Coal-tar - 



Solids 



470 CONSIDERATION OF CARBON COMPOUNDS. 



B. P. 



f Benzene .... C 6 H 6 80 



I Toluene . . . C 7 H 8 110 



Liquids -j Aniline C 6 H 5 NH 2 182 



' Acetic acid .... C 2 H 4 O 2 117 



Water H 2 O 100 



Carbolic acid . . . C 6 H 6 O 188 



Kresylicacid . . . C 7 H 8 O 201 



Naphthalene .... C IO H 8 220 



Anthracene .... C U H 10 360 



I Paraffin C 16 H 34 280 



Solid residue : Coke, chiefly carbon and inorganic matter. 



The gases are purified by condensing ammonia (and some other 

 gases) in water, carbon dioxide and hydrogen sulphide 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 " 



Carbon monoxide .... 4 " 



Carbon dioxide 2 " 



Nitrogen 1 volume. 



The poisonous properties of illuminating gas are due chiefly to car- 

 bon monoxide, all other constituents being more or less harmless. 



Experiment 53. Use apparatus shown in Fig. 35, page 87. 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 

 may be ignited, a dark, almost black liquid (tar), which condenses in the tube 

 B, and that a residue is left which is chiefly carbon. The tarry liquid shows an 

 acid reaction, due to acetic and other acids present. 



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

 nating gas, contains, as shown by the above table, many valuable sub- 

 stances, such as benzene, aniline, carbolic acid, paraffin, etc., which 

 are separated from each other by making use of the difference in their 

 boiling-points and specific gravities, or of their solubility or insolu- 

 bility in various liquids, or, finally, of their basic, acid, or neutral 

 properties. 



Unsaturated hydrocarbons. The terms saturated and un- 

 saturated compounds are used for inorganic and organic substances. 

 A compound is said to be unsaturated when it has the power to enter 

 directly into combination with elements or compounds. Thus, car- 



