HYDROCARBONS. 



305 



A mixture of the highest and solid members of the paraffin series 

 distilling at a temperature about 350 C. (662 F.) is known as 

 paraffin, a white, crystalline substance used for candles, etc. ; it fuses 

 at about 75 C. (167 F.). 



Illuminating- gas is a mixture of gases obtained by the destructive 

 distillation of coal (or wood) in iron retorts, with subsequent purifica- 

 tion of the gases generated. The constituents of coal have been men- 

 tioned above. The products formed from it during its destructive 

 distillation are very numerous ; the following are the most important: 



The gases are purified by condensing ammonia (and some other 

 gases) in water, carbon dioxide and hydrosulphuric acid in calcium 

 hydroxide. The following is the composition of a purified illumi- 

 nating gas obtained from cannel-coal : 



Hydrogen 46 volumes. 



Methane 41 " 



Ethene 6 " 



Carbonic oxide 4 " 



Carbon dioxide 2 " 



Nitrogen 1 volume. 



Experiment 42. Use apparatus shown in Fig. 5, page 37. Fill the combus- 

 tion-tube A with sawdust (almost any other non-volatile organic matter may be 

 used), apply heat and continue it as long as gases are evolved. Notice that by 

 this process of destructive distillation are formed a gas (or gas mixture), which 



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