THE VOLATILE PART OF PLANTS. 39 



Nitrogen cannot maintain respiration, so that animals 

 perish if confined in it. For this reason it was formerly- 

 called Azote (against life). Decay does not proceed in an 

 atmosphere of this gas, and in general it is difficult to ef- 

 fect its direct union with other bodies. At a high tem- 

 perature, especially in presence of baryta, it unites with 

 carbon, forming cyanogen — a compound existing iu Prus- 

 sian-blue. 



The atmosphere is the great store and source of nitrogen 

 in nature. In the mineral kingdom, especially in soils, 

 it occurs in small quantity as an ingredient of saltpeter 

 and ammonia. It is a small but constant constituent of 

 all plants, and in the animal it is a ne\'er-failing component 

 of the working tissues, the muscles, tendons and nerves, 

 and is hence an indispensable ingredient of food. 



Hydrogen I— Water, which is so abundant in nature, 

 and so essential to organic existence, is a compound of 

 two elements, viz. : oxygen, that has already been con- 

 sidered, and hydrogen, which we now come to notice. 



Hydrogen, like oxygen, is a gas, destitute, when pure, 

 of either odor, taste, or color. It does not occur naturally 

 in the free state, except in small quantity in the emana- 

 tions from boiling springs and volcanoes. Its preparation 

 almost, always consists in abstracting oxygen from water 

 by means of agents which have no special affinity for hy- 

 drogen, and therefore leave it uncombined. 



8odium, a metal familiar to the chemist, has such an at- 

 traction for oxygen that it decomposes water with great 

 rapidity. 



Exp. 11. — Hydrogen is therefore readily pi'ocured by inverting a bot- 

 tle full of water iu a bowl, and inserting into it a bit of sodium as large 

 as a pea. The sodium must first be wiped free from the naphtha in 

 which it is kept, and then be wrapped tightly in several folds of paper. 

 On bringing it, thus prepared, under the mouth of the bottle, it floats 

 upward, and when the water penetrates the paper, an abuudaut escape 

 of gas occurs. 



Metallic iron and zinc decompose water, uniting with 

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