272 Mutual precipitations of metallic OXIde^* 



Sulphite of cop- Several colourr, are prepared with fulphate of copper, brft 



per may bs freed ([^g jp,,,-, which it always contains, and which hitherto has nevef 



tVomircnj i , r . . . « i xr i-n. 



been completely leparated, alters the (hade. Ir, to accomplilh 



this iaft object, the iron is ftrongly oxided by means of nitric 



acid, or, which is better, of oxigenated muriatic acid, the 



iulphate of iron may be intirely precipitated by pouring a 



fufficient quantity of potafti into it, and by heating and agitating 



the liquor. 



and fulphate of Green fulphate of iron is alfo frequently employed in the 



iron, from cop- ^^^ ^^^j j^^ many of them it is defirable that it (liould not 



per. . -' 



retain any copper. Iron has the property of feparating it, but it 



appears that it only does fo imperfeclly.and requires much time. 



It would doubtlefs be more advantageous to employ potafh) 



and to pour a little into the green fulphate : the precipitate of 



black oxide of iron would be fpeedily re-dilTolved by agitation, 



and would precipitate, at the fame time, the oxide of copper 



and the red oxide of iron, if there was any in the greerl 



fulphate. 



Ammonia dif- I Qiall here remark that, having employed ammonia to difco^i 



iron^at'a'mini- ^^'" ^'^^ copper in the green fulphate^ I obferved that, on adding 



mum. an excefs of alkali, the oxide of iron was diffolved in great 



abundance, though it is known thal^ in the fame circumftances, 



it does not di{r)lve the very oxided iron. The folution left irt 



the air is decompofed, the ammonia efcapes, and a black cruft 



is formed on the furface of the liquid which foon defends it from 



the confad of the air. In analyfes, ammonia is frequently em-» 



ployed to feparate iron, but this method is not good unlefs it 



had been ftrongly oxided before* This induces me to believe 



that this c-ircum fiance might have prevented Bergman from 



feparating iron from nickel by means of ammonia; for he found 



that his folution contained the oxides of both metals, and this 



could only have arifen from the iron not having been fufficiently 



oxided. 



Oxigenated mii- I alfo difcovered, by the fame means, that the oxide of' 



Tiate ; '"^''*;"''y oxigenated muriate of mercury precipitates the red oxide 



precipitates the _ o y i r 



red oxide of irotiof iron with the grealeft facility, and thofe of zinC and copper 



anathcfeolainci^yj^ their muriatic folution. 



and copper . ', /rij • rr-i ... 



Oxide ot filver Havmg dilTolved a piede or filver m nitric acid, I obtained 



precipitates ox- ^ jji^e liquor compofed of copper and filver. A little potafh 



poured into the folution formed a flocculent precipitatci com- 



|)ufed» 



