on the specific heats of Metals. 269 



weights generally received in this country ; and yet Mr Potter 

 has the advantage of all the researches made by chemists during 

 the thirteen years which have elapsed since the French memoir 

 was published. There is not indeed the slightest ground for 

 asserting that the numbers in column second are " completely 

 arbitrary, referring neither to the opinions of chemists nor to 

 the results of analyses?'' 



Nor is this all. Mr Potter professes to compare the numbers 

 of Berzelius with those of Dulong and Petit, in a table given 

 in page 82 ; but finding them in the book he has consulted 

 adapted to the oxygen scale, he multiplies them by seven to 

 bring them to the hydrogen scale (!!) thus obtaining and setting 

 down a list of numbers which no one ever dreamt of as repre- 

 senting the atomic weights of these bodies. Though Dalton 

 adopts the ratio of 7 : 1 as expressive of the relation of the atomic 

 weight of oxygen to that of hydrogen, he ought to have known 

 that Berzelius, whose numbers he thus multiplies, does not, and 

 this would have prevented him from falling into such an error. 

 Let me request his attention to the following extract from Dr 

 Thomson's History of Chemistry, vol. ii. page 297. " He 

 (Dalton in the 3d volume of his System, published in 1827,) 

 still adheres to the ratio 1 : 7 as the correct difference between 

 the weights of the atoms of hydrogen and oxygen. This shows 

 very clearly that he has not attended to the new facts which 

 have been brought forward on the subject. No person who has 

 attended to the experiments made on the specific gravity of these 

 two gases during the last twelve years, could admit that these 

 specific gravities are to each other as 1 : 14. If 1 : 16 be not 

 the exact ratio, it will surely be admitted on all hands, that it 

 is infinitely near it. 11 — " Dr lire," says Mr Potter, " adopts 

 7.5 as an atom of oxygen." In which of the ancient authors 

 docs Mr Potter find this? 



Rut in the paragraph already quoted from Mr Potter's paper, 

 while he denies that they have proved the law of equal specific 

 heats, he says the law " holds I find with singular fidelity in 

 common temperatures, excepting in one very remarkable case, 

 that of silver!" Now let us take the atomic weights of Dr 

 Thomson, and multiplying them separately into the specific 



