SfK WILLIAM SIEMENS, F.R.S. 337 



tious connected with tar-distilling. The success of the alizarine 

 made in this manner has been so great that it has almost entirely 

 superseded the use of madder, which is now cultivated to only a 

 comparatively small extent. The most important colouring 

 matters recently introduced are the azo-scarlets. They have 

 callnl into use the coal-tar hydrocarbons, xylene and cumene. 

 Naphthaline is also used in their preparation. These splendid 

 dyes have replaced cochineal in many of its applications, and have 

 thus seriously interfered with its use. The discovery of artificial 

 indigo by Professor Baeyer is of great interest. For the prepara- 

 tion of this colouring matter toluene is required. At present 

 artificial indigo does not compete seriously with the natural 

 product ; but should it eventually be prepared in quantity from 

 toluene, a further stimulus will be given to the coal-tar trade. 



The colour industry utilises even now practically all the benzene, 

 a large proportion of the solvent naphtha, all the anthracene, and 

 a portion of the naphthaline resulting from the distillation of coal- 

 tar ; and the value of the colouring matter thus produced is 

 estimated by Mr. Perkin at 3,350,000?. 



The demand for ammonia may be taken as unlimited, on account 

 of its high agricultural value as a manure ; and, considering the 

 failing supply of guano and the growing necessity for stimulating 

 the fertility of our soil, an increased production of ammonia may 

 be regarded as a matter of national importance, for the supply of 

 which we have to look almost exclusively to our gasworks. The 

 present production of 1,000,000 tons of liquor yields 95,000 tons 

 of sulphate of ammonia ; which, taken at 20/. 10s. a ton, repre- 

 sents an annual value of 1,947,500?. 



The total annual value of the gasworks' by-products may be 

 estimated as follows : 



Colouring matter 3,350,000 



Sulphate of ammonia . . . . . 1,947,500 



Pitch (325,000 tons) .... 365,000 



Creosote (25,000,000 gallons) . . . 208,000 



Crude carbolic acid (1,000,000 gallons) . 100,000 

 Gas coke, 4,000,000 tons (after allowing 

 2,000,000 tons consumption in working 



the retorts) at 12s 2,400,000 



Total 8,370,500 



VOL. III. Z 



