210 °* A VARIETY OF THE CORUNDUM* 



A. 



Analyfis, pulvc- 100 grains of this ftone, which had been reduced to a powder 

 tion 'trituration. ,n a ** ce ' mortar, were not afte&ed in the flighted degree by 

 the magnet. 



The powder was of a lilac inclining to a pink-colour. Ex- 



pofed to a ftrong red heat for half an hour, it loft |-| of a 



grain in weight. Its colour was unaltered. — It was now 



rubbed (in a dry ftate) to a finer powder in a mortar of flint. 



Upon weighing it again, I found that it had gained no accef- 



fion,to its weight from the abrafion of it. 



Boiled to dry- It w r as now pat into a filver-crucible, and covered with a 



then wafted- ' ^ omt » on of potafli in * alkohol, mixed with an equal bulk of 



and the refidue diftilled water, and the orucible was placed in a fand-bath, 



w^ J hed treate nd and and the fluid S ra(iLmll y evaporated: and at laiVit was boiled 

 again, & c . till to drynefs. The fait which remained at the bottom of the 

 little remained, crucible, was dilTolved in diftilled water, and its folution poured 

 off from a fpungy earth, and a portion of the undecompofed 

 ftone which had fubfided. This operation was repeated in 

 the fame way with frefti portions of potafli, until the whole of 

 the ftone was decompofed, except a fmall quantity of a fpungy 

 earth, which was thrown upon a nitre and waflied with dif- 

 tilled water, until what pafled through it ceafed to caufe the 

 leaft turbidnefs in a folution of nitrat of mercury. The edulco- 

 rating water was added to the tblution which had been effected 

 by potafli. 



B. 



The undecom- The powder which remained on the filtre was dried. It 

 pofed refidue was wa5 of a greyifli white colour. I put it into a fmall matrafs 

 b"fuiphuric Cd and rnoiflened it with diftilled water, and then dropped fome 

 acid. 



* I have reafon to fubferibe to the opinion of Mr. Chenevix, 



which he has given us in the mafterly and fcientific paper on the 

 arfeniats of copper, with which he has enriched the annals of mine- 

 ralogy and chemical analyfis, that it is by the means of alkohol alone, 

 that potafli can be prepared, which is fit for delicate experiments. 

 I was induced to employ a folution of potafli in alkohol, becaul'e it 

 has been faid, that during the procefs for obtaining it in a dry ftate, 

 it a<5te in fome degree upon the iilver vefTels, in which its folution is 

 evaporated. By evaporating it in contatt <vjitb the fpar, I thought 

 that this would be lei's likely to happen. 



rectified 



