75 



The mixture of sulphide of bismuth and sulphide of 

 lead is detached, as far as possible, from the filter, the 

 latter incinerated, and the ash added to the precipitate 

 which is then oxidized in a capacious capsule, with con- 

 centrated nitric acid, a little sulphuric acid added lest 

 there should not be sufficient, and the excess of nitric 

 acid expelled by heat. The mass is then treated with 

 a little water, the solution of sulphate of bismuth fil- 

 tered off from the sulphate of lead, the latter washed 

 with water containing sulphuric acid, dried, and ignited. 



From the filtrate the teroxide of bismuth is precipi- 

 tated by carbonate of ammonia in excess ; the liquid 

 is digested for some time to insure the complete sepa- 

 ration of the precipitate, which is then filtered off, 

 washed, detached as far as possible from the filter, and 

 ignited in a porcelain crucible, when it is converted 

 into yellow teroxide of bismuth. The filter is incine- 

 rated separately. 



If the oxide is fused with cyanide of potassium, it is 

 reduced and determined as metallic bismuth. 



The best method to separate bismuth from the other 

 metals depends upon this, that by the addition of a 

 large quantity of water to the hydrochloric acid solu- 

 tion, there is obtained a perfectly insoluble precipitate 

 of basic chloride of bismuth (2 Bi 2 3 +Bi 2 C1 3 ), that 

 may be weighed in this state, or reduced to a metallic 

 state, by fusing with cyanide of potassium. In order 

 to separate the lead, the concentrated solution is mixed 

 with so much hydrochloric acid that the chloride of 

 lead is precipitated, and the addition of a few drops of 

 water causes no turbidity. Dilute sulphuric acid is 

 then added, allowed to stand for some time, stirring 

 occasionally, then mixed with alcohol, well stirred, and 

 the sulphate of lead left to settle down. It is then fil- 

 tered, washed with alcohol containing hydrochloric 

 acid, and afterwards with pure alcohol. The filtered 



