264 



CONSIDERATION OF CARBON COMPOUNDS. 



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

 tive distillation of coal (or wood) in iron retorts,, with subse- 

 quent purification of the gases generated. The constituents of 

 coal have been mentioned above. The products formed from it 

 during its destructive distillation are very numerous ; the fol- 

 lowing are the most important : 



B. P. 



80 



'no 



132 

 117 

 100 

 188 

 201 

 220 

 360 

 280 

 Solid residue : Coke, chiefly carbon and inorganic matter. 



The gases are purified by condensing ammonia (and some 

 other gases) by means of water, carbon dioxide and hydrosul- 

 pnuric acid by calcium hydrate. The following is the composi- 

 tion of a purified illuminating gas obtained from cannel-coal : 



Hydrogen, 46 volumes. 



Methane, 41 " 



Ethene, 6 " 



Carbonic oxide, 4 " 



Carbon dioxide, 2 " 



Nitrogen, 1 " 



Coal-tar, obtained as a by-product in the manufacture of illu- 

 minating gas contains, as shown by the above table, many 

 valuable substances, such as benzene, aniline, carbolic acid, 

 paraffine, etc., which are separated from each other by making 



