Intelligence and Miscellaneous Articles. 467 



atoms, (p the cohesion of the compound body C, W its volume ; the 

 atomic volume of the compound is moreover \p-\-\p'. 



The quantities of heat necessary for raising the temperature of the 

 atoms by one degree are respectively in the case of the three bodies: — 

 (R+PXV-fl) 

 TE 



9 (iy + P)(V-4/) 



TE 



TE 



Now, to heat the atoms in the combination C, the same quantity 

 of heat must be used as if they were free * ; the latter quantity is 

 then equal to the sum of the two former, and after reducing we have 

 the general relation 



(p + P)(W-^-^ ) = (R + P)(V-^) + (R' + P)(V'-^). • (1) 

 After an obvious reduction this general relation may be written 

 (p + P)W-p(+ + v|/ f )=(R + P)V-R^+(R' + P)V'-Ry. 



In the case of gases the cohesions or internal pressures are feeble 

 as compared with the external pressure ; the atomic volumes are also 

 very small as compared with the apparent volumes, and the products 

 Rxjj, R\J/, p(\p + \p') may usually be neglected ; and we have then, with 

 a sufficiently close approximation, 



If the volumes of two gases which combine are known, as well as 

 the volume of the compound in the state of gas or of vapour, we 

 obtain by means of this relation the cohesion of the compound as a 

 function of the cohesion of the elements and of the external pressure. 



This relation gives rise to some remarks. 



(1) When two gases combine in equal volumes without conden- 

 sation, 



V=V'=|W, 



^=i(R+R'), 



The cohesion of the compound is equal to the arithmetical mean of 

 the cohesions of the elements ; it is independent of the external 

 pressure. 



Thus the cohesion of binoxide of nitrogen is equal to half the sum 

 of the cohesions of nitrogen and of oxygen. These two permanent 

 gases have very feeble cohesions. The cohesion of binoxide of nitro- 

 gen should also be very small ; and this gas is permanent. 



In like manner the cohesion of hydrochloric acid is the arithme- 

 tical mean of the cohesions of chlorine and of hydrogen. Chlorine, 



* G. A. Hirn, Exposition Analytiqueet Experimentale, 1865. 



