36 Dr. W. C. Henry's Remarks on the 



for heat. Now it had long ago been suggested by Dr. Dalton 

 as the most probable view of the relations of elastic fluids to 

 heat, that " the quantity of heat belonging to the ultimate 

 particles of all elastic fluids must be the same under the same 

 pressure and temperature." Dulong and Petit have since 

 inferred from their experiments, that the specific heats of se- 

 veral simple bodies in the solid state, when multiplied by their 

 atomic weights, give a constant quantity as their product*. 

 This relation has more recently been shown by M. Neumann 

 to extend to several compound mineral substances f. Admit- 

 ting, then, the equality of the specific heats of the gases when 

 equal volumes are compared, and also that their ultimate 

 atoms possess the same amount of heat, M. Dumas' s con- 

 clusion, that equal volumes must contain the same number of 

 ultimate atoms, is perfectly legitimate. But one of the ele- 

 ments of his calculation is erroneous:}:. M. Dulong, in his ela- 

 borate memoir on specific heat§, has subsequently established 

 the impossibility of obtaining, by the experimental process of 

 Delarive and Marcet, even an approximative measure of the 

 specific heats of the different gases, and has shown that the 

 earlier results of Delaroche and Berard are still those most 

 deserving of confidence. His own experiments, founded on 

 the relations between the specific heats of gases and their 

 powers of propagating sound, concur with those of Berard in 

 indicating considerable differences in the specific heats of the 

 gases, whether equal weights or bulks are made the objects of 

 comparison. Substituting, then, these results for those of 

 Delarive, we obtain, by the process of reasoning adopted 

 by Dumas, the opposite conclusion,— that equal volumes of 

 the different gases compared, contain unequal numbers of 

 atoms || . 



* Ann. de Chimie et de Phys. torn. x. p. 405. 



t Poggendorff's Annalen t vol. xxiii. p. 32. 



X Traite de Chimie appl. aux Arts, torn. i. p. 41. 



§ Ann. de Chimie et de Phys. torn. xli. p. 113. 



|| This argument is not urged as possessing more than a negative force. 

 The specific heats of the gases are not yet determined with certainty; and 

 it is even doubtful whether, if obtained, they would faithfully represent 

 the absolute heats, — a supposition manifestly involved in the principle of 

 calculation, that the specific heats are equal to the absolute heat of one 

 atom multiplied by the number of atoms in a given volume. It cannot, 

 moreover, be denied, that the specific heats of hydrogen, oxygen and nitro- 

 gen, obtained by Delaroche, are so nearly the same in equal volumes, that, 

 allowing for probable errors, they may safely be regarded as identical. 

 Hence, upon the principle of Dulong and Petit, those three gases must 

 contain the same number of atoms, and the weight of the atom of oxy- 

 gen must be represented by 16 (the number adopted by Berzelius) instead 

 of 8. 



