2j4 Curfory Vtetu of fame of the 



earths already known, and which may be contained in mi- 

 neral fubftances, can be difcovered : 



ift, Sili'x. It di'Tolves in the cauftic alkalies, efpecially 

 by the help of heat, from which it is precipitated by acids j 

 an excefs of which redilToJves it. The folution of this earth 

 in acids forms itfelf into a jelly bv evaporation, and when 

 it has been dried it becomes iufoluble in thefe menftrua: 

 this furniflies an excellent method for feparating it from other 

 earths. In this (late It is white, granulated, dry to the touch, 

 and perfeftly infoluble, 



2d, Alurnine. It diflblves alfo in fixed alkalies and acids, 

 from which it does not feparate itfelf, as filex does, by evapo- 

 ration. It retains the water with force, and its parts become 

 agglutinated and are brought into clofer union by heat. In 

 this ftate it is white, femi-tranfparent, and adherent to the 

 tongue. The combination of alumine with the fulphuric 

 acid gives, by the addition of a few drops of the fulphat of 

 potafh, oftaedral crv'ftals of alum. 



3d, Zirconia. It is not attacked by the cauftic alkalies ; 

 acids, however, diflblve it when it is very much divided, but 

 not when it has been ftrpngly calcined ; with the fulphuric 

 acid it forms ah infoluble fait ; it adheres weakly to all the 

 other acids, which it abandons at a very moderate degree of 

 heat : in a word, when very much divided, it diflblves in the 

 alkaline carbonats, when completely Saturated with carbonic 

 acid. When it is pure, and ftill contains water, it has a 

 light draw colour, is femi-tranfparent, and has a vitreous 

 frafture like gum arable; bat when it has been calcined in 

 a crucible, it is white, opake, rough to the touch, and dif- 

 fjlves only with difficulty in acids. 



4th, Glucine. This earth diflblves, as alumine does, in 

 acids and alkalios ; but it diflcjlves alfo in carbonat of am- 

 monia, and furniflies no alum with the fulphuric acid or 

 with potafli. The falts which it forms with the acids are 

 highly faccharine: when dry, it has a beautiful white co- 

 lour, is exceedingly light, and foft to the touch, and has no 

 favour. Its parts are not agglutinated by heat as thofe of 

 alumine are. 



3t'b 



