310 CHEMICAL DISCOVERY AND INVENTION 



the undissolved oil which contains much naphthalene. The tar 

 acids are separated from the caustic soda solution by heating the 

 liquid in the presence of waste carbonic acid gas, and by further 

 treatment pure phenol is obtained. 



Anthracene is a crystalline solid which when pure exhibits a 

 beautiful blue fluorescence. It melts at 213 C., and boils at 

 351 C. Anthracene separates on standing from the crude oil 

 in the form of a greenish crystalline solid which is filtered off, 

 pressed, and washed free from oil by the use of a little solvent 

 naphtha. 



Creosote oil, which is the residuum left after treatment in the 

 manner indicated above, is used on a very large scale as a pre- 

 servative for timber. 



Crude coal-tar finds some applications without being separated 

 by distillation into its components. These are familiar enough. 

 But as the starting point for chemical industry it may be worth 

 while to summarise the chief applications which are made of 

 the chemical compounds isolated from coal-tar. These are given 

 in the following table : 



Benzene 

 Toluene 



Xylenes 

 Naphthalene 



Phenol 

 Anthracene . 



Crude. 



Motor fuel, Solvent. 

 Solvent. 



Solvent Naphtha. 



Insecticide and Mild Anti- 

 septic. 



Strong Antiseptic and Dis- 

 infectant. 



Pure. 



Dyes. 



Dyes. Explo- 

 sive, T.N.T. 

 Dyes. 



Dyes. 



Dyes. Explosive. 

 Dyes. 



CHAPTER XXI 



PRODUCTION OF DYES 



IT is perhaps scarcely necessary to state the fact that coal-tar 

 does not contain ready-formed anything in the nature of a dye, 

 nor anything which possesses colour, except of course the black 

 highly carbonaceous substances which are left after distillation. 

 But that such an idea still lurks in the minds of some people is 

 indicated by the legend formerly current, that Perkin, the 



