LEAD. 165 



precipitation of lead- nitrate with sodium carbonate, but is 

 manufactured on a large scale directly from lead, by exposing it 

 to the simultaneous action of air, carbon dioxide, and vapors of 

 acetic acid. The latter combines with the lead, forming a basic 

 acetate which is converted into the carbonate (almost as soon as 

 produced) by the carbon dioxide present. 



The action of acetic acid on lead or lead oxide will be con- 

 sidered in connection with acetic acid. 



Carbonate of lead is a heavy, white, insoluble, tasteless pow- 

 der; the white-lead of commerce is frequently found adulterated 

 with barium sulphate. 



Lead iodide, Plumbi iodidum, PbI 2 459.7 (Iodide of lead}. 

 Made by adding solution of potassium iodide to lead nitrate : 



Pb2NO 3 + 2KI = 2KN0 3 + PbI 2 . 



It is a heavy, bright citron-yellow, almost insoluble powder, 

 which may be distinguished from lead chromate by its solubility 

 in ammonium chloride solution on boiling. 



Poisonous properties and antidotes. Compounds of lead are di- 

 rectly poisonous, and it happens, not unfrequently, that water 

 passing through leaden pipes or collected in leaden tanks be- 

 comes contaminated with lead. Water, free from air and salts, 

 scarcely acts on lead ; but if the water contains air, oxide of lead 

 is formed, which is either dissolved by the water or is decom- 

 posed 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 coat- 

 ing over the lead, preventing further contact with the water. 



Water containing lead will show a dark color on passing 

 hydrosulphuric acid through it; if the quantity present be very 

 small, the water should be evaporated to T V or even -5-^ of its 

 original volume before applying the test. 



The constant handling of lead compounds is also one of the 

 causes of lead-poisoning (painters' colic). 



As an antidote, magnesium sulphate should be used, which 

 forms with lead an insoluble sulphate; the purgative action 

 of magnesia is also useful. 



