Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/367

XV. Memoir on Bardiglione or Sulphate of Lime, containing a Sketch of a Theory of the true Nature of Plaster, as well as of its Properties; in order to determine the differences that exist between it and Bardiglione.

By the Count de Bournon, F.R.S. &c.
Foreign Secretary of the Geological Society.

───────

[Translated from the original French Manuscript.]

This 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 Sulfatée Anhydre by Haüy, Chaux Sulfatine by Brongniart, Anhydrite and Würfelsath 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 specific Characters.

A. Crystallographical.

Primitive Crystal. A rectangular tetrahedral prism with square bases, which, from every indication, do not belong to the cube, but