818 PHOTOS ALTS 



9. PROTOSALTS OF IRON. 



Iron combines with two proportions of oxy- 

 gen, and both oxides are capable of combining 

 with acids, I shall in this section consider only 

 the salts which contain protoxide of iron for their 

 basis. 



i. Protosulphate of iron. This well known 

 salt, when pure, is transparent, and has a light 

 green colour ; and is crystallized in oblique 

 prisms, having a rhomb for their base. Its con- 

 stituents are 



1 atom sulphuric acid 5 

 1 atom protoxide of iron 4*5 

 7 atoms water . 7*875 



17-375 



2. Protonitrate of iron. I obtained this salt by 

 dissolving iron in dilute nitric acid till the acid 

 refused to take up any more of the metal. The 

 solution, which was at first brown and opaque, 

 became gradually transparent by the escape of 

 nitrous gas, and assumed a light green colour, 

 with a shade of yellow. It was concentrated 

 under the exhausted receiver of an air pump, 

 over sulphuric acid. A small quantity of per- 

 oxide of iron precipitated when the greatest part 

 of the liquid had evaporated, and pretty regular 

 crystals of protonitrate of iron were formed. 



