COMBUSTION. 35 



fires nor lights ; and, indeed, without air neither ani- 

 mals nor plants could live, for it is just as essential 

 to the life of animals as it is to the growth of plants 

 and the burning of coals and candles. 



25. If a lighted candle is put into a large glass bot- 

 tle, and the mouth of the bottle is then stopped up, 

 the candle soon gets dim, and in a short time goes 

 out: the air is no longer able to keep it alight. If 

 we put a second lighted candle into the bottle it will 

 go out immediately. Were a living animal substitut- 

 ed for the lighted candle, after living for a certain 

 time in a confined portion of air, it would die, and 

 a second animal placed in the air would immediately 

 expire. 



26. The question now will naturally arise : Is the 

 whole of the air, then, spoiled or used up ; and if it is, 

 why does not fresh air enter the bottle and supply its 

 place? The truth is, only a small portion, about one- 

 fifth of the bulk of the air, is able to feed the flame 

 of a candle; the remainder, which cannot feed flame 

 nor the life of an animal, is of a difi*erent kind from 

 the air which can ; and we find that the common air 

 which we breathe is a mixture of two kinds of air, or 

 GAS, as it is called by chemists ; — the one kind, which 

 we might call good air, which supports the life of 

 animals, and is essential to the burning of fires and 

 candles: and the other, or bad air, in which animals 

 cannot live, and which immediately puts out fire 

 and lights. 



^7. Chemists call the good air Oxygen, and the 



