330 Mr. Chenevix*s Analysis of Corundum , and of 
I put it into the agate mortar, and ground it as fine as I could. 
The augmentation of weight was then noted ; and was always 
taken into account in the general result. I then put the whole 
into a platina crucible, with 200 grains of calcined sub-borate 
of soda, and exposed the mixture for an hour or two to a 
violent heat. When the crucible was cool, muriatic acid was 
boiled upon it and its contents ; and, in about twelve hours, all 
the glass disappeared. If I wished to obtain the silica directly, I 
evaporated the whole to dryness ; but, if otherwise, I precipi- 
tated by an alkaline carbonate, and washed the precipitate, in 
order to get rid of all the salts contained in the liquor. This 
latter mode I believe to be preferable. I then re-dissolved the 
precipitate in muriatic acid, and evaporated for silica. But, as 
corundum contains only a small portion of this earth, there was 
little or no appearance of jelly. When the silica was thus pre- 
cipitated by evaporation, I filtered the liquor, and boiled it with 
an excess of potash. By this operation, the alumina was preci- 
pitated, and then re-dissolved by the excess of potash, from 
which it was finally obtained by muriate of ammonia ; the iron 
which had remained undissolved by the potash, having of course 
been previously separated from the alumina. This earth, and 
the silica, after being washed and dried, were ignited, and thus 
the weight of both was obtained., 
I shall exemplify, in a single instance, this mode of treat- 
ment ; and then present the results obtained from the different 
kinds of corundum. For this purpose, I shall select the blue 
perfect corundum, or sapphire, as the stone which has been the 
most ably analyzed by Mr. Klaproth. From a view of both 
analyses, the efficacy of the fusion with borax will be evident; 
and the results of the several experiments may be compared. 
