have r=Kpu^ and since r, A, and J9 are known, we might deter- 

 mine from this equation the volume ii of the space K K', (Fig. 10,) which is free 

 in the cylinder under the piston, while one kilogram of water at t° is converted 

 into steam at f. But the matter here is not so simple. 



