LEAD COPPER BISMUTH. 187 



Poisonous properties and antidotes. Compounds of lead are directly 

 poisonous, and it happens, not infrequently, that water passing through leaden 

 pipes or collected in leaden tanks becomes contaminated with lead. Water 

 free from air and salts scarcely acts on lead ; but if it contain air, oxide of lead 

 is formed, which is either dissolved by the water or is decomposed by the 

 nitrates or chlorides present in the water, the soluble nitrate or chloride of lead 

 being formed. 



If the water contains carbonates and sulphates, however, these will form 

 insoluble compounds, producing a film or coating over the lead, preventing 

 further contact with the water. Rain water, in consequence of its containing 

 atmospheric constituents, and no sulphates, acts as a solvent on lead pipe; 

 spring and river waters generally do not. 



Water containing lead will show a dark color on passing hydrogen sulphide 

 through it ; if the quantity present be very small, the water should be evapo- 

 rated to -j^jy or even y^y of its original volume before applying the test. 



The constant handling of lead compounds is one of the causes of lead 

 poisoning (painters' colic). As an antidote, mangesium sulphate should be 

 used, which forms with lead an insoluble sulphate ; the purgative action of 

 magnesia is also useful. (In lead works workmen often drink water containing 

 a little sulphuric acid.) 



Analytical reactions. 

 (Lead acetate or lead nitrate, Pb(NO 3 ) 2 , may be used.) 



1. To a solution of lead salt add hydrogen sulphide or ammonium 

 sulphide : a black precipitate of lead sulphide is produced (Plate 



111,1): 



Pb(N0 3 ) 2 + H 2 S = 2HN0 3 + PbS. 



2. Add sulphuric acid or soluble sulphate : a white precipitate of 

 lead sulphate is formed : 



Pb(NO 3 ) 2 + Na,SO 4 = 2NaNO 3 -f- PbSO 4 . 



3. Add hydrochloric acid or a soluble chloride : a white precipitate 

 of lead chloride, PbCl 2 , is produced, which dissolves on heating or 

 on the addition of much water, as lead chloride is not entirely in- 

 soluble. For the same reason, the precipitate is not formed when 

 the solutions used are highly dilute. 



4. Other reagents which give precipitates with lead solutions are : 



Potassium chromate, producing yellow lead chromate (chrome yellow). 



(Plate II., 6.) 



Potassium iodide, producing yellow lead iodide. (Plate III., 6.) 

 Alkali carbonates, producing white basic lead carbonate. 

 Alkali phosphates, producing white lead phosphate 



Copper, Cu n = 63.2 (Cuprum). Found in nature sometimes in the 

 metallic state generally, however, combined with sulphur or oxygen. 



