REPORT ON CHEMISTRY. 
419 
The experiments of the French philosophers led them to be¬ 
lieve in the existence of a very simple relation between the speci¬ 
fic heats and the atomic weights of compound bodies ; but they 
had not led them to a definite expression for that relation. 
Neumann has shown that the relation is the same in compound 
as in simple bodies, and by experiments on many chemical com¬ 
pounds, both natural and artificial, has generalized the conclu¬ 
sion of Dulong and Petit, and rendered it probable that a given 
quantity of heat will elevate the same number of degrees a por¬ 
tion of every solid body represented by its atomic weight. This 
extension of the law, should it he confirmed, will enable us not 
only to correct the atomic weights of the simple bodies directly, 
but to test ther accuracy through the compounds they form 
with each other. 
We are not yet in a condition to apply this law with perfect 
confidence to gaseous bodies. The experiments of De la 
Roche and Berard on the specific heats of the gases, gave re¬ 
sults for the simple gases which were very nearly conformable 
with the law ; but in some of the compound gases the same co¬ 
incidence did not appear: the researches of Haycroft and of 
De la Rive and Marcet were still less conformable in the com¬ 
pound gases. Dulong pointed out a source of error which he 
considered as entirely invalidating the method of experimenting 
employed by De la Rive and Marcet, and as rendering it pro¬ 
bable that the older determinations of De la Roche and Berard 
were better deserving of confidence. More lately he has pub¬ 
lished a highly ingenious investigation of these specific heats, 
obtained indirectly from the unlike tones produced by the dif¬ 
ferent gases when caused to pass at the same temperature and 
under equal pressures through a small wind instrument 
They are as follows :— 
Specific Heats. 
Const.Vol. 
Const.Press. 
Atmospheric air. 
1- 
1* 
1 -421 
Oxygen . 
1- 
1- 
1*415 
Hydrogen . 
1- 
1* 
1-407 
Carbonic acid. 
1-249 
1-175 
1-339 
Carbonic oxide . 
1- 
1* 
1-428 
Nitrous oxide . 
1-227 
1*10 
1*343 
Olefiant gas . 
1*754 
1*531 
1-240 
* Aim. de Chirn. tom. xli. p. 313, 
2 D 2 
