HYDROCARBONS 53 



there is no reaction, unless the commercial mixture of hydrocarbons 

 contain hydrocarbons belonging to the unsaturated series. 



They are acted upon by the halogens forming substitution products 

 (P. -57). 



Synthetical Preparation. 



1. The lower members of the series can be prepared by the action 

 of water on certain metallic carbides, e.g. : 



Marsh gas is evolved if about 2 gm. of aluminium carbide in a test 

 tube be covered with water. The gas may be collected in an inverted 

 test tube and shown to be inflammable. 



2. Saturated hydrocarbons can be prepared by the dry distillation 

 of the dry sodium salt (i part) of a fatty acid with soda lime (3 parts). 



E.g. Methaneiis given off when fused sodium acetate and soda lime 

 in the above proportions are heated together in a test tube. The 

 evolved gas may be ignited at the mouth of the tube. 

 CH 3 COONa + NaOH = CH 4 + Na 2 CO 3 . 



3. Saturated hydrocarbons are prepared from the correspond- 

 ing halogen derivative by reduction with hydriodic acid, zinc-copper 

 couple, zinc and hydrochloric acid, etc. 



C 2 H 5 I + HI = C 2 H 6 + I 8 



4. The higher members of the series are prepared from the lower 

 members by treating the dry halogen derivative (alkyl halide) with zinc 

 or with sodium : 



CHJ + aNa + CH 3 I = CH 3 . CH 3 + 2 NaI 

 2CH 8 I+ Zn = CH 8 .CH 8 + Znl a . 



