SCIENCE IN RELATION TO THE ARTS. 209 



Coloring-matter 3,350,000 



Sulphate of ammonia 1,947,000 



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 consump- 

 tion in working the retorts) at 12s 2,400,000 



Total 8,370,000 



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

 follows that the by-products 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 favored 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 clay amounts to fifty tons, and that the 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 Edinburgh, last year, that the fine dust resulting from the 

 imperfect combustion of coal is mainly instrumental in the formation 

 of fog ; each particle of solid matter attracting to itself aqueous vapor ; 

 these globules of fog are rendered particularly tenacious and disagree- 

 able by the presence of tar-vapor, another result of imperfect combus- 

 tion of raw fuel, which might be turned to much better account at the 

 dye-works. The hurtful influence of smoke upon public health, the 

 great personal discomfort to which it gives rise, and the vast expense 

 it indirectly causes through the destruction of our monuments, pictures, 

 furniture, and apparel, are now being recognized, as is evinced by the 

 success of recent Smoke Abatement Exhibitions. The most effectual 

 remedy would result from a general recognition of the fact that, wher- 

 ever smoke is produced, fuel is being consumed wastefully, and that 

 all our calorific effects, from the largest down to the domestic fire, can 

 be realized as completely and more economically, without allowing any 

 of the fuel employed to reach the atmosphere unburnt. This most de- 

 sirable result may be effected by the use of gas for all heating purposes, 

 with or without the addition of coke or anthracite. 



The cheapest form of gas is that obtained through the entire distil- 

 lation of fuel in such gas-producers as are now largely used in working 

 the furnaces of glass, iron, and steel works ; but gas of this description 

 would not be available for the supply of towns owing to its bulk, about 

 two thirds of its volume being nitrogen. The use of water-gas, result- 

 ing from the decomposition of steam in passing through a hot chamber 

 filled with coke, has been suggested, but this gas is also objectionable, 

 because it contains, besides hydrogen, the poisonous and inodorous 



TOL. XXII. 14 



