CHAPTER XXII. 



ILLUMINATING GAS, ANILINE DYES AND RESINS. 



ILLUMINATING gas is one of the products of the destructive 

 distillation of coal. The coal is heated in earthenware retorts 

 without access of air till all the volatile matters are driven off, 

 leaving only gas carbon and coke in the retort. The volatile 

 products passing through water and coolers loses ammoniacal 

 liquids and tarry matters by condensation, then through beds of 

 lime or the ferric hydrate, which removes the sulphur and car- 

 bon dioxide, and thence to the gasometer. The gas in the 

 meter consists of marsh gas, hydrogen and carbon monox- 

 ide, with some vapor of benzole, olefiant gas and other hydro- 

 carbons. 



The ammoniacal liquids are the main source of ammonia and 

 the ammonium salts. The coal tar contains, or is made up of 

 many substances which are volatilized at different temperatures. 

 The first to pass over is water with salts of ammonia in solution, 

 then a brown, oily liquid, lighter than water, containing benzole 

 toluole, etc., then a yellow oil heavier than water, containing 

 napthaline, aniline, carbolic acid, etc., and a black residue called 

 pitch remains, which is employed in making Brunswick black and 

 asphalt for paving. The benzole from the light oil is a colorless 

 liquid with the odor of coal gas. The fact of its dissolving 

 caoutchouc and gutta percha, and that it removes grease from 

 cloth and other objects, makes it a valuable substance. 



The chief purpose to which benzole is devoted is the prepara- 

 tion of aniline, which may be converted into the brilliant dyes 

 now so extensively used. Benzole treated with nitric acid forms 

 a dark red liquid from which water precipitates a yellow oily 

 liquid called nitrobenzole. Benzole, C 6 H 6 +HN0 3 =C 6 H 5 (N0 2 ) , 

 nitrobenzole. When nitrobenzole is treated with sulphuric acid 



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