Heat evolved in Chemical Combination. 



179 



giving a mean of 597*9. But since real sulphuric acid evolves 

 in combining with water 510-1 units of heat, and since acid of 

 6HO+ S 3 would still evolve with water 38*9, the total 

 quantity of heat which would have been evolved by the mix- 

 ture of dry sulphuric acid with water of ammonia would be 

 510-1 - 38-9 + 597*9 = 1069-1. 



The second series of experiments was executed with pot- 

 ash, and gave the following results. M. Hess was obliged, 

 however, to modify the mode of working. In consequence 

 of potash combining with water in various proportions, and 

 evolving thereby different quantities of heat, it was necessary 

 to use the solution of potash so weak as not to be affected by 

 any further addition of water ; and the mass of materials be- 

 came then so large as to preclude the use of the calorimeter, 

 which had hitherto served so well. The method of mixtures 

 was therefore adopted. The vessel in which the mixture was 

 effected was nearly globular in form, and about a litre in 

 capacity ; it weighed 290 grammes, equivalent to fifty-five 

 grammes of water. The water was first introduced, and then 

 so much solution of potash as was necessary for neutralizing a 

 certain quantity of acid. The temperature of the liquid was 

 observed immediately on the addition of the potash, and the 

 rise of temperature on the addition of the acid. All these 

 fluids were measured, and when the temperature had fallen to 

 the standard, the specific gravity was taken which gave the 

 weight. The specific heat of the solution was found to be 

 0-943. 



Sulphuric acid 6 HO + SO a 



3HO + SO3 



2HO + SO3 



HO, S0 3 



By establishing the same comparison here as in the case of 

 ammonia, we find that 



gave 



445*4 units of heat. 



483-4 



527*1 



597-2 



giving a mean of 601*0. 



The experiments with soda were carried on in the calori- 

 meter, and gave with H O + S O a , 608*7 units of heat; and 

 with 6 HO + S0 3 , 447*4 units. But 447*4 + 155*6 = 

 603*0. 



N2 



