LEAD- COPPER BISMUTH. 329 



somewhat varying chemical composition ; it is almost insoluble in 

 water, soluble in most acids. 



Experiment 42. Dissolve by the aid of heat about 1 gramme of metallic bis- 

 muth in a mixture of 2 c.c. of nitric acid and 1 c.c. of water. Evaporate the 

 clear solution to about one-half its volume, in order to remove excess of acid, 

 and pour this solution of normal bismuth nitrate into 100 c.c. of water. Col- 

 lect the precipitate of bismuthyl nitrate on a filter, wash and dry it. Prove 

 the presence of bismuth in the filtrate by tests mentioned below. 



Bismuth subcarbonate, Bismuth! subcarbonas (BiO) 2 CO 3 . 

 H 2 O (?) (Oxy carbonate of bismuth, Pearl-white). Made by adding 

 sodium carbonate to solution of bismuth nitrate, when the subcarbo- 

 nate is precipitated, some carbon dioxide escaping : 



2Bi(N0 3 ) s + 3Na 2 CO 3 + H 2 O = 6NaNO 3 -f 2CO 2 + (BiO) 2 CO 3 .H 2 O. 

 A white, or pale yellowish-white powder, resembling the subnitrate. 

 It readily loses water and carbon dioxide on heating, when the yellow 

 oxide, Bi 2 O 3 , is left. 



A mixture of bismuth subnitrate, sodium bicarbonate, and water is often 

 prescribed, but, as such a mixture gives off carbon dioxide, it is better to sub- 

 stitute the subcarbonate for the subnitrate. 



Tests for Bismuth. 



Use a solution made by dissolving bismuth subnitrate or subcar- 

 bonate in the least possible quantity of dilute nitric acid, with gentle 

 heat. Dilute cautiously with water, adding a few drops more of the 

 acid if there is any tendency to precipitation. 



1. Add to the solution hydrogen sulphide or ammonium sulphide : 

 a dark-brown (almost black) precipitate of bismuth sulphide, Bi 2 S 3 , 

 is produced (Plate III., 8) : 



2BiCl 3 + 3H 2 S = 6HC1 + Bi 2 S 3 . 



2. Add solution of ammonium or sodium hydroxide, or carbonate : 

 a white precipitate of bismuth hydroxide, Bi(OH) 3 , or of bismuthyl 

 carbonate is produced. (See explanation above.) 



3. Solution of potassium iodide precipitates brown bismuth iodide, 

 B5I 3 , soluble in excess of the reagent. 



4. Solution of potassium dichromate precipitates yellow bismuthyl 

 dichromate, (BiO) 2 Cr 2 O 7 . 



5. A small quantity of bismuth or of any bismuth compound, 

 mixed with equal quantities of sulphur and potassium iodide, and 



