XVr Memoir on BardigVione or Sulphate of Lime^ containing a Sketch 

 of a 1'heory of the true Nature of Plaster^ as well as of its Pro- 

 perties ; /// order to detennme the differences that exist between it 

 and Bardl^Uone. 



•i>- 



By The Count de Bournon^ F.R.S. Sic. 

 Fordgn Secretary of the Geological Sucietj/. 



[Translated from the original French Manuscrlp*,] 



1 HIS substance is a combination of lime and sulphuric acid, in the 

 proportion, according to Vauquelin, of 0,40 lime and 0,60 sulphuric 

 acid. It has obtained various names : being called Chaux Sulfatee 

 Anhydre by Haiiy, Chaux Sulfatine by Brongniart, Anhydrite and 

 Wlirfelspath by Werner, Muriacite by Poda and Klaproth, Pierre de 

 Vulpino by Fleuriau de Bellevue, and Marmo bardiglio di Bergamo by 

 the Italian statuaries. The name sulphate of lime has hitherto been 

 applied to gypsum ; but as it is now well known that the simple 

 combination of lime and sulphuric acid produces bardiglione, while 

 water is essential to the composition of the former, that expression 

 is inapplicable, and might be supplied by that of Hydro-sulphate of 

 lime. 



Essential specif c Characters, 



A. Ctjstallographical. 



Primitive Crystal. A rectangular tetrahedral prism with square 

 bases, which, from every indication, do not belong to the cube, but 



2 Y 2 



