ADDKESS. 17 



Vated to only a coinparatively small extent. Tlie most important colour- 

 ing matters recently introduced are the azo-scarlets. They have called 

 into use the coal-tar hydrocarbons, xylene and cumene. Naphthalene 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 preparation 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 naphthalene resulting from the distillation of coal-tar ; and the 

 value of the colouring matter thus produced is estimated by Mr. Perkin 

 at 3,350,000Z. 



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 

 20Z. 10s. a ton, represents an annual value of 1,947,500L 



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 I2s. . . 2,400,000 



Total ... . . £8,370,500 



Taking the coal used, 9,000,000 tons, at 12.s., equal 5,400,000Z. ; it 

 follows that the by-products alone exceed in value the coal used by 

 very nearly 3,000,000?. 



In using raw coal for heating purposes these valuable products are 

 not only absolutely lost to us, but in their stead we are favoured with 

 those semi-gaseous by-products in the atmosphere too well known to the 

 denizens of London and other large towns as smoke. Professor Roberts 

 has calculated that the soot in the pall hanging over London on a 

 winter's day amounts to fifty tons, and that the carbon present as 

 hydrocarbons and in the half-burnt form of carbonic oxide, a poisonous 

 compound, resulting from the imperfect combustion of coal, may be 

 taken as at least five times that amount. Mr. Aitken has shown, 

 moreover, in an interesting paper communicated to the Royal Society of 



1882. c 



