1823.] Sulphuric Acid, Peroxide of Iron, and Ammonia. 409- 



excess of acid was, perhaps, owing to the presence of the small 

 quantity of sulphate of alumina, for this salt contains more sul- 

 phuric acid than the triple salt, and no allowance was made in 

 the calculation for the excess. 



If, therefore, we neglect the alumina, the composition of the 

 salt in question will be 



Persulphate of iron 41*95 



Sulphate of ammonia 12*1 1 



Water 45-94 



i j 



100-00 

 I conceive that the salt which Mr. Cooper obtained by- 

 dissolving the oxide of iron precipitated from the pernitrale by 

 ammonia in sulphuric acid, is similar to that of which I have 

 now given the analysis. The quantities of sulphuric acid and 

 peroxide of iron are nearly in similar proportions ; the greater 

 quantity of water which he assigns may be accounted for by the 

 ammonia having been included with it. 



As the results deducible from this analysis seem to agree so 

 well with M. Mitscherlich's idea, that peroxide of iron and alumina 

 are isomorphous, and afford additional proof of the correctness 

 of his views, I was more particularly anxious to determine the 

 quantity of water, with as much accuracy as possible. For 

 although the crystals of alum belong to the formes lintites of 

 Haiiy, which may occur in crystals of very different substances; 

 yet if in two such compound salts there exists a close analogy 

 between their component parts and their form, it deserves atten- 

 tion ; and on this account I subjected alum formed of sulphate of 

 alumina, sulphate of ammonia, and water, to analysis. One 

 hundred parts of this ammoniacal alum were dissolved in water, 

 and decomposed by nitrate of barytes ; the sulphate obtained 

 weighed 104-46 = 35*90 of sulphuric acid ; a like quantity of 

 the same alum decomposed by ammonia gave 11-24 of alumina. 

 From the known composition of sulphate of alumina, it is evi- 

 dent that one-fourth of this sulphuric acid is not combined with 

 alumina, and it must, therefore, be united with the ammonia, 

 and on this supposition, the composition of ammoniacal alum 

 will be : 



Sulphuric acid 35-90 



Alumina 11-50 



Ammonia 3-86 



51-26 

 Water and loss 48*74 



100-00 



Making sulphuric acid the basis of the calculation, and on 

 •account of the great weight of the sulphate of barytes the errors 

 of experiment are diminished, we find that 24 atoms of water 



