252 CONSIDERATION OF CARBON COMPOUNDS. 



other words, a complex molecule is split up into two. or more 

 molecules less complex in composition. 



Otherwise, the products formed show a great variety of prop- 

 erties; some are gases, others volatile liquids or solids, some are 

 neutral, others basic or acid substances. In most cases of de- 

 structive distillation a non-volatile residue is left, which is nearly 

 pure carbon. 



Action of oxygen upon organic substances. Combustion. Decay. 

 All organic substances are capable of oxidation, which takes 

 place either rapidly with the evolution of heat and light and is 

 called combustion, or it takes place slowly without the emission 

 of light, and is called slow combustion or decay. The heat gen- 

 erated during the decay of a substance is the same as that 

 generated by burning the substance, but as this heat is liberated 

 in the first instance during weeks, months, or perhaps years, so 

 little heat is produced at a time that it can scarcely be noticed. 



No organic substance found or formed in nature contains a 

 sufficient quantity of oxygen to cause the complete combustion 

 of the combustible elements (carbon and hydrogen) present; by 

 artificial processes such substances may, however, be produced, 

 and are then either highly combustible or even explosive. 



During common combustion, provided an excess of atmos- 

 pheric oxygen be present, the total quantity of carbon is con- 

 verted into carbon dioxide, hydrogen into w 7 ater, sulphur and 

 phosphorus into sulphuric and phosphoric acids, while nitrogen 

 is generally liberated in the elementary state. 



During the process of decay the compounds mentioned above 

 are finally produced, although many intermediate products are 

 also generated. For instance: If a piece of wood be burnt, 

 complete oxidation takes place; intermediate products are also 

 formed chiefly in consequence of the destructive distillation 

 of a portion of the wood, but they are consumed almost as fast 

 as they are produced, as was mentioned in connection with 

 the consideration of flame. Again, when a piece of wood 

 is left exposed to the action of the atmosphere, it slowly burns 

 or decays. The intermediate products formed in this case are 

 entirely different from those produced during common com- 

 bustion. 



Common alcohol has the composition C 2 H 6 ; in burning, it 



