550 On the Influence of Pressure upon the Freezing of Fluids. 



of 10 atmospheres, does not increase Ath of a degree Cent, in 

 temperature; besides this, as the differences of c and h take 

 place both in the same sense, and hence in the difference 

 c— A are subtracted, we can set with a near approach to accu- 

 racy for c—h the difference of both specific heats simply. If 



the value of -j- estimated from (I.) be substituted in (III.)> 



dr 

 and if the sign of -j- be changed like that of r in the former case, 



we have — dr , . f /nx 



— =c-A-f— — . ...... (2) 



dt a-\-t ^ ' 



From this we must conclude, that when the freezing-point 



changes, the latent heat must also change; for water is c=l, 



and, according to Person*, /i=0'48. Hence we have — 



dr 



^=0-52 + 0-29 =0-81; 



at 



that is to say, when the freezing-point of water is lowered by 

 pressure, the latent heat decreases 0"81 for every degree. 



We must not confound this result with that already expressed 

 by Personf. From the circumstance that the specific heat of 

 ice is kss than that of water, the latter concluded with great 

 probability, that when the freezing-point, without increasing the 

 pressure, is simply lowered by preserving the fluid perfectly mo- 

 tionless, the latent heat must then be less than at 0°. This 

 decrease may be expressed by the equation — 

 dr , 



the above equation (2) therefore shows, that when the freezing- 

 point is lowered by pressure, the latent heat, besides the change 

 due to the last-mentioned cause, suffers a still further diminution 



expressed by the quantity ; this in the case of water is =0*29, 



and it is this which corresponds as equivalent to the exterior 

 work accomplished. 



The late obsei-vation of Person J, that ice does not melt com- 

 pletely at a definite temperature, but becomes softer immediately 

 before it reaches the melting-point, I have left unnoticed, as its 

 introduction would merely render the development more difficult, 

 without serving any important end ; for the decrease of latent 

 heat which corresponds, as equivalent, to the produced work, 

 must be independent of the little irregularities which may take 

 place dui-ing the melting. 



♦ Comptes Rendus, vol. xxx. p. 526. t Ibid vol. xxiii. p. 336. 



X Ibid. vol. xxx. p. 526. 



