302 CONSIDERATION OF CARBON COMPOUNDS. 



interior of the earth, and by the destructive distillation of various 

 organic matters. Methane is of special interest, because it is the 

 compound from which thousands of other substances are derived. It 

 may be made by the action of inorganic substances upon one another; 

 for instance, by passing a mixture of steam and carbon disulphide 

 over copper heated to red heat, when the following change takes 



place : 



6Cu + CS 2 + 2H 2 = 2Cu 2 S + 2CuO + CH 4 



Bearing in mind that carbon disulphide, as well as water, may be 

 obtained by direct union of the elements, it is evident that methane 

 may be formed indirectly, by means of the above method, from the 

 elements carbon and hydrogen. 



Experiment 40. Use apparatus shown in Fig. 5, page 37, omitting the bent 

 tube B. Mix in a mortar 20 grammes of sodium acetate with 20 grammes of 

 potassium (or sodium) hydroxide and 30 grammes of calcium hydroxide ; fill 

 with this mixture the tube A, which should be made of glass fusing with 

 difficulty, or of so-called "combustion tubing;" apply heat and collect the gas 

 over water. The decomposition takes place thus : 



NaC 2 H 3 O 2 -f- NaOH =a Na 2 CO 3 -f CH 4 . 



Ignite the gas, and notice that its flame is but slightly luminous. Mix some 

 of the gas in a wide-mouth cylinder, of not more than about 200 c.c. capacity, 

 with an equal volume of air and ignite. Eepeat this experiment with mixtures 

 of one volume of methane with 2, 4, 6, 8, and 10 volumes of atmospheric air. 

 Which mixture is most explosive, and why ? How many volumes of oxygen 

 and how many volumes of atmospheric air are needed for the complete com- 

 bustion of one volume of methane ? 



Coal. As methane is one of the products generated during the 

 formation of coal, it may be well to consider this process here briefly. 



The various substances classed togther under the name of coal con- 

 sist principally of carbon, associated with smaller quantities of hydro- 

 gen, oxygen, nitrogen, sulphur, and certain inorganic mineral matters 

 which compose the ash. Coal is formed from buried vegetable 

 matter by a process of decomposition which is partly a fermentation, 

 partly a decay, and chiefly a slow destructive distillation, the heat 

 for this latter process being derived from the interior of the earth, or 

 by the decomposition itself. 



The principal constituent of the organic matter furnishing coal is 

 wood (or woody fibre, cellulose), and a comparison of the composition 

 of this substance with the various kinds of coal gradually formed 

 will help to illustrate the chemical change taking place : 



