Intelligence and Miscellaneous Articles. 77 



dilates with displacement of the point of application of an external 

 pressure ; this proportion, which is insensible in the case of hydrogen, 

 is perfectly appreciable with air, and much greater in the case of 

 carbonic acid. 



M. Hirn has assumed the internal work to be negligible in hy- 

 drogen. He has deduced from the preceding equation the absolute 

 specific heat of that gas ; and by applying the law of Dulong and 

 Petit to the absolute specific heats, he has been able to obtain under 

 this hypothesis the values of y with respect to various gases. By 

 combining the equation (1) with the law of absolute specific heats, 

 we may compare the values of y for various gases without the as- 

 sumption of any hypothesis with regard to hydrogen. 



Air and Hydrogen. — According to the experiments of M. Reg- 

 nault, we have, for hydrogen, C = 3*409 between zero and 200°, 

 a = 0-003661 between zero and 180°, and £ = 0-06926. The equa- 

 tion (1) gives for this gas 



K=2-41523-y (2) 



The experiments of M. Regnault give for air, C' = 0*23 751 be- 

 tween zero and 200°, ct' = 0'00367 between zero and 100°. The 

 equation (1) applied to this gas gives 



K' = 0-168512-y (3) 



Now 100 parts by weight of air contain 77 parts of nitrogen and 

 23 parts of oxygen ; if we apply, with M. Clausius, the law of abso- 

 lute specific heats to air considered as a compound body, designating 

 by Kj and K 2 the absolute specific heats of nitrogen and oxygen, 

 100K' = 77K 1 + 23K 2 . 



But if we apply the same law to nitrogen, to oxygen, and to hy- 

 drogen, the atomic weights of which are to each other as the num- 

 bers 14, 16, and 1, 



K=14K 1? K=16K 2 . 



By transferring these values of K 1 and K 2 into the preceding 

 equation, 



K'=0'069375K; 

 and by replacing K and K' in this last equation by the values de- 

 duced from the equations (2) and (3), we have, finally, 

 y' = O-O69375y + O'0O0956. 



Carbonic Acid and Hydrogen. — The data furnished by M. P*eg- 

 nault's experiments for carbonic acid are, C" = 0'21692 between 10° 

 and 210°, a" = 0-003710 between zero and 100°, <T =0-52901. The 

 equation (1) gives for this gas 



K" = 0-171302-y" (4) 



If we represent by \ the atomic weight of hydrogen, the mean 

 atomic weight of carbonic acid is ^-, and according to the law of 

 absolute specific heats, 



Replacing K and K" in this equation by the values deduced from 

 the equations (2) and (4), we have 



7 "=0-068181y + 0-006628. 



