26 PROPERTIES OF NITROGEN. 



diately escapes, [its specific gravity, by experiment, is 0-0687, air be- 

 ing 1.] It is the element which is employed to give buoyancy to 

 balloons ; and by this great levity and its relations to flame it is readily 

 distinguished from all other known substances. 



Water absorbs it only in very small quantities, 100 gallons taking up 

 no more than about 1^ gallons of hydrogen gas. But, as already ob- 

 served, this gas does not exist in nature in a free state — is not necessary, 

 therefore, to the growth of plants or animals in this state — and hence its 

 insolubility in water is in unison with the general adaptation of every 

 property of every body, to the health and growth of the highest orders 

 of living beings. 



Hydrogen gas is readily obtained from water by putting into it a few 

 pieces of metallic iron or zinc, and adding a little sulphuric acid (oil of 

 vitriol). • Bubbles of the gas are liberated from the surface of the mcti.1, 

 ascend through the water, and may be collected on the surface. 



§ 5. Nitrogen — its proimrlies and relations to vegetable life. 

 Nitrogen is also known to us only in the form of gas. It exists in the 

 atmosphere to the amount of 79 per cent, of its bulk. It is without 

 colour, taste, or smell. Animals and plants die in this gas, and a taper 

 is instantly extinguished when introduced into it ; the gas itself under- 

 going no change. It is lighter than atmospheric air, in the proportion 

 of 97i to 100, [its density is 0-976, air being 1.] It is an essential 

 constituent of the air we breathe, serving to temper the ardour with 

 which combustion would proceed and animals live in iindiiuted oxygen 

 gas. It forms a part of very many animal and of some vegetable sub- 

 stances, but it is not known to enter into the composition of any of the 

 great mineral masses of which the earth's crust is made up. In coal 

 alone, which is of vegetable origin, it has been delected to the amount 

 of one or two percent. It is therefore much less abundant in nature 

 than any of the other so called organic elements — and it exhibits much 

 less decided properties than any of them ; yet we shall hereafter see 

 that it performs certain most important functions in reference both to the 

 growth of plants and to the nourishment of animals. 



One hundred volumes of water dissolve about li volumes of this 

 gas.* Spring and rain waters absorb it as they do oxygen, from the at- 

 mospheric air, and bear it in solution to the roots, by which it is not un- 

 likely that it may be conveyed directly into the circulation of plants. 



Such are the several elementary bodies of which the organic or de- 

 structible part of vegetable substances is formed. With one exception 

 they are known to us only in the form of gases ; and yet out of these 

 gases much of the solid parts of animals and of plants are made up. 

 When alone, at the ordinary temperature of the atmosphere they form 

 invisible kinds of air; when united, they constitute those various forms 

 of vegetable matter which it is the aim and end of the art of culture to 

 raise with rapidity, with certainty, and in abundance. How difficult 

 to understand the intricate processes by which nature works up these 



• Henry De Saussure says, that pure water absorbs 4 per cent, of its bulk of this gas. 



