164 Elements of Mineralogy. 



water is abfolutely taftelefs and precipitates no 



metallic folution. 



The powdered ftone, thus edulcorated, is 

 to be dried by heating it to rednefs, and then 

 weighed, and 100 grains taken for fubfequent 

 experiments : it were better if ftill more were 

 ufed, but the analyfis would be more expen- 

 five. 



The powder is next to be digefted in 8 or 

 10 times its weight of aqua regia y in a boil- 

 ing heat in a retort to which a receiver is luted, 

 and the digeftion reiterated as long as any 

 thing appears to be diffolved by frefh portions 

 of the acid. I found mica to require 50 

 times its weight of aqua regla before it was 

 entirely decompofed, as the acid is fo volatile 

 as very foon to diftill over. Oil of vitriol 

 has the advantage of bearing a greater heat, 

 diflblving barofelenite, and of ading more 

 powerfully on argill than aqua regla ; but a 

 large retort muft be ufed, for, often towards 

 the end it puffs and throws up the Earth or 

 ftone, and carries it into the receiver ; and it 

 does not fufficiently act on calces of iron, if 

 thefe be much dephlogifticated. Spirit of 

 nitre affedu them ftill lefs : hence I often uie 

 oil of vitriol firft, then precipitate by a mild 

 alkali what it has diffolved, and rediflblve the 

 precipitate in aqua regia. A perfect folu- 

 tion 



