On Berthelot's Thermo- Chemistry. 367 



ledge in this respect, one may be almost led to surmise that 

 the progress made in the present day in obtaining an insight 

 into the hidden nature of physical causes has not kept pace 

 with this increased knowledge of facts ; and this would hint 

 again at the evil attendant on the want of a method. Also the 

 lull of any great discoveries in the field of pure physics during 

 the last few years would seem to make the direction of atten- 

 tion to any fresh pathway all the more opportune. 

 London, April 1880. 



XLVII. On Berthelot's Thermo- Chemistry. 

 By J. P. Cooke, Jun* 



THE new work of M. Bert helot, entitled Essai de Mdcanique 

 Chimigue fondee sur la Thermo-chimiej' presents for the 

 first time in a systematic form the results accumulated during 

 the past ten years from one of the most fruitful fields of inves- 

 tigation ever opened to the chemist. The book supplies a 

 most important want ; for the details of the work, published 

 in numerous separate papers rapidly following each other in 

 the chemical journals, have been almost unintelligible, except 

 to those who have followed the investigation from the begin- 

 ning, and no connected statement of the general principles 

 involved was accessible to the student. The work in this new 

 field has been done almost wholly by two investigators — Ber- 

 theiot, of Paris, and Thomsen, of Copenhagen. Guided by 

 different theoretical views, these skilful experimenters have 

 gone over very nearly the same ground ; and their united tes- 

 timony, concurrent as it is in most cases, gives a certainty to 

 the results obtained which is as fortunate as it is unusual when 

 the field explored is so extensive as the one we are considering. 

 These two men alone could write authoritatively on the sub- 

 ject ; and it is, perhaps, fortunate that the first presentation 

 should come from M. Berthelot, who has the usual skill of his 

 nation in exposition and generalization. 



In his introduction, Berthelot enunciates the fundamental 

 principles of thermo- chemistry under the three following 

 heads : — 



Principle of Molecular Work. 



I. The quantity of heat evolved is the measure of the sum 

 of the chemical and physical work accomplished in any reac- 

 tion. 



Principle of Conservation of Energy. 



II. When a system of bodies, simple or compound, starting 

 from a given condition undergoes either physical or chemical 



* From Silliman's American Journal, April 1880. 



