320 On the Colouring Principle of Lapis Lazuli. 



as might have been expefted, looking only for iron ; but \l 

 "was proper thus to exclude the other metallic fubftances, 

 which are precipitated by this re-agent. 



4. With the hydro-fulphure of ammonia there was a 

 beautiful green precipitate. 



5. With ammonia, a white precipitate. 



6. With pot-afli, a light blue precipitate.-^The two laft 

 paflTcd to yellow in drying. 



Comparative experiments were made at the fame time 

 with a folution of the nitrat of iron, and the refults were 

 totally different. 



G. That no doubt might be left refpeSing the nature of 

 the fubftances, the prefence of which might have had an in- 

 fluence in thefe refults, fynthefis was called in to the aid of 

 analyfis. Sulphure of iron was prepared in a direft manner; 

 the nitric acid was poured over it in fufficieut quantity, and 

 the liquor, when filtered, was diluted with abundance of 

 water, that the exccfs of the acid might no longer precipi- 

 tate the fulphurated hydrogen which was poured over it. In 

 this ftate the fame re-agents which had been before employed 

 prefenied all the fame phenomena. One might have fup- 

 pofed that the fulphat of iron, (not oxydated,) in the fame 

 circumftances, would have given fome analogous effects ; 

 but the pruffiat of pot-afh produced only a white precipitate, 

 as profeffbr Prouft had announced. 



H. It was eafy, after this, to conclude the analyfis of the 

 red fulphat of lime of Montolier : it confirmed what I had 

 announced, that it depended only on the oxyd of iron; and, 

 bcfides, determined with accuracy the quantities of the con- 

 ftituent parts as follows : 



Sulphuric acid - - - - - ap'i 



Lime -- - - - - -16 'O 



Oxyd of iron - - - - - 21 '9 



Silex .----.. 8-6 



Water carried off by the firft calcination - 22*3 

 Lofs .,_-_-- 2'i 



lOO'O 



But 



