35 TRANSACTIONS OF THE 



alumina in the salts, derived from the earth, and that 

 they are formed by the union of sulphuric acid with an 

 oxide of iron. The working of the salts for commercial 

 purposes, we think can never be done to advantage. 

 The oxides of iron form with the sulphuric acid, a con- 

 siderable number of salts, but the object of our analysis 

 was not to determine the precise species to which the 

 salt under consideration belongs; we incline to the 

 opinion, however, that it is a sulphate of protoxide and 

 peroxide of iron. 



It is stated in most chemical works, that when the 

 sulphate of potash is mixed with the persulphate of 

 iron § (Fe + ss) crystals will be formed by spontaneous 

 evaporation, similar to common alum, the sulphate of 

 alumina being replaced by the persulphate of iron with 

 which it is isomorphous. We then obtained its com- 

 position by substituting Fe for Al, in the formula. Now 

 when we added the sulphate of potassa to the solution 

 of the salts washed from the earth, no precipitate oc- 

 curred until it was reduced very low by evaporation ; 

 then it consisted of a yellow ferruginous salt, tasting 

 like copperas (Fe+S")+6 aq.; the sweetish astringent 

 taste of alum was entirely wanting. This experiment 

 seems to indicate that our salt is not sesquisulphate. 



