LEAD IN WATER. 137 



by further heating red lead under the influence of air, 

 but which is easily made by acting on red lead by 

 nitric acid ; the lead then acquires a third portion of 

 oxygen and becomes a dark brown peroxide. 



311. Of these three oxides, only one, the protoxide, 

 is a base ; the other two oxides, when acted on by 

 acids, part with a portion of their oxygen, and pass 

 into the state of protoxide before they can combine 

 with the acid. The most important of the salts of 

 lead is the carbonate, or white lead, a substance 

 better suited than any other which is known for the 

 manufacture of white paint; it is made either by 

 decomposing a soluble salt of lead by an alkaline 

 carbonate, or by exposing lead to the action of the 

 vapor of vinegar and carbonic acid gas. The acetate 

 of lead, likewise, is manufactured on a large scale, 

 and used for various purposes in the arts. 



312. Lead has a strong affinity for sulphur, and 

 in consequence of this most of the salts of lead are 

 decomposed by sulphuretted hydrogen ; the blacken- 

 ing of white paint is due to this cause. As the sul- 

 phuret of lead is decomposed by chlorine, white paint 

 thus blackened maybe cleaned by muriatic acid; this 

 converts the black sulphuret into a white chloride, 

 though it never looks so white as the carbonate did 

 before. 



313. Lead is acted on by pure water in a very re- 

 markable way, being oxidized and dissolved with great 

 facility; this is not the case with common water con- 

 taining salts of lime, &c. (75). Rain-water, or very 



12* 



