268 Chemistry. [Lecture S3. 



is a true test of the sulphuric acid when com- 

 bined with any substance ; the solution, instead 

 of being saturated with the lead, must have a 

 little redundant acid. The reason is plain, for 

 then the lead will not be precipitated by lime or 

 alkalies, for the acid will saturate them, and 

 prevent its precipitation ; but at the same time 

 does not hinder the action of the lead if there is 

 11 sulphuric acid in the water ; for they always 

 unite, and form a compound incapable of solu- 

 tion in water, and which therefore renders the 

 mixture muddy, and afterwards precipitates. 

 All experiments of this kind should be allowed 

 to rest at least twenty-four hours. 



The solution of lead in the nitrous acid does 

 not disturb the transparency of pure water ; nor 

 will its transparency be disturbed by common 

 salt, or a little of the muriatic acid in its sepa- 

 rate state. Ordinary common salt may render 

 the experiment fallacious, as it contains sulphate 

 of magnesia ; but if we add the least quantity of 

 sulphuric acid, or any of its compounds, the 

 liquor becomes muddy; when this muddiness 

 appears, we must add a small quantity of the 

 nitric acid, to try if the muddiness will disap- 

 pear for an alkali may have precipitated the 

 lead but then it will be in the form of an oxide, 

 the nitric acid will re-dissolve it, and thus the 

 muddiness disappear. If by this and other 

 trials we have learned that die water does: not 

 contain an alkali, and a muddiness takes place, 



