Refearches on Alumine, 3 1 



VI. I precipitated by liquid ammonia a folution of pure 

 alumine, and obtained, after tbe precipitate had been dried, 

 a quantity of fpongy alumiue, equal in weight to that which 

 I had obtained from the fame quantity of a folution of alu- 

 mine when I decompofed it by carbonat of ammonia, and 

 when I did not add an excefs of precipitant. A hundred 

 parts of potafhed fulphat of alumine, entirely decompofed by 

 ammonia or the carbonat of ammonia, fumifhed 21 parts of 

 fpongy alumine dried in a temperature of between 72 and 85 

 degrees of Fahrenheit's thermometer. Thefe 21 parts were 

 reduced to 9, by deficcation, in a violent fufingheat. A'hun- 

 dred parts of the alum which I employed, contained, then, 

 no more than about nine parts of pure dried alumine : a pro- 

 portion very different from that which fome authors have 

 afcribed to the compofition of this fait. 



VII. I diilblved alumine to faturation in nitric acid diluted 

 with water, and placed in this folution a rhomboidal cryftal 

 of carbonat of lime. A flow erTervefcence was produced, 

 which even continued for fcveral weeks. The alumine depo- 

 rted by this operation produced no erTervefcence with acids. 

 On this occafion it appeared to be doubtful whether calcareous 

 earth alone be a medium proper for uniting alumine with 

 carbonic acid ; and, if I thought there was reafon to afcribe 

 to this caufe the great quantity of carbonic acid which I 

 found in the dolomies, it was becaufe I w r as deceived by the 

 extraordinary quantity of alumine contained in fome fpeci- 

 mens which I analyfed. Mr. Tennant had more reafon to 

 afcribe the properties of the dolomies to the triple combina- 

 tion of the carbonic acid with the calcareous earth and the 

 macrncfia, which the dolomies always contain in a large 

 quantity, while the purevt contain only an infinitely fmall 

 quantity of alumine. It appears that the dolomie is to the 

 bitter-Jpatb of the Germans what marble is to calcareous fpar. 



I fubjecled to diltillation alumine precipitated from its ful- 

 phat by carbonat of ammonia, and dried at the temperature 

 of the atmofphere. I obtained from this operation, after a 

 long and flrong incandefcence, only w r ater 5 but no carbonic 

 acid gas. 



VIII. I thought I fhould be able to explain the experiment 

 of Fourcroy, which proves the pure and limple combination 

 of alumine with carbonic acid, becaufe it is not difengaged 

 with eflervefcence during the decomposition of aluminous fo- 

 lutions by alkaline carbonats, by afcribing its refult, in part, 

 to the triple and concrete formation of an aluminous com- 

 bination of carbonic acid and alkali; but I abandoned that 

 opinion by obferving that, when a folution of alumine is de- 

 compofed 



