> I 



6 ORGANIC AGRICULTURAL CHEMISTRY 



ing point for the development of our study. As these com-i 

 pounds consist of the two elements, hydrogen and carbon, they 

 are known as hydro-carbons. The hydrocarbons themselves 

 are not found in either plants or animals. A few compounds 

 of hydrogen and carbon do occur as plant constituents, e.g. 

 turpentine, but these do not belong to the primary group of 

 hydrocarbons. 



The hydrocarbons are, however, a product of the decom- 

 position of plant or animal substances. Plant and animal 

 bodies consist largely of complex compounds of the elements 

 carbon, hydrogen, oxygen, nitrogen, and sometimes sulphur 

 and phosphorus. These compounds on decomposing, either 

 by slow natural processes, as have taken place geologically in 

 the formation of coal and petroleum, or by rapid artificial pro- 

 cesses as in the distillation of wood, break down and yield 

 eventually much more simple compounds. In the artificial dis- 

 tillation, some of the compounds obtained, e.g. wood alcohol 

 and acetic acid, still contain carbon, hydrogen and oxygen, 

 while others are gases containing carbon and hydrogen only, 

 part of the oxygen going off in the form of water (H2O). The 

 nitrogen is volatilized in the form of ammonia or ammonia-like 

 compounds containing also carbon and hydrogen. In the nat- 

 ural geological decomposition of plant and animal substances 

 the greater part of the carbon and hydrogen, however, remains 

 in coal and petroleum and is easily volatilized from them, in 

 the form of compounds containing only these two elements. 

 Therefore we may say that petroleum, natural gas, coal and the 

 gases formed by the natural decomposition of plant remains 

 {marsh gas) , all contain, or at least yield by distillation, products 

 which contain true hydrocarbons. 



Although there are different theories as to the origin of such 

 substances as petroleum, we may consider it as probably true 

 that some at least of the petroleum and other materials, which 

 are the sources of hydrocarbons, have been produced by the 

 decomposition of plant and animal bodies from which the 

 carbon and hydrogen have been derived. 



