On the Dcweijlite. 33 



solution thus produced, was evaporated to drj^icss, redissolvcd in 

 water, and the solution after Iiaving been rendered slightly acid by 

 the farther addition of muriadc acid, was thrown upon die filter to 

 separate the silica, whicli, after repeated washings and calcination, 



amounted to 20.4 grs- 



In order to learn whether alurainc was present, the muriatic solu- 

 tion, after a partial evaporation to reduce its bulk, was decomposed 

 by carbonate of potash at a boiling heat. The precipitate w^as thor- 

 oughly digested in a solution of potash, the alkaline hquor separated 

 from the residue by the fdter, and after a slight super-saturation with 

 muriatic acid, again treated with carbonate of potash. No precipitate 

 occurred. 



Having assured myself in this manner of the absence of aki- 

 mine, I dissolved the residue, upon which the potash had been diges- 

 ted, in dilute sulphuric acid. It w^as entirely soluble. 



Carbonate of potash added to the sulphuric solution, at a boiling 

 heat, threw down a copious precipitate, which after separation and 

 drying, was found to be a pure carbonate of magnesia. 



Having satisfied myself that the Deweyhte consisted of silica, mag- 

 nesia and water, I proceeded as follows. 



25 grains were calcined during one hour, in which time tliey lost 

 5 grains in weight. The calcined powder, fused with tliree times Its 

 weight of potash, and treated widi muriatic acid as before, afforded 

 10 grains of silica. 



The muriatic solution was decomposed by carbonate of potash, 

 and the precipitate after being dried and calcined for nearly an hour, 

 weighed 10 grains. Thus presenting us with the following resuh. 



Silica, 10. or per hundred 40 



Magnesia, 10. " " " 40 



Water, 5. " '' '' 20 



25. 100. 



It is therefore a compound of 

 5 atoms silica, 

 4 atoms magnesia, 

 4 atoms of water, 



10. 

 10. 

 4.5 



24.5 



