MOLECULAR STRUCTURE AND LIFE PICTET. 207 



they take place. If the plant be left to itself in the open air its 

 nitrogenous materials at once undergo rapid putrefaction with the 

 formation of ammonia, which is restored to the soil, and carbonic 

 acid, which returns to the atmosphere. The nonnitrpgenous mate- 

 rials, and in particular cellulose, resist much longer, but they also 

 finally disappear, due to a slow combustion of which the agent, 

 either direct or indirect, is the oxygen of the air. 



If the dead plant, instead of being left in the open air, is more 

 or less covered with earth, this action of the oxygen is retarded, 

 and the formation of earth molds are aided, substances very little 

 known from the viewpoint of chemistry but concerning which we 

 do know they are products of the incomplete oxidation of cellu- 

 lose and present some characteristics of phenol, that is, of cyclic 

 compounds. 



If, finally, these same vegetable materials are entirely protected 

 from the action of the air, either by submersion in water or by being 

 buried deep in the earth, as occurs in great geological displacements, 

 they undergo none the less a slow transformation. But this is no 

 longer an oxidation, it is a decomposition of a special character, the 

 principles and agencies of which we do not Imow, although we do 

 know perfectly the final products. These are our fossil fuels of 

 various ages, as lignite and bituminous and anthracite coals. There 

 is no doubt that in this instance it is cellulose which furnishes the 

 essential material of coals. In this transformation the cellulose 

 loses a part of its oxygen and hydrogen, and is consequently enriched 

 in carbon. But this decomposition taking place at low temperature, 

 Liffects only the periphery of the molecule; the carbon nucleus is not 

 affected. It must therefore be admitted that the fundamental struc- 

 ture is the same in coal as in cellulose, and that detemiining it in the 

 former establishes it at the same time in the latter. 



Unfortunately, though coal has been used for two centuries as a 

 fuel, though for a hundred years there have been obtained from it by 

 distillation three products of such great industrial importance as 

 illuminating gas, coal tar, and coke, yet there remains an almost total 

 ignorance of its chemical nature. Can you infer its nature from the 

 products of this distillation? It is known, as I have said, that coal 

 tar is formed exclusively of cyclic compounds. It is the same with 

 coke. The fact that it furnishes aromatic acids by distillation as- 

 sures us that the atoms of carbon which compose it are united in 

 closed chains. Can it be said that the same structure may be at- 

 tributed to the materials as to their derivatives? Such an inference 

 would seem to be absolutely unjustified, because during the distilla- 

 tion of coal these materials have been subjected to temperatures of 

 800° to 1,000°, and we are told by Berthelot's experiments that these 

 temperatures are the cause of the cyclisation of all the open chains. 



