I. INTRODUCTION 7 



eventually leads to the more or less complete oxidation of the carbon 

 in the food consumed and the consequent production of carbon 

 dioxide, the characteristics of a plant's vital processes are the separa- 

 tion of carbon from carbon dioxide and the formation of less oxidised 

 carbon compounds. 



The former process is attended by the liberation of energy in the 

 form of heat and mechanical work, the latter by an absorption and 

 storing up of energy received in the form of light. 



Carbon is remarkable for its power of uniting in a vast number of 

 proportions with hydrogen and with hydrogen and oxygen. This 

 power is pictured by the chemist as being due to the atoms of carbon 

 possessing a tendency to link themselves together. 



To take a simple case, there are several series of hydrocarbons 

 known, of which the following may be taken as representatives : 



The Paraffin Series. The Olefine Series. 



H 



H C H 

 CH 4 or H C H C 2 H 4 or || 



H C H 

 H 



H H C H 



I II 



H C H H C 



C 2 H ( . or C-H, or 



H C H H C H 



H H C H 



I II 



H C H C H 



C,H 8 or H C H C 4 H 8 or H C H 



H C-H H C H 



^ A 



etc. etc. 



In each of these two series it will be observed that every 

 member differs from the one preceding it by CH 2 and its graphical 

 formula is written by simply adding a carbon atom attached to two 

 hydrogen atoms between the terminal groups in the chain. A similar 

 power of linking together is shown by the carbon atoms in other 

 carbon compounds. It will be noted, from the examples given, that the 

 linkage of two carbon atoms together may be by one or by two of their 

 combining affinities. 



The presence of one pair of doubly linked carbon atoms is the 

 characteristic of the olefine series. In another, the acetylene series, 

 trebly linked carbon atoms occur, e.g., HC== CH, acetylene itself. It 

 is to this power of the carbon atoms of linking themselves together that 

 the possibility of the existence of such an immense number of carbon 

 compounds is due. No other element shows the same power, unless it 



