408 Mr. Graham on the Heat disengaged in Combinations. 



The rise of temperature on saturating a whole equivalent 

 of hydrate of potash with sulphuric acid will therefore be 

 ll°-38. 



The saturation of sulphate of water, already in combination 

 with sulphate of potash in the bisulphate of that base, is at- 

 tended with the disengagement of a still greater quantity of 

 heat. Half an equivalent of fused bisulphate of potash, dis- 

 solved in water like the acid of the former experiments, was 

 neutralized by potash, with the usual conditions : — 

 Before mixture . . 62°«74 62°-92 63°*05 

 After mixture . . . 68°'95 69°-12 69°-22 

 Rise 6°-21 6°-20 6°'17 Mean 6°'19. 



The saturation of the whole equivalent of sulphate of water 

 in a solution of the bisulphate of potash therefore occasions 

 the disengagement of 12°-38 ; free sulphate of water only 

 11 0, 38; the excess in the former case being l o, 00. 



Now, in saturating two equivalents of sulphuric acid, the 

 heat evolved is twice ll°-38, or 22°»76; but as 12°-38 is 

 evolved in saturating the second equivalent of sulphuric acid, 

 it follows that 10 o, 38 only are evolved in saturating the first 

 equivalent of acid. Hence we have — 



Heat disengaged in the formation of bisulphate of potash 10 o, 38 

 saturating acid of ... ... 12 0, 38 



22°-76 

 The cold, on dissolving an equivalent of crystallized sul- 

 phate of potash, 54>'55 grains, in 100 grammes of water, was 



Mean 2°-29. 



On mixing solutions of sulphate of potash and sulphate of 

 water (dilute sulphuric acid), to form bisulphate of potash, 

 cold is produced, as was formerly observed ; and from this 

 cause sulphate of potash, when dissolved in water acidulated 

 with sulphuric acid, produces more cold than in pure water, 

 by about one-third of the quantity from the latter. This ex- 

 cess of heat absorbed I was disposed to connect with the com- 

 bination of sulphate of water with sulphate of potash, and for- 

 mation of a double salt. But it is remarkable that the mag- 

 nesian sulphates, which we do not certainly know to combine 

 with hydrated acids, as sulphate of potash does, likewise pro- 

 duce greater cold on dissolving in acidulated than in pure 

 water. 



Thus an equivalent of crystallized sulphate of magnesia, 



