3^4 Analyjis of the Sp'tntl. 



M. To feparate the fulphate of magnefia from the fulphate of alumine, I ftrongly ignited 

 the wh(Je in a porcelain crucible for half an hour ; after which I difFufed the faline mafs in 

 water, and filtered it. The alumine thus feparated, was diffolved in the fulphuric acid, and 

 cryftalliz^d in alum. 



N. The folution of pure fulphate of magnefia was precipitated hot by the carbonate of 

 potafli. The carbonate of magnefia wafhed and dried, weighed 20 L- grains ; but after ftrong 

 ignition, there remained only 8i grains of pure magnefia. 



O. The waters ufed in the wafliings (of which that afforded by the decompofition of the 

 fulphate of alumine F, had preferred its yellow colour), were all evaporated to drynefs. The 

 faiine mafs, difFufed in water, again let fall a little earth, which 1 added to the fmali quantity 

 of flocks remaining after the experiment G. This being urged by a red heat with cauflic 

 potafh, and treated with the fulphuric acid, was decompofed into filex and alumine. 



P. All the alum obtained in the experiments K, L, M, and O, which weighed 665 grains. 

 Was diffolved in water, and the boiling folution decompofed by carbonate of potafh. The 

 alumine wafhed with boiling water, and dried by a gentle heat, weighed 221 grains. But 

 after being purified by digeftton in acetous acid, and faturating this laft with ammoniac, it 

 tvas again well wafhed, and ftrongly ignited for a quarter of an hour. Its weight was then 

 Only 74y grains. 



QtThe filex of the experiments I, L, and O, colledted and ignited for half an hour, weighed 

 24I grains. Deducing the nine grains of increafe afforded by thdmortar A, there will re- 

 main 15} grains for the part afforded by the fpinel. 



This analyfis, therefore, gives for one hundred parts of the fpinel : 



Alumine (P) --.____ 74)50 



Silex (Q.) - - - - - 15,50 



Magnefia (F) - . . - - 8,25 



Oxide of iron ^[|) i;^^^ r,5o 



Calcareous earth (C) - » -- - 75 



100,50 



The increafe of half a grain, which is here found contrary to the rule, fince there muft 

 always neceffarily be fome lofs, can only arife from the drynefs of the ftone in its natural 

 ftate, which cannot be given to its feparate parts even by ftrong ignition. 



I muft here mention a phenomenon which occurred in another analyfis of the fpinel, which 

 guided me to the preceding, and of which the defcription may not be totally ufelefs. After 

 having treated the fpinel with potafh and the muriatic acid, the earth precipitated from the 

 muriate by ammoniac was thrown into a folution of cauftic potafh. The refidue was dif- 

 folved in the muriatic acid, and after having feparated a fmall portion of filex, the folutioo 

 was concentrated by evaporation. 



At 



