THE ACCOMPANYING SUBSTANCES. 



II 



formed. This precipitate had all the properties of alumina ; The potato left 

 and, when well warned and ignited, weighed 92 grains. Con-^j^J^^ 

 fequently, deducting 5 from the filica, for the abrafion of the fuffered the alu- 

 mortar, we (hall have for refult, mina t0 m ' 



Silica 

 Alumina 

 Iron 

 Lofs 



5,25 

 92 

 1 

 1,75 



Waflied and ig- 

 nited it weighed 

 9Z grs. 



Comp. parts de» 

 duced. 



100,00. 



The chief difference between thefe proportions and thofe As Klaproth 

 effablifhed by Mr. Klaproth, is in the filica. That chemift Jjjjj^ j£j a 

 did not find any notable portion of it in the fpecimens he exa-this point was' 

 mined. This naturally induced me to make a very ftri£t re- P a . rtlcu,ar1 / exa * 

 fearch into every poffible means by which any filica might have 

 been introduced into the refults ; whether by the borax, the 

 alkali, or any of the other re-agents I had ufed. But, finding 

 very clearly, that none of thefe fubftances did contain any, I 

 could no longer hefitate to believe, that the proportion I have 

 here ftated, was actually contained in the fapphire I analyzed. 

 I am likewife convinced, that no more than the quantity I 

 have mentioned was worn from the agate mortar and peftle ; 

 for my conftant practice was, to weigh them, both before and 

 after I had ufed them, in fcales which, when charged with four 

 pounds on each end, turn eafily with the tenth part of a grain. 



The general refults, from all the different kinds of corundum, 

 were as follows : 



Blue perf eft Corundum, or 

 Sapphire. 

 Silica - 5,25 



Alumina - - - 92 

 Iron 1 



Lofs - - - J, 75 



100,00. 



Imperftcl; Corundum from the 



Carnatic. 

 Silica - 5 



Alumina - - - 91 

 Iron - - - 1,5 



Lofs - - - - 2,5 



100,0. 



Red perfeel Corundum, or Component parti 



Silica 

 Alumina 

 Iron 

 Lofs - 



Ruby. 



7 

 90 

 1,2 

 1,8 



of diff. kinds of 

 corundum* 



100,0. 

 hnperfeel 



