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LIX. Thermo -chemical Researches. 

 By M. Julius Thomsen*. 



Part I. — Berthollet's Theory of Affinity. 



IN his Essay on Chemical Statics, Berthollet laid it down as a 

 rule of the action of acids on salts, that a base when in presence 

 of two acids tends to divide itself between them in proportion to the 

 bulks of those acids and their respective affinities for that base. 

 But up to the present time no one has been able to submit this 

 theoretical law to a satisfactory experimental verification. M. 

 Thomsen thought to accomplish this by thermo-chemical re- 

 searches. For since different acids disengage different quantities 

 of heat in combining with the same base, the decomposition of 

 a salt by an acid must be accompanied by a thermic effect f, 

 which will be greater the more complete the decomposition, and 

 which ought to admit of measurement. 



The aim of the present memoir is the special study of the 

 reactions of nitric acid and hydrochloric acid on sulphate of 

 soda; but each of them requires a very great number of experi- 

 mental determinations. Thus, for the first we must know the 

 thermic effect produced in the following reactions : — 



1. Neutralization of sulphuric acid by soda. 



2. Neutralization of nitric acid by soda. 



3. Decomposition of sulphate of soda by nitric acid. 



4. Decomposition of nitrate of soda by sulphuric acid. 



5. Supersaturation of sulphate of soda by sulphuric acid. 



6. Supersaturation of nitrate of soda by nitric acid. 



7. Action of sulphuric acid on nitric acid. 



Reactions 3, 4, 5, and 6 must, moreover, be studied with 

 varying proportions of the substances concerned in the action. 



The author observes that, in order to derive any advantage 

 from these data, they must be known with great accuracy. He 

 thinks it is necessary that the approximation should be at least 

 to within \ per cent. ; and he believes that this was attained 

 in his determinations. He adds that he could use no previous 

 determinations, because they were far from approaching this de- 

 gree of precision. Thus the heats determined by Messrs. Favre 

 and Silbermann for the neutralization of nitric, hydrochloric, 

 hydrobromic, and hydriodic acids are from 10 to 12 per cent. 



* Translated from an abstract of an article in Poggendorffs Annalen 

 (vol. cxxxviii. p. 65), published by M. C. Marignac in the Bibliotheque Uni- 

 verselle de Geneve, December 1869, pp. 301-318. 



t [The author has coined a new word for this case, Warmetbnung , which 

 ought perhaps to be translated calorific tonality, but for which we think 

 the more simple expression, thermic effect, may be used, which can alike de- 

 note an absorption or a disengagement of heat. — C. M.] 



