292 Anahfis of the Scb'ieferfpath from Cornwall. 



Ammonia, a fmall quantity of reddifli brovyu precipitate. 



Oxalate of ammonia, a copious white precipitate. 



Sulphuric acid and fulphate of foda both produced plentiful 

 white precipitates ; the latter not immediately : the folution, 

 therefore, contained neither flrontia nor barvtes. 



Carbonate of potalh alfo occafioned a plentiful white pre- 

 cipitate : upon heating tlie folution after filtration no further 

 dcpofition took place, as would have done had the folution 

 •contained magnefia. 



The infoluble white refiduum was boiled in fulphurlc and 

 nitric acids, but neither of them dilfolved any part of it : 

 potalh diflblved it entirely : had it been alumina, its ftate of 

 extreme divifion would have admitted of its eafy folution in 

 acids: it therefore appears to be filica. The fame appearance 

 took place with folution of the fchieferfpath from Germany. 



From thefe preliminary experiments it appears that the 

 fchieferfpath is a carbonated lime intermixed with oxide of 

 iron and a very fmall quantity of filica; fo fmall, indeed, 

 that, had it not always appeared in every folution which was 

 made of the foreia;n as well as the Englifli, I fliould have 

 been induced to (ufpeft that its prefence was rather acci- 

 dental, than neceflarily entering into the compofition of the 

 mineral. 



Employing the method which has already been mentioned, 

 aoo grains loll by folution in nitric acid of 1*40 fpecific gra- 

 vity 86*8 grs. of carbonic acid, equal to 43*4 per cent. Now, 

 according to the analyfis juft given of carbonated lime, 44 

 parts of carbonic acid are united to 55-475 of lime : hence 

 43*4 <^f carbonic acid muft be combined with 54"7,i8 of 

 lime, forming together 98-118 of carbonated lime. 



The nitric folution was confiderably diluted with water, in 

 order to effeft more readily the fubfidcnce of the filica ; which 

 being carefully collected, after repeated wafhing, and dried in 

 a glals veflel by the heat of an Argand's lamp,\veighed -i of 

 a grain, equal to -05 per cent. 



The oxide of iron precipitated by ammonia was fubmitted 

 to a red neat, and treated with carbonaceous matter fo a^ to 

 render it magnetic : on weighing, it was found equal to -8 

 per cent. 100 parts confilfof 



Carbonate of lime - 98-118 

 Silica - - -05 



Oxide of iron - - '8 



Lofs 



98-968 

 1-032 



lOO'OOO 



XLV. Dc. 



