ACTION OF WATER ON LEADEN PIPES. 
343 
2. Waters concealed from sunlight, and supplied by 
lixivia t ion through soils or rock, or both, of greater or less 
depth, such as wells and certain springs* 
They differ, (a.) in temperature ; well-water, through a 
large part of the year, is colder than lake, pond or river 
water ; (b.) in the percentage of gases in solution ; recently 
drawn well-water, in summer particularly, parts with a 
quantity of air upon exposure to the surface of the tempe- 
rature. In winter these relationships must to some extent 
be inverted, in high latitudes for a longer, and in lower lati- 
tudes for a shorter period. 
(c.) They differ in the per-centage of inorganic matter in 
solution ; well-waters contain more ; (d.) in the relative pro- 
portions of salts in Solution ; well waters contain more ni- 
trates and chlorides; and (e.) in the per-centage of organic 
matter ; well waters contain less. 
Relations of Lead to Air and Water. — (a.) Lead is not 
oxidated in dry air, or (b.) in pure water deprived of air. 
(c.) It is oxidated in water, other things being equal, in 
general proportion to the amount of uncombined oxygen in 
solution, {d. ) When present in sufficient quantity, nitrates 
in neutral waters are to some extent reduced by lead, (e.) 
Both nitrates and chlorides promote the solution of some 
coats formed on lead. 
(f) Organic matter influences the action of water upon 
lead. If insoluble, it impairs the action by facilitating the 
escape of air ; if soluble, by consuming the oxygen in solu- 
tion, and by reducing the nitrates when present. The green 
plants, so called, the animalcula which evolve oxygen, are 
abundant in open waters in warm weather only, and of 
course when the capacity of water to retain air in solutiou 
is lowest; so that, although oxygen is produced in open 
waters by these microscopic organisms, it does not increase 
the vigor of their action upon lead. 
* Rain-water is to some extent employed as a beverage. It is more 
nearly allied to waters derived from surface-drainage. 
