164 ARRANGEMENT OF THE ELEMENTS IN COMPOUNDS. 



formulae which exhibit the composition of the neutral sulphates 

 of a metal in four different states of oxidation, an atom of 

 metal being represented by M. 



Formulae of neutral sulphates. 

 i. ii. 



As consisting of As consisting of metal 



oxide and acid. and salt-radical. 



MO + SO 3 . M + SO 4 . as in sulphate of soda. 



M 2 O + SO 3 . M 2 + SO 4 . as in sulphate of suboxide of 



mercury. 

 MO 2 + 2SO 3 . M+2SO 4 . as in sulphate of peroxide of 



tin. 

 M 2 O 3 + 3SO 3 . M 2 + 3SO 4 . as in sulphate of peroxide of 



iron. 



The acid is seen in the first column to be always in the proper 

 proportion to form a sulphatoxide of the metal in the second 

 column ; and these sulphatoxides correspond exactly with 

 known chlorides, such as M Cl, M 2 Cl, M C1 2 , M 2 C1 3 . 



Thirdly : It offers a more simple and philosophical explana- 

 tion of the action of certain metals upon acid solutions, and of 

 the decomposition of such solutions in other circumstances. 

 Thus when zinc is introduced into hydrochloric acid, it is 

 allowed on both views, that the metal simply displaces the 

 hydrogen which is evolved, and that chloride of zinc is formed 

 in the place of chloride of hydrogen. In the same way when 

 zinc is introduced into diluted sulphuric acid, which contains 

 the sulphatoxide of hydrogen on the binary theory, hydrogen 

 is simply displaced and evolved as before, and the sulphatoxide 

 of zinc formed instead of the sulphatoxide of hydrogen. The 

 metal in question appears to be incapable of decomposing pure 

 water by displacing its hydrogen at the temperature of the air ; 

 but this fact does not interfere with the preceding explanation, as 

 zinc may have a greater affinity for sulphatoxygen than for 

 oxygen, and, therefore, be capable of decomposing the sulphat- 

 oxide, but not the oxide of hydrogen. If the acid solution, 

 however, contains sulphate of water, as it does on the old 

 view, then zinc does and does not decompose water, decom- 

 posing it when in combination, but not when free. It then 

 becomes necessary to assume that the presence of the acid en- 

 hances the affinity of the metal for the oxygen of the water, 

 in a manner which cannot be clearly explained ; for the solu- 



