1823.] Native Sulphate of Iron and Alumina. 447 



circumstance renders it probable that the salt in question is not 

 producible artificially ; but this I have not tried. Crystals of 

 common sulphate of iron are sometimes mixed with it. When 

 the usual tests of the presence of iron are added to the solution, 

 the common evidence of the existence of that metal is obtained ; 

 prussiate of potash gives a very light blue precipitate, showing 

 that the iron is principally in the state of protoxide. 



One hundred grains of this double salt, cleared as much as 

 possible from the small fragments of slate-clay, were dissolved 

 in distilled water; the solution was filtered, and four grains of 

 earthy matter remaining undissolved, the deficiency was sup- 

 plied by an equal quantity of the pure salt. The solution was 

 heated with a little nitric acid to convert the iron into peroxide, 

 and nitrate of barytes was added to it as long as precipitation 

 ensued ; the sulphate of barytes washed and dried amounted to 

 91*25 grains, which are equivalent to 309 of sulphuric acid. 

 The slight excess of nitrate of barytes being removed from the 

 solution by means of sulphuric acid, the solution was decom- 

 posed by ammonia added in excess, and the peroxide of iron 

 and the alumina were of course precipitated together. 



The ammoniacal solution was examined in order to discover 

 whether any minute portion of lime or magnesia was contained 

 in the salt, but none was detected ; the precipitate was boiled 

 with a solution of soda to separate and dissolve the alumina, and 

 the peroxide of iron left being washed, dried, and ignited, 

 weighed 23 grains ; but the iron exists in the state of protoxide ; 

 and as 40 of peroxide consist of 36 protoxide and 4 oxygen, 23 

 are equivalent to 207 of protoxide, which is of course the quan- 

 tity contained in 100 grains of this double salt. 



The alkaline solution which contained the alumina was super- 

 saturated with muriatic acid, and the alumina precipitated by 

 carbonate of soda. When washed and ignited, it weighed 5"2 

 grains. 



I made an attempt to ascertain the quantity of water of crys- 

 tallization by direct means, but it failed ; indeed the nature of 

 the salt is such as to render it scarcely practicable ; for it is, I 

 think, more than questionable, whether anhydrous sulphate of 

 iron or of alumina can exist ; and, at any rate, there is great 

 danger either of not expelling the whole of the water by heat, or 

 of driving off some of the acid with it. 



From the experiments above stated, it appears that this salt 

 consists of 



Sulphuric acid 309 



Protoxide of iron 207 



Alumina 5*2 



Leaving for water 43*2 



100-0 



