Necessary to continued good health are Good Air, Good Food, and Good Water. It is the object of Sanitary Science to secure these.
CHAPTER I.
AIR.
Normal air contains 79 per cent of nitrogen, 20.96 per cent of oxygen, and .04 per cent (4 parts in 10,000) of carbonic acid.
Oxygen supports animal life; carbonic acid, vegetable life; and the use of the nitrogen, otherwise than as a diluent, is not known.
Very pure air contains 78.98 per cent of nitrogen, 20.99 per cent of oxygen, and .03 per cent of carbonic acid.
Air begins to be very bad when the oxygen is reduced to 20.60 parts in 100. In mines, where candles go out, oxygen is reduced to 18.50 parts in 100, and, in the worst specimen yet examined by Angus Smith, to 18.27. Air in which the percentage of oxygen has been reduced to 17.20 is very difficult to remain in for many minutes.
Aside from impurities due to local causes, the purest air is found from six to forty feet above the ground, and the most impure from seventy to ninety feet, where the air from chimneys is poured forth.
Air is contaminated by the products of respiration and the bodily emanations of healthy persons, and by the products of combustion.
An adult man, in ordinary work, gives off in twenty-four hours from twelve to eighteen cubic feet of carbonic acid, according to his size; women, children, and old persons less.