768. Why does iron rust rapidly when wetted?
Because the water contains a large proportion of oxygen, some of which combines with the iron and forms an oxide of iron, which is rust.
769. Why does stagnant water become putrid?
Because the large amount of oxygen which it contains accelerates the decomposition of dead animal and vegetable substances that accumulate in it.
770. Is there danger in drinking water on account of the living animalcules which it contains?
No danger arises from the living creatures in water; but putrefactive matters may produce serious diseases.
771. What is the best method of guarding against impurities?
By obtaining water from the purest sources, and by filtering it before drinking, by which nearly all extraneous matters would be separated from it.