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Seition Stb. 



Alum. 



The combinations of argill with vitriolic acid are fo direrfi- 

 fied, as Mr. Vauquelin has lately Ihewn in a feries of curious 

 and interefting experiments, that to afcertain the limits of each 

 would require a particular examination which the generality of 

 the prefent inquiry does not at prefent permit to enter into. 



The refult of my former eflay was, that loo parts alum con- 

 tain 31,34. of earth dried at 465°; 17,06 of real vitriolic acid, 

 and 5 1 of water ; but the acid contained in vitriolated tartarin, 

 of which alum may contain 6 or 7 per cent, is not noticed ; but 

 being counted the whole amounts to 20 per cent. 



The earth heated to wbiiene/s may be reduced to 18, or ftiU 

 fewer parts. Wenzel and others fay 11,7, and I believe this to 

 be moft exadl. 



Hence 100 grains burnt alum, that is alum from which its 

 water was expelled, fhould contain 35,4 of real acid. But the 

 alums of different countries differ much. See Vauquelin in An. 

 Chy. & Pref to i Laborant. VII. 



Stilion 



