192 BOARD OF AGRICULTURE. [Jan., 



water. The burning of the phosphorus will simply consume the 

 oxygen and leave the hydrogen. It is one thirty-sixth part lighter 

 than common air, and will not support combustion or animal life; 

 a lighted candle placed in it is immediately extinguished. 



The third component of our air is carbonic acid. It is a gas, 

 void of color, but possesses a slight odor and is perceptibly sour 

 and pungent to the taste. It is not a simple element, but a com- 

 pound — carbon united with oxygen. Burning substances are in- 

 stantly extinguished and animals cease to breathe when introduced 

 into it. It is one-half heavier than common air, and is frequently 

 found in the bottom of wells and mines, where it becomes confined 

 and cannot be diffused, and often suffocates workmen who descend 

 into it. The effervescent qualities of soda-water, fermented wines, 

 and mineral waters are due to this gas. It is a varying constituent 

 of the air owing to localities, character of vegetation, animal res- 

 piration, combustion, etc. It is greater at a distance from the 

 earth than at the lower ranges, occasioned by plant respiration, if 

 it may be so called. It may usually be stated to be one gallon in 

 2,500. 



Carbonic acid may be easily prepared by pouring dilute muri- 

 atic acid upon chalk or limestone; the gas rises in the vessel 

 through the liquid, but remains at the bottom, owing to its weight. 

 As it collects it gradually ascends, and finally pours over the edge 

 of the vessel as water would do. Its rise may be shown by intro- 

 ducing two- lighted tapers, one above the other; the lower one will 

 be extinguished first, and in a few moments the upper. 



The fourth constituent of the air, watery vapor, is the steam or 

 vapor of water which comes from the evaporation of lakes and 

 streams, and from the surface of the earth. 



In reconsidering one point in relation to all these gases, namely, 

 weight, we are surprised to see at first how we are to have any 

 atmosphere, for we have in nitrogen a very light gas -^^ part 

 lighter than common air; in oxygen a gas ^ part heavier; and in 

 carbonic acid a very heavy gas ^ heavier than the atmosphere. 

 Why then have we any life sustaining atmosphere at all? Why is 

 it that they do not maintain a just equilibrium, one above another, 

 the deadly carbonic acid at the bottom preventing all animal or 

 vegetable life? Here comes .in one of the most beautiful and 

 beneficent laws of nature, known in science as '' the law of gase- 



