1883.] THE VENTILATION OF FARM BUILDINGS. 191 



is not a purely elementary substance — one by itself — but that it is 

 composed of other materials, in fact a mixture of gases and mat- 

 ter, each of which holds an individual relationship towards animal 

 and vegetable life. We find that nearly the whole bulk of it is 

 oxygen and nitrogen, and are in the habit of speaking of it as 

 composed of these two gases; but we also find as regular compo- 

 nents carbonic acid and watery vapor. 



These four substances the air everywhere and always contains, 

 and in very nearly the same proportions. Gay Lussac examined 

 air taken from an altitude of nearly four miles from the earth's 

 surface, and compared it with that from the summit of the Alps, 

 and from deep valleys, and found it to be sensibly the same. The 

 exact and numerous experiments of other analysts have shown the 

 same results. 



Besides these four components there are found traces of ammo- 

 nia, sulphuretted hydrogen, and carburetted hydrogen, but they 

 are very varying and too small for estimation, and we leave them 

 out entirely in our review of the chemical composition of the air. 



Oxygen is an elementary substance; that is, it has never been 

 decomposed; it is a gas without color, taste, or smell. We always 

 speak of it as a gas, but when compressed with a force of three 

 hundred atmospheres and cooled to a low degree it becomes a 

 liquid. Animals breathe in it with a great sense of exhilaration 

 and excitement; it increases the circulation, produces fever and 

 finally death. They live too rapidly in pure oxygen, and burn 

 away as in all processes of combustion. When a lighted candle is 

 introduced into it, the flame at once becomes more brilliant and it 

 is rapidly consumed. 



This gas is easily prepared by mixing an ounce of the chlorate 

 of potash with fifty grains of the oxide of iron, or black oxide of 

 manganese, and heating the mixture in a flask over a spirit-lamp. 

 It is quickly given off, but cannot of course be seen; but by intro- 

 ducing a lighted candle, or a bit of phosphorus on a wire, the 

 brilliant combustion will at once prove the presence of the gas. 

 Oxygen is one-ninth part heavier than common air. 



Nitrogen, like its colleague, is a gas v/ithout color, taste, or smell, 

 and may also be made to assume the liquid form. It is quickly 

 obtained by burning a small piece of phosphorus over water and 

 inverting a gla s beil-jar over it, immersing the lower edge in the 



