IODINE. 95 



with the sulphuric acid to form a neutral salt — the sul- 

 phate of soda. This is a very good example of com- 

 bination and decomposition. In consequence of the 

 powerful affinity which sulphuric acid has for soda, 

 both the salt and water are decomposed; and the 

 chlorine and hydrogen being free from their combi- 

 nations, unite together to form muriatic acid (216). 



191. Chlorine is procured from muriatic acid by 

 the action of some substance capable of abstracting 

 its hydrogen; the most convenient for this purpose 

 are those which contain much oxygen. The usual 

 process is to heat together a mixture of muriatic acid 

 and oxide of manganese, a substance which is rich in 

 oxygen; the oxygen which is thus given off, takes the 

 hydrogen of the muriatic acid, with which it forms 

 water, and sets free the chlorine. 



192. Another and yet cheaper process is to heat a 

 mixture of common salt, oxide of manganese, and sul- 

 phuric acid ; in this case the sulphuric acid decom- 

 poses the salt, and the muriatic acid formed, is decom- 

 posed as fast as it is set free, by the oxygen of the 

 oxide of manganese. 



193. Iodine, bromine, and fluorine, are substances 

 hitherto undecomposed, and therefore called elements, 

 which in many respects resemble chlorine ; like it, 

 they form acids by combining with hydrogen, and 

 unite to the metals to form a numerous series of com- 

 pounds resembling chlorides, which are called iodides, 

 bromides, and fluorides. None of these substances are 

 of much importance ; those most deserving of notice 

 are the iodide of sodium, which exists with the chlo- 



