262 CHEMISTEY. 



The commercial white-lead is prepared differently, usually 

 by exposing sheet-lead to the influence of the oxygen of 

 the air in the presence of acetic acid or vinegar. The 

 agency of the acetic acid of the vinegar is interesting. It 

 dissolves successive portions of the oxide of lead, forming 

 with it an acetate, and the moment that it does this the 

 carbonic acid takes away the oxide from it; so that the 

 office of the acetic acid is simply to take the oxide and 

 deliver it over to the carbonic acid. It is very much as 

 the nitric acid in the formation of sulphuric acid ( 242) 

 continually takes oxygen from the air and delivers it over 

 to the sulphurous acid. 



372. Lead-Poisoning. The carbonate of lead is a poison, 

 producing, when introduced into the system, lead colic, 

 paralysis, and many other bad affections. Many persons 

 have been subjected to protracted suffering, and many lives 

 have been lost from this poison. Painters are liable to be 

 poisoned by it, but the liability has been much diminished 

 by precautions in the use of the article in their business. 

 The poisonous influence more often comes from drinking 

 water brought in lead pipes, and in that case is commonly 

 slow and insidious. And, as a general rule, the purer the 

 water, the more apt is it to be rendered poisonous by the 

 lead. The reason of this is obvious. You will remember 

 that we told you that there is always some carbonic anhy- 

 dride in water. Now this acts upon the metallic lead in 

 connection w 7 ith the water, and, forming carbonate of lead, 

 makes it poisonous. It will do so unless there be some- 

 thing to prevent it. If the water be quite pure, there is 

 nothing in it to prevent the carbonic anhydride from thus 

 acting ; but if there be certain impurities, as, for example, 

 sulphate of lime, there will be formed a thin coating over 

 the surface of the metal, which effectually shields it. Lead 

 pipes ought never to be used unless the water to be brought 



