THE ATMOSPHERE. 



only in containing thirtyseven per cent, of oxigen, instead 

 of twentyone per cent. 



Aqua-fortis, or nitric acid, is composed of the same 

 ingredients with the atmosphere, and owes its great pow- 

 er in corroding almost every thing it touches, to the seven- 

 tyfive per cent, of oxigen it contains. 



A few drops of this acid would certainly and suddenly 

 destroy life, while the atmosphere is essential to sup- 

 port it. 



II. Oxigen supports combustion. Every child knows 

 that fire will not burn without air. But some kinds of 

 air will instantly extinguish it. Whenever we see com- 

 bustion going on, whether in a candle, a common fire, or 

 in the burning of a city, we may know that oxigen is 

 present, and is the principal agent in producing the light, 

 the heat, or the terror. If a burning body be confined 

 in a small portion of atmosphere, it will continue to burn 

 until the oxigen is consumed, when it will go out. Any 

 one may prove this by a simple and useful experiment. 

 Place the small portion of a candle upon a piece of cork 

 or other light body, and let them float upon water in a 

 basin. While the candle is burning, invert a pint or 

 quart glass, so as to enclose it, and entirely exclude the 

 atmosphere. The flame will continue until the oxigen is 

 consumed, when it will be extinguished, and the water 

 rise so as to occupy about one fifth part of the glass, or the 

 portion which was before occupied by oxigen. This ex- 

 periment illustrates two principles ; first, that oxigen is 

 essential to the existence of combustion ; and second, 

 that it constitutes about one fifth of the atmosphere. 



It is to supply the fire with a greater quantity of oxigen, 

 that the bellows is used. It is to exclude oxigen from 

 burning coals, that they are covered with ashes, to pre- 

 serve them alive when left. While enough air is admit- 

 ted to continue the coals in a state of ignition, the quanti- 

 ty is not sufficient to carry on the combustion with any 

 rapidity; consequently the fire is not extinguished, nor 

 the Coals consumed. 



If pure oxigen be thrown upon a burning body, it in- 

 stantly increases the power of the combustion. If a can- 

 dle, just extinguished, be immersed in a vessel containing 



