4 Abstract of Prof. Hess's Thermometrical Researches. 



The diiFerence here evidently results (says M. Hess) from 

 there having been more water in combination before the mix- 

 ture than after it. Thermoneutrality is therefore perfect only 

 when the circumstances of the salts before and after mixture 

 are the same. 



M. Hess remarks, that since all bases appear to evolve the 

 same quantity of heat when combining with any given acid, 

 we cannot assume the amount of heat evolved as a measure 

 of affinity. He points out that the numbers obtained in his 

 results are not really those indicating the heat evolved with 

 the acid, but only the difference between the heat lost by se- 

 paration from water, and gained by combination with the acid. 

 This difference is with the same acid a constant quantity. 

 It remains to know whether the quantities of heat evolved by 

 different bases in combining with water is the same, and from 

 experiments on the slaking of lime, and on the solution of hy- 

 drate of potash (K O. H O) in water, M. Hess deduces that 

 it is not, but that, the stronger a base is the more heat it 

 evolves in combining 'with 'water, the numbers with dry lime 

 and hydrate of potash being 163 and 323. 



Constitution of the Sulphates. — In relation to the nature of 

 acid salts, M. Hess makes the following observations. Ad- 

 verting to the views of the composition of common bisulphate 

 of potash, which by Bei'zelius is looked upon as a double salt 

 (KO.SO3 + HO.S O3), and by Graham as sulphate of 

 water, in which the second atom of (saline) water is replaced 

 by sulphate of potash, HO. S O3 (K O . S O3) corresponding 

 to HO. SO3 (HO), he considers the evidence obtained from 

 his experiments as disproving both views, on the following 

 grounds. 



If K O . S O3 ,when added to H O . S O3 (HO), did nothing 

 more than replace (H O), no heat could be developed, but it 

 is found by experiment that a considerable quantity is really 

 evolved*. This heat cannot be attributed to the displaced 

 water combining with the salt, for if water be directly added 

 to (K O . S O3 + H O . S O3), no heat whatever is evolved. 

 The true formula of the common bisulphate of potash he con- 

 siders to be represented by (K O + 2 S Og) + H O, from these 

 facts. When the dry bisulphate of potash (K O + 2 S O3) 

 is placed in the calorimeter; with a vessel of water of ammonia, 

 and the mixture effected, it is found that the quantity of heat 

 evolved is the same (-iOe units) as the second atom of acid 

 should have given when neutralized by an alkali after com- 



• Dr. Andrews, however, considers that no heat is evolved in the forma- 

 tion of such double salts. 



