General ignorance of the constitution of the atmosphere.  The subject briefly explained.  Oxygen gas.  Nitrogen.  Carbonic acid.  Fires, candles, and breathing dependent on oxygen.  Danger from carbonic acid.  How it destroys people.  Impurity of the air by means of lamps and candles.  Other sources of impurity.  Experiment of putting the candle under the bed-clothes.  Covering the heads of infants while sleeping—­its dangers.  Proportions of oxygen and nitrogen in pure and impure air.  No wonder children become sickly.  Particular means of ventilating rooms.  Caution in regard to lamps.  Washing, ironing, cooking, &c., in a nursery.  Their evil tendency.  Fumigation—­camphor, vinegar.

Few people take sufficient pains to preserve the air in any of their apartments pure; for few know what the constitution of our atmosphere is, and in how many ways and with what ease it is rendered impure.

It is not my purpose to go into a learned, scientific account in this place, or even in this work, of the constitution of the atmosphere.  A few plain statements are all that are indispensable.  The atmosphere which we breathe is composed of two different airs or gases.  One of these is called oxygen, [Footnote:  Oxygen gas is the chief supporter of combustion, as well as of respiration.  It is the vital part, as it were, of the air.  No animal or vegetable could long exist without it.  And yet if alone, unmixed, it is too pure and too refined for animals to breathe.  Nitrogen gas, on the contrary, while alone, will not support either respiration or combustion; mixed, however, with oxygen, it dilutes it, and in the most happy manner fits it for reception into the lungs.] and the other nitrogen.  There is another gas usually found with these two, in smaller quantity, called carbonic acid gas; but whether it is necessary, in a very small quantity, to health, chemists, I believe, are not agreed.  One thing, however, is certain—­that if any portion of it is healthful, it must be very little—­not more, certainly, than one-fiftieth or one-hundredth of the whole mass.

It is by means of the oxygen it contains, that air sustains life and combustion.  Were it not for this, neither fires nor candles would burn, and no animal could breathe a single moment.  Breathing consumes this oxygen of the air very rapidly.  When the oxygen is present in about a certain proportion, combustion and respiration go on well, but when its natural proportion is diminished, the fire does not burn so well, neither does the candle; and no one can breathe so freely.

Not only are breathing and combustion impeded or disturbed by the diminution of oxygen in the atmosphere, but just in proportion as oxygen is diminished by these two processes, or either of them, carbonic acid is formed, which is not only bad for combustion, but much worse for health.  If any considerable quantity of it is inhaled, it appears to be an absolute poison to the human system; and if in very large quantity, will often cause immediate death.