OF ALUMINA. 315 



by digesting a mixture of acetic acid and hy- 

 drate of alumina till the acid was saturated. 

 No heat must be applied, because it occasions a 

 precipitation of a portion of the alumina from 

 the solution, which, however, again dissolves 

 when the liquid cools. A portion of solution of 

 acetate of alumina, thus formed, was left in a 

 covered Wedgewood evaporating dish for six 

 weeks during the summer of 1824. The whole 

 liquid evaporated away, and left the acetate of 

 alumina crystallized in long transparent four- 

 sided prisms, which were so firmly attached to 

 the dish, that they could not be removed with- 

 out destroying their shape. This is the only 

 simple salt of alumina which I have yet suc- 

 ceeded in obtaining in regular crystals. 



The portion of this salt which I subjected 

 to analysis was not in crystals, but in the state 

 of a powder obtained by exposure to a very 

 gentle heat. 9*625 grains of it kept for some 

 time in a red heat, left 2*25 grains of alumina. 

 Hence the constituents of the salt are 



1 atom acetic acid 6*25 

 1 atom alumina 2-25 



1 atom water 1*125 



The salt has a sweet and astringent taste, with 

 something of the flavour of acetic acid, dissolves 



