WATER* AND ITS IMPURITIES. 
165 
On the Action of Water on Lead. 
Notwithstanding that lead has now been employed for ages 
in the storage and conveyance of water, the principles of its 
action on that substance have been, in general, but ill under- 
stood and defined. Much uncertainty and contradiction have 
prevailed, even amongst scientific men, as to what waters act 
most on lead and what least ; some asserting that soft waters do 
so, and others, that hard waters affect lead most. 
These principles will be found to be in strict accordance with 
the laws of chemical combination. 
In speaking of lead in connexion with water, we commonly 
make use of the phrase, “ the action of water on lead this 
phrase, unless clearly explained, is liable to be associated in 
the mind with error. 
Water, as we before observed, consists of oxygen and 
hydrogen : the only combination, therefore, which could by 
possibility result from the decomposition of water and the 
union of its elements with lead, consists in the formation of the 
hydrated oxide of that metal — an almost insoluble compound. 
But the waters in general use contain several gases and 
salts ; these act on lead in a variety of ways, or, in other and 
more definite words, form various combinations with lead. 
Lastly, water imbibes air and other gases, the oxygen of the 
former combining with the lead, and forming the oxide. 
When, therefore, we speak of the action of water on lead, in 
general terms, water in the condition in which it is commonly 
met with is implied ; but in our scientific inquiries we must 
carefully discriminate between the effects of the action of pure 
water on lead and those effects which result from the presence 
of the salts and gases so commonly contained in water. 
The effect of the action of pure water, then, on lead, sup- 
posing it to be really decomposed, is to give rise to the forma- 
tion of a hydrated oxide, the same body likewise being formed 
as the result of the presence in water of free oxygen derived 
from the atmosphere. 
But in some cases lead does not only exist in water as a 
slightly soluble oxide, but is in a state of chemical solution ; 
and we have now to inquire in what condition it may be sup- 
posed to be in such cases. The most common soluble salt of 
lead detected in water is the carbonate, which consists of car- 
bonic acid in union with the oxide of lead. 
Now an oxide is a body or base in combination with oxygen, 
which readily unites with any free acid with which it may 
come in contact : in a water, therefore, acid from the presence 
of free or uncombined carbonic acid, stored in a leaden vessel, 
