some of the Substances which accompany it, &c. 32 9 
uncertainty in the results. Even when very finely powdered 
corundum was exposed, with sixTmes its weight of potash, in 
a platina crucible, to a heat of 140° of Wedgwood, for two hours 
together, it was not acted upon in such a manner as to be fit 
for analysis. From all these experiments I concluded, that some 
more efficacious mode of rendering corundum soluble in acids 
was to be sought. 
I boiled a great quantity of sulphuric acid upon very finely 
powdered corundum, in a platina crucible. But, although the 
acid, after a great length of time, had dissolved a little of the 
stone, I did not find this method more satisfactory than the others. 
Nitric, muriatic, and nitro-muriatic acids, were less effectual than 
the sulphuric. Phosphoric acid, held in fusion with corundum, 
did not dissolve any notable portion of that stone, or render it 
soluble in other acids. 
I then had recourse to sub-borate of soda, (borax,) which I 
found to answer beyond my expectation. Two parts of that salt, 
calcined, and one of corundum, enter into fusion, at a tem- 
perature which 1 judged to be about 8o° of Wedgwood;* and 
a glass, more or less coloured, is formed. This glass is soluble- 
in muriatic acid ; and, by this method, it is easy to obtain a. 
complete solution of corundum. My general method of ope- 
rating was as follows. 
I took one hundred grains of corundum ; and, having several 
times made it red hot, and plunged it into cold water, I put it 
into the steel mortar, and treated it as already mentioned. I. 
then poured some very dilute muriatic acid upon it, to wash off 
whatever iron might have adhered, in consequence of its me- 
chanical action upon the mortar. After it was dried and weighed, 
# I have no doubt that a lower temperature would be sufficient. 
