414 M. J. Thoinsen's Thermo -chemical Researches. 



sulphate of soda experiences a decomposition increasing with the 

 proportion of acid. Its complete conversion into chloride would 

 absorb 1949 thermal units. 



Decomposition of nitrate of soda by sulphuric acid. — This reac- 

 tion gives rise to a disengagement of heat which, for an equiva- 

 lent of nitrate of soda, rises to — 



Thermal units. 

 For 1 equivalent of sulphuric acid . . 288 

 2 equivalents of sulphuric acid . . 379 



Decomposition of chloride of sodium by sulphuric acid. — Analo- 

 gous results : — 



Thermal units. 

 For 1 equivalent of sulphuric acid . . 244 

 2 equivalents of sulphuric acid . . 336 



Discussion of the Results of these Experiments. 



It follows from the preceding experiments, that when nitric 

 acid or hydrochloric acid acts on sulphate of soda, they give rise 

 to an absorption of heat, whilst the reaction of sulphuric acid on 

 the nitrate or chloride disengages heat. 



It is evident that the thermic effect which accompanies these 

 reactions may be regarded as the measure of the chemical de- 

 composition ; and experiment confirms this notion. When an 

 equivalent of sulphuric acid acts on an equivalent of nitrate of 

 soda, the same product is obtained as when an equivalent of nitric 

 acid acts on an equivalent of sulphate, or as when an equivalent 

 of each of the two acids acts on an equivalent of soda simul- 

 taneously. 



Now it follows, from the thermochemical principles previously 

 explained by the author and admitted by all without dispute, 

 that the heat disengaged by the reaction of three bodies (A, B, 

 and A') is the same, whatever may be the order in which they 

 react : 



(A, B, A') = (A, B) + (AB, A') = (A', B) + (A' B, A) ; 

 from which it follows that 



(AB, A') - (A'B, A) = (A', B) - (A, B) ; 



which, in the present case, may be interpreted thus : the difference 

 between the thermic effects produced by the reaction of sulphuric 

 acid on nitrate of soda, and by that of nitric acid on the sulphate, is 

 equal to the difference of the heats disengaged in the neutralization 

 of soda by the two acids. 



In fact, experiment gave for these differences : — 



Thermal units. 

 15689 -13617 = 2072 



288- (-1752) =2040. 



