76 SCHWEINFURT GREEN 1 . 



solution is then mixed with a large quantity of water, 

 when the bismuth is precipitated as basic chloride. 



50. BISMUTH AND COPPER. 



By carbonate of ammonia bismuth is precipitated, 

 while copper remains in solution, but the separation is 

 only approximate. It is more accurate to precipitate 

 the bismuth as basic chloride, as in No. 49. 



51. SCHWEINFURT GREEN. 

 CuO, A + 3(CuO, As0 3 ). 



When this substance is heated with caustic potassa 

 the acids are extracted, and red suboxide of copper 

 left, one-third of the arsenious acid being converted 

 into arsenic acid. 



If the filtered liquid be neutralized with nitric acid, 

 and nitrate of silver gradually added, a red brown pre- 

 cipitate of arseniate of silver is first produced, and 

 afterwards a yellow precipitate of arsenite of silver. 



In order to separate the two acids, the solution, pre- 

 viously acidified with nitric acid, is mixed with excess 

 of ammonia, and sulphate of magnesia added, which 

 has been mixed with so much chloride of ammonium 

 that it is no longer precipitated by ammonia. The 

 arsenic acid is thus precipitated by arseniate of mag- 

 nesia-ammonia. After the lapse of twelve hours, the 

 precipitate is collected upon a dried and weighed fil- 

 ter, washed with dilute ammonia, and thoroughly dried, 

 at 100. It then has the composition 2 MgO, NH 4 O, 

 AsO 5 -fHO, and contains 60.53 per cent, of arsenic 

 acid. It is not safe to ignite this precipitate, since 

 arsenic is then liable to be reduced and volatilized. 



