592 LEAD. 



In the old or Dutch mode of preparing white lead,, which is 

 still extensively practised, thin sheets of the metal are placed 

 over gallipots containing weak acetic acid (water with about 

 2| per cent dry acid), themselves imbedded in fermenting tan, 

 of which the temperature varies from 140 to 150. The action 

 is often very rapid, and the metal disappears in a few weeks to 

 the centre of the sheet. In this process from two to two and 

 a half tons of lead (4480 to 5600 pounds) are converted into 

 carbonate, by a quantity of vinegar which does not contain more 

 than the small quantity of 50 pounds of dry acetic acid. Hence 

 the metal is certainly neither oxidised nor carbonated in this 

 process, at the expense of the acetic acid. The oxygen must 

 be derived from the air, and the carbonic acid from the fer- 

 menting tan. In the newer process, litharge, without any pre- 

 paration, is mixed with water and about 1 per cent of acetate of 

 lead, and carbonic acid gas sent over it ; the oxide of lead is 

 rapidly converted into excellent ceruse. There can be little 

 doubt that all the oxide of lead is successively dissolved by the 

 acetate, and presented to the carbonic acid as a soluble subace- 

 tate ; a compound which, it is known, absorbs carbonic acid with 

 the greatest avidity, and allows its excess of oxide to precipitate 

 as carbonate of lead. The new process supplies likewise the 

 theory of the old one, the function of the acetic acid being ma- 

 nifestly the same in both processes. Nitrate of lead has been 

 substituted for the acetate, with other things the same as in the 

 last process. 



Sulphate of lead ; PbO, SO 3 ; 1895.66 or 151.90. This salt 

 falls when sulphuric acid or a soluble sulphate is added to a 

 solution of acetate or nitrate of lead, as a white dense insoluble 

 precipitate, which appears by the microscope to be composed of 

 minute crystals. Sulphate of lead contains in 100 parts, 26.44 

 sulphuric acid and 73.56 oxide of lead, and may be exposed to a 

 red heat without decomposition. Mr. Richardson finds that 

 this salt acquires considerable opacity, and may be substituted 

 for ceruse, when prepared in a mode analogous to the new 

 process for that substance ; namely by supplying sulphuric acid, 

 in a gradual manner, to a thick mixture of litharge and water, 

 containing a small proportion of acetate of lead. The sulphate 

 of lead may be obtained thus, having any desirable excess of 

 oxide of lead. 



Nitrate of lead; PbO, NO 5 ; 2071.53 or 165.99. Is obtained 



