CHEMICAL AFFINITY. 



193 



between sulphuric acid and nitrate of potash is sup- 

 posed to be as follows. On mixing eight atoms of the 

 acid with the same number of atoms of the salt, the latter 

 immediately undergoes partial decomposition, its base being 

 equally shared between the two acids which are present in 

 equal quantities ; and a state of statical equilibrium is attained 

 in which the bodies in contact are : 



(a) Four atoms sulphate of potash. 

 Four atoms nitrate of potash. 

 Four atoms sulphuric acid. 

 Four atoms nitric acid. 



The nitrate of potash, it is supposed, is decomposed to the 

 extent stated, and no farther, however long the contact is pro- 

 tracted. But let the whole of the free nitric acid now be re- 

 moved by the application of heat to. the mixture, and a second 

 partition of the potash of the remaining nitrate of potash is the 

 consequence ; the free sulphuric acid decomposing the salt till 

 the proportion of the two acids uncombined in the mixture is 

 again equal, when a state of equilibrium is attained. The mix- 

 ture then consists of: 



(b) Six atoms sulphate of potash. 

 Two atoms nitrate of potash. 

 Two atoms sulphuric acid. 

 Two atoms nitric acid. 



On removing the free nitric acid as before, a third partition 

 of the potash of the remaining nitrate of potash, between the 

 two acids, on the same principle takes place, of which the 

 result is : 



(c) Seven atoms sulphate of potash. 

 One atom nitrate of potash, 

 One atom of sulphuric acid. 

 One atom nitric acid= 



The proportion of the two acids, free, being always the same. 

 The repeated application of heat, by removing the free nitric 

 acid, will cause the sulphuric to be again in excess, which 

 will necessitate a new partition of the potash of the remaining 

 nitrate of potash, till at last the entire separation of the nitric 

 acid will be effected, and the fixed product of the decomposi- 

 tion be : 



(d) Eight atoms sulphate of potash. 



