OF IRON. 327 



One salt, the carbonate, is anhydrous. 



Two, the protoxalate and prototartrate, contain 2 atoms 



water. 

 Three, the phosphate, diprotarseniate, and acetate, contain 



3 atoms water. 

 Two, the sulphate and nitrate, contain 7 atoms water. 



It has been already observed, that the chro- 

 mate of iron does not exist. 



10. PERSALTS OF IRON. 



Few of these salts being capable of crystalliz- 

 ing, they have not hitherto been subjected to a 

 rigid examination ; most of them, as far as my 

 experience goes, are sesquisalts, agreeing with 

 Gay-Lussac's law, that the quantity of acid 

 necessary to saturate an oxide increases with its 

 oxygen ; but to this rule there occur many ex- 

 ceptions. 



1. Persesquisulphate of iron. When a portion 

 of protosulphate of iron is peroxidized by means 

 of nitric acid, and cautiously concentrated till 

 the whole nitric acid is dissipated, we obtain a 

 red coloured mass, which dissolves only partially 

 in water. The solution has a red colour with a 

 tint of yellow the taste is astringent and very 

 harsh. When evaporated to dry ness it speedily 

 absorbs moisture, and deliquesces into a liquid 



ilcohol dissolves it readily. It strongly red- 



x t 



