I*RETENDED NATIVE MAGNESIA. ^^5 



of dxigen on the oil, and the state of the oil, are absolutely 

 the same in the fabrication of plasters and of soaps ; T con- 

 ceive, that plasters Ought to be considered with respect to 

 soaps the same as insoluble metallic salts are to alkaline salts. 



I satisfied myself, that the want of consistency in soaps Soaps with 

 made with potash is not at all owing to the state of the oil, ^rom t*hena- 

 but to the nature of the compound; for by treating with tureof theal- 

 potash the oil obtained from a very hard soap of soda, I ^^^'* 

 could form nothing but a soft soap* 



XII. 



Account of a pretended pure native Magnesia*. 



HE German dealers in minerals sell under the name of Fossil sold as 

 pure indurated magnesia,, and as coming from Moravia, a ^"theGerinan 

 mineral substance found in amorphous masses of the size of dealers. 

 the fist, covered with an earthy crust of a yellowish white 

 colour, that slightly adheres to the tongue, and is a little 

 gteasy to the touch. Its fracture is dull, entirely compact. Its characters. 

 imperfectly conchoidal, and approaching to a plane : its co- 

 lour is yellowish white: it has small cavities, lined with lit* 

 tie mamillary projections, that appear to be composed of 

 crystalline points when viewed in a strong light: it is suffi* 

 ciently hard to scratch glass, and steel leaves a coloured 

 mark on it, but it does not strike fire with steel : its specific 

 gravity is 2*83: at its edges it is very transparent: it does 

 not absorb water, or adhere to the tongue. 



Before the blowpipe it cracks, and does not melt : it is not 

 at all phosphorescent: it dissolves with effervescence in the 

 nitric and muriatic acids; with the sulphuric it occasions a 

 copious precipitate* 



It cannot be confounded with the native magnesia of Difference of 

 Werner, which is easily scratched by steel, strongly adheres native magnet 

 to the tongue, and is of the specific gravity of 2 '88. ^^^' 



This mineral, analysed by Mr. Bucholz, yielded in 100 j. ^onent 



* Journal des Mines, January, 1807, p. 7o. 



parts 



