26 



Dr. E. FranJcland 



[Feb. 10, 



The fog once formed is rendered more persistent by tlie coating 

 of tarry matter wbich it receives from the products of the imperfect 

 combustion of smoky coal. The speaker had made numerous 

 experiments on the retardation of evaporation by films of coal tar. 

 He had found that the evaporation of water in a platinum dish 

 placed in a strong draught of air was retarded in one experiment by 

 84 per cent, and in another by 78*6 per cent., when a thin film of 

 coal tar was placed on the surfaces. Even by the mere blowing of 

 coal smoke on the surface of the water for a few seconds, the 

 evaporation was retarded by from 77*3 to 81*5 per cent. Drops of 

 water suspended in loops of j)latinum wire were also found to have 

 their evaporation retarded by coal smoke. Hence arise the so-called 

 dry fogs which have been observed by Mr. Glaisher in balloon ascents, 

 some examples of which are given in the following table : — 



Foa IN COMPARATIVELY DrY AiR. 



Place of Ascent. 



Altitude. 



Wolverhampton . . 

 Crystal Palace . . 



>» 



Woivertou 

 Woolwich 



5» 



foot. 

 5,922 

 3,698 

 9,000 

 1,000 

 11,000 

 6,000 

 4,400 



Temperature 

 of Air. 



° F. 

 53-5 

 385 

 32-5 

 64-7 

 30-0 

 44-0 

 42-0 



Degree 

 of Huuiidity. 



100 =: Saturation. 

 61 

 62 

 52 

 53 

 68 

 64 

 52 



Thus the smoke of our domestic fires constitutes a potent cause 

 both for the generation and the persistency of town fogs. In London, 

 at all events, if all manufacturing oj^erations were absolutely to 

 cease, the fogs would not be perceptibly less dense or irritating. 

 Granting then this cause of town fogs, what are the remedies open 

 to us ? The speaker was of opinion that the substitution of a suffi- 

 cient number of smoke-consuming grates (assuming a smoke-con- 

 suming grate to have been invented), for the 1,800,000 fire-places of 

 London was quite hopeless, and that one remedy only could be 

 of any appreciable service — tlie importation of bituminous coal must he 

 forhidden. This is a case in which individual efi'ort can do nothing ; 

 but State or municipal action would be simple and decisive. 



There need be no fear that the price of smokeless fuel would rise 

 inordinately, for the sources of this fuel are too numerous and inex- 

 haustible to admit of either a monopoly or a serious rise in price. In 

 addition to the enormous stores of smokeless coal in the Welsh coal- 

 fields, every bituminous coal yields a smokeless coke, either in the 

 retorts of gasworks or in coke ovens. On the average, 100 tons of 

 smoky coal yield 60 tons of coke, the remaining 40 tons being 

 driven off as combustible'^'gas, ammoniacal liquor and tar ; and as 

 there is an almost unlimited demand for these products, it is not 



