338 Analysis of some Steatites. 



4.. The residuum, being lixiviated with* distilled water, 

 left a white powder, which, when calcined in a red heat, 

 weighed 64 parts. It was pure silex. 



5. Ammonia, mixed with the liquor separated from the 

 silex, formed in it a yellow precipitate of little bulk, from 

 which 1*5 of aluminc were separated by means of caustic 

 potash. The remainder was oxide of iron, weighing 3 parts 

 and a half. 



6. Having precipitated the iron and alumine by means of 

 ammonia, I put into the liquor a 'solution of carbonate of 

 soda, and set it to boil. As soon as the mixture began to 

 grow hot, it grew turbid and deposited a large quantity of a 

 white powder, which, when washed and calcined, weighed 

 £7 parts. This substance was magnesia, for with sulphuric 

 acid it formed a salt that had all the characteristics of com- 

 mon sulphate of magnesia. 



flexible laminar talc therefore is compounded of 



Silex 62 



Magnesia 27 



Oxide of iron 3*5 



Alumine 1*5 



Water 6 



100 



From the smallness of the quantity of the iron and alu- 

 mine, I think these substances maybe presumed not to 

 be essential to the formation of the stone ; so that perfectly 

 pure laminar talc may be deemed a compound of silex and 

 magnesia. 



Analysis of compact rose-coloured Talc. 

 In the analysis of this variety T pursued the same pro- 

 cesses as in that of the preceding; I therefore need not enter 

 into the particulars. The following are its results : 



Silex 64 



Magnesia 22 



Alumine 3 



Iron mixed with magnesia ... 5 



Water 6 



100 



Analysis 



