466 CONSIDERATION OF CARBON COMPOUNDS. 



tion, so that we have of the seventh member 9, of the tenth 75, and of the 

 thirteenth member 80<>, possible isomeric hydrocarbons. 



Methane, CH 4 (Marsh-gas, Fire-damp). This hydrocarbon has 

 been spoken of in Chapter 14, where it was stated that it is a color- 

 less, combustible gas, which is formed by the decay of organic matter 

 in the presence of moisture, during the formation of coal in the 

 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 the action of water on aluminum carbide, a compound 

 of the metal aluminum, and carbon, A1 4 C 3 , the following change tak- 

 ing place : 



A1 4 C 3 + 12H 2 = = 3CH 4 + 4A1(OH) 3 . 



Bearing in mind that aluminum carbide, 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 51. Use apparatus shown in Fig. 35, page 87, 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 + NaOH = NajCOg + 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 ? 



Ethane, C-^Hg, is a constituent of natural gas and of crude petroleum. It 

 can be obtained from methane by first replacing in it a hydrogen atom by 

 iodine, when iodo-methane, or methyl-iodide, CH 3 I, is formed, which, when 

 acted on by sodium, is decomposed thus: 



CH 3 I + CH 3 I + 2Na = 2NaI + C 2 H fi . 



This formation of ethane illustrates one of the methods for producing by 

 synthesis i. e., for building up more complex from simpler hydrocarbons. 

 Another method, accomplishing the same result, depends on the action of a 



