6 NITEOGEN CAEBON 



pounds to build up their tissues. Compounds containing nitrogen 

 therefore are essential ingredients in the food supply of both plants 

 and animals. Many powerful medicines and poisons contain nitrogen, 

 e.g., prussic acid (HCN) and all the alkaloids, of which strychnine 

 (C 21 H 22 N 2 O 2 ), quinine (C 20 H 24 N 2 O 2 ), and morphine (C 17 H 19 NO 3 ) may be 

 given as types. Many nitrogen compounds are extremely unstable 

 and readily split up into simpler bodies, the nitrogen being gener- 

 ally set free; they are often violently explosive, e.g., nitroglycerine, 

 C 3 H 5 (NO 3 ) 3 , and gun cotton, C 6 H 7 O 2 (N0 3 ) 3 . 



We thus see that while free nitrogen is of comparatively little value, 

 its compounds are of the utmost importance to all living beings. Con- 

 sequently, the means of utilising nitrogenous compounds and of pre- 

 venting their waste, often leading to the liberation of the comparatively 

 useless free nitrogen, are matters of intense interest and great im- 

 portance. By some chemists it is thought that supplies of nitrogen 

 compounds will fail us long before the want of phosphates, potash, 

 or other fertilising substances becomes felt. 1 



It is to be hoped that by means of the nitrogen -fixing bacteria 

 which grow in nodules upon the root hairs of certain leguminous 

 plants, or in some other way, it may be found possible to abstract 

 from the atmosphere sufficient nitrogen to supply the wants of both 

 plants and animals for many centuries. Nevertheless, the rapid ex- 

 haustion of our deposits of nitrates and the enormous quantities of 

 valuable nitrogenous materials which are allowed to run to waste in 

 the sewage of our large cities are serious matters for consideration as 

 affecting the future supplies of this indispensable combined nitrogen. 



Carbon is, perhaps, more than any of the other elements, associated 

 with the processes of life. It constitutes a large proportion by weight 

 of the solid portions of all animals and plants. In the mineral kingdom 

 it is also abundant, occurring in immense quantities in carbonates, 

 e.g., those of calcium, magnesium, iron, zinc, lead and copper. It 

 also occurs in the air in the form of carbon dioxide, the amount of 

 which, though small relatively to the other constituents of air, is, ab- 

 solutely, considerable and is constantly being renewed. 



The properties of the three allotropic forms of carbon are fully 

 described in any general textbook of chemistry. They are not of any 

 particular importance from our present standpoint. Much more im- 

 portant are the numerous compounds which carbon forms, especially 

 with hydrogen and oxygen, and with hydrogen, oxygen and nitrogen. 

 Indeed, it is with these compounds of carbon that almost all the 

 chemistry of the nutrition of animals and plants is concerned, other 

 substances taking part in vital processes (though quite essential) being 

 small in amount. 



But although animal life and plant life are both concerned with 

 the chemical changes of carbon compounds, yet they stand towards 

 carbon in an essentially different aspect, for while the life of an animal 



1 Sir W. Crookes, President's address, British Association for Advancement of 

 Science, 1898. 



