Muriatic Genus. 59 



genus predominates, if magnefia be, next to 

 the filiceous, the moft copious ingredient, and 

 the compound poflefles the characters of the 

 muriatic, and not thofe of the filiceous 

 genus. 



SPECIES I. 



Combined with the Serial Acid, and barely 

 mixed <with other Earths^ in an earthy* 

 or fe mi-indurated Form. 



Pure magnefia has no where yet been 

 found, nor even magnefia, barely combined 

 with fixed air, and free from all mixture of 

 other Earths. When combined with fixed 

 air by art, 100 patts of it contain at a medium 

 30 of aerial acid, 48 of mere Earth, and 22 

 of water ; but thefe proportions are variable 

 within certain limits, the fixed air being 

 found in the proportion of from 25 to 37, 

 the Earth from 40 to 48, and the water from 

 20 to 30. in general when the proportion of 

 fixed air is greateft, that of water is fmalleft, 

 and vice verfa. 



I. VARIETY. 

 Mixed with Siliceous Earth. 



Spuma Mans, Meerjhaum of the Germans. 

 Keffekill, 



This is found in various parts of the world, 

 particularly in the Eaft, in veins of moderate 



thicknefsj 



