ALUMINA. 315 



Mr. Phillips considers so unaccountable. I 

 need hardly observe that 



SULPHURIC ACID. ALUMINA. 



3 atoms disulphate contain 15 + 13-5 



1 atom trisulphate . 5 + 6'75 



Total . . . 20 + 20-25 



Now, this is equivalent to 



Sulphuric acid 40 

 Alumina 40-5 



the very theoretic proportions which Mr. 

 Phillips deduces from an erroneous atomic 

 weight of alumina. 



III. When alumina is precipitated from an 3. From 

 alkaline solution, collected on a filter, well washed, of alumina. 

 and allowed to dry spontaneously on the filter in 

 a dry warm room, a hydrate is obtained, com- 

 posed of equal weights of alumina and water. 

 This is an experiment which I have frequently 

 made in Edinburgh and in London, where I was 

 in the habit of working in a room elevated con- 

 siderably above the ground ; but in Glasgow, 

 where my laboratory is in a ground floor situated 

 in a clay soil, and consequently rather damp, I 

 have found it much more difficult to obtain cor- 

 rect results, at least during the summer of 1823, 

 which was uncommonly cold and wet, when I 

 was occupied with this investigation. I shall re- 

 late one experiment which I made with consi- 



