Eiiumel-nt'wti of Alums, — NiW I/iJlrtir»e>tf. gjj 



different dntes of the combination of alumine with the fulphuric acid united at the fame 

 time with other bafes, that we muft diftinguifh feven dates in this combination, and that it 

 is neceffary to exprefs them according to the rules of the methodical nomenclature. Here 

 follow the fcries, the nature, and the names of thefe feven fulphates of alumine. 



1. Sulphate of aluminir, or the artificial combination of fulphuric icid and alumine. 

 This fait is aftringent ; it cryflallizes in laminx or flexible leaves, foluble in water. It has 

 never been defcrlbed nor named by chemifts. 



2. Acid fulphate of alumine. It is the foregoing fa't, with excefs of acid, from which it 

 differs by reddening blue vegetable colours. It is eafdy made by diflblving that fait in the 

 fulphuric acid, but it is not eafy to convert this into the neutral fulphate of alumine but by 

 boiling it a long time with its earth. This fait, like the firft, has not been defcribed. 



3. Saturated fulphate of alumine and of pot-a(h. It is the alum of the chemifts faturated 

 with its earth. I have defcribed the manner of making it. It is pulverulent, infipid, info- 

 luble, not cryftallizable, and is eafily converted into true alum by the addition of fulphuric 

 acid. 



4. The acid fulphate of alumine and of pot-afh. It is eafy to prepr.re it chemically. It 

 greatly refembies common alum ; but I have found none but that of La Tolfa which is of 

 the fa.ne nature. 



5. The acid fulphate of alumine and of ammoniac. It is eafily made in our laboratories. 

 I have not yet found it pure in commerce. It has all the properties of alum, and may be 

 ufed for the fame purpofes. 



d. The acid fulphate of alumine, pot-adi, and ammoniac. It is remarkable enough, that 

 this fhould be the nature of the alum mod frequently made in the arts, and that to exprefs 

 its coipbination fo many words diould be necellary. This, however, may be avoided by 

 refer\'ing the name of alum to this fubftance, which will be fulBcient to didinguifli k 

 perfeftly. 



7. The acidulous fulphate of alumine and of pot-afli. I am lefs acquainted with this 

 than the preceding fpecies. The name which I propofe to charafterife it has been fug- 

 gcfted to me, becaufe by adding a fmall quantity of pot-afli to the folution more than is 

 neceffary to obtain ottahedral crydals, it raanifedly pafles to the cubic form. 



8. Ladly, the phyfician, the chemift, and the manufacturer, with whom the ufesof alum 

 are greatly multiplied, will hereafter poflefs a knowledge of tlie fubftance they employ, and 

 may appreciate its eflccfls on the animal economy, and other bodies to which it is fo fre- 

 quently applied. 



VII. 



Dtfcriptkn of an Infrtiment proper to meafure the Volume of a Body •without phnigiiig it in am 



Liquid, By H. Sat, Capitaine dii Genie *'. 



X HE ordinary method of determining the fpecific gravity of folids by immerfion in a 

 liquid is inconvenient for powders and fluids, and impradicable witlj regard to fuch bodies 



' Abftrafi of a Memoir jiriiitcd in the Annalct de Chimic, XXIII. 1. 



