Analysis of adhesive Slate. 135 



It contains therefore 27 per cent, of carbonic acid. 

 The' analysis was conducted in the following manner : 



1. One part of the mineral in fine powder was put inlo 

 four parts of concentrated sulphuric acid, in which it dis- 

 solved with evident effervescence j and the solution was 

 evaporated to drvness. 



2. The residuum was diffused in water, and a gelatinous 

 matter separated, which was still a little yellowish. This 

 was silex. 



3. The liquor was filtered, 



4. The gelatinous residuum was washed with boiling water, 

 till no further trace of sulphuric acid was discoverable. 



5. This water and the filtered liquor were evaporated to- 

 gether, till there remained but ten drachms. 



6. Some sulphate of lime separated, which was decom-t 

 posed by an alkaline carbonate; and after it had been heated 

 and roasted 0*08 of pure lime were obtained. 



7. The liquor separated from the sulphate of lime being 

 concentrated by heat, yielded crystals of sulphate of iron 

 and of sulphate of magnesia. 



8. T put the whole, without separating the crystals, into a 

 platina crucible, and exposed the saline mass to a strong 

 heat for two hours. ^ 



9. After cooling, the mass had an ochrey colour, and a 

 bitter taste. On it I affused boiling water, filtered and 

 washed the residuum. 



10. The oxide of iron remained on the filter. After hav- 

 ing been dried and roasted it weighed 0*09. 



11. I added to the liquor carbonate of ammonia, when a 

 white earth was precipitated, which, dried and roasted, ap- 

 peared to be magnesia, and weighed 0.28. 



12. The yellowish gelatinous residuum (No. 4) was di- 

 gested in muriatic acid, till its colour became entirely white. 



13. Being filtered and washed, the liquor was of the co- 

 lour of pale white wine. Being precipitated with ammonia. 

 I obtained some more oxide of iron, which, washed and 

 roasted, weighed 0*03. 



}4. Having redissolved this oxide of iron, and that of 

 No. 10, there yet remained 0*008 of silex. 



I 4 15. The 



