LEAD. 



113 



The oxides of lead are easily changed into glass, 

 and unite with all the metals except gold and silver; 

 on this account they are employed for separating 

 other metals from these. This process is called 

 cupellation. The mixed metal is put into a dish 

 called a cupel, made of bone-ashes, and placed in a 

 cupelling furnace ; the lead is oxidized and vitri- 

 fied, and sinks into the bone-ash cupel, carrying 

 with it all the baser metals. 



White lead, so much used in painting, is a com- 

 pound of the yellow oxide and carbonic acid ; or a 

 carbonate of lead. It is made by exposing plates of 

 pure lead to the warm vapour of vinegar. By this 

 they are gradually corroded, and converted into a 

 heavy white powder, which is white lead. 



When the carbonate of lead is dissolved in dis- 

 tilled vinegar, a salt is obtained, which crystallizes, 

 and is called commonly sugar of lead; more pro- 

 perly acetate of lead. All the salts of lead have a 

 sweetish taste, and are of a poisonous quality. 



The affinity of the muriatic acid (hydrochloric 

 acid) for the oxides of lead is so great, that the 

 latter decomposes all the combinations of this acid. 

 They decompose the muriate of soda (common salt), 

 and thus form muriate of lead, which, on fusion, 

 affords mineral or patent yellow. 



Sulphuric acid does not act on lead when cold; 

 but dissolves it at a boiling heat, and forms sul- 

 phate of lead, which is insoluble in water. 



Chromate ofkad y or chromic acid and lead, is a 

 very beautiful yellow pigment. It is found native 

 in small quantities, but is now prepared largely by 

 art. Lead is one of the most useful metals. It 

 is much employed in covering houses, when made 

 into thin sheets by casting or by milling. It is used 

 also for water-pipes and cisterns, and for a variety 



VOL. II. I 



