Mr Potter on the Specific Heats of Metal. 81 



ed, and had anticipations that similar laws would be found for 

 liquids and solids generally. 



It has since been maintained, on the ground of experiment, 

 by the above-named French philosophers, that the law is only 

 applicable, in the first instance, to the atoms of simple bo- 

 dies, and requiring some modifications for those of compound 

 ones which they had not been able to ascertain. The nature 

 of caloric and its connexion with ponderable matter are still 

 the subjects of so much uncertainty and dispute, that much 

 more information will be necessary before we can arrive at 

 even a tolerable view of its general properties, and the laws 

 which they obey. But that Mr Dalton's proposition has a 

 basis in nature there can be no reasonable doubt, though, even 

 with MM. Dulong and Petit's modification and limitation, 

 there is still ground for suspecting that we are not yet within 

 sight of the general law. And to this effect Mr Dalton has a 

 remark in the appendix to the 1st part of the 2d volume of 

 the new system of chemical philosophy. 



However, the law as enunciated by the French philosophers, 

 " that the atoms of all simple bodies have the same capacity 

 for heat,'"' when applied to the class of the metals, holds, I 

 find, with singular fidelity in common* temperatures, ex- 

 cepting in one very remarkable case, namely, that of silver. 

 Whilst the exception remains, the law cannot be said to be es- 

 tablished, much less can MM. Dulong and Petit in the least 

 be said to have proved their proposition, as they have taken for 

 the atomic weights numbers completely arbitrary, without re- 

 ferring either to the opinions of chemists or the results of 

 analyses. Whence they obtained their numbers I shall now 

 show. They appear to have appropriated such portions of Ber- 

 zelius's numbers as suited their experiments. Thus, for bismuth 

 they have taken | of his number, for lead £, for gold $, for 

 tin |, for silver A, for zinc £, for tellurium \, for copper \, 

 for nickel \, for iron \, and for cobalt I, of his number. 

 Where a theory of definite proportions only is referred to, 

 such a proceeding might be warranted, but not so, on any 

 ground, when atoms arc considered without direct reference 

 to analyses; and not having done this, they can only be said 



NEW SERIES, vol.. v. NO I. .Til I. V 1831. P 



