250 THE ADDRESSES, LECTURES, ETC., OF 



paper read before the Koyal Society of Edinburgh, that even with 

 perfect combustion a microscopic dust is sent up into the atmo- 

 sphere, each particle of which may form a molecule of fog. We 

 have evidence indeed, that the whole universe is filled with dust, 

 and this is, according to Professor Tyndall, a fortunate circum- 

 stance, for without dust we should not have a blue but a pitch 

 black sky, and on our earth we should be, according to Mr. Aitken, 

 without rain, and should have to live in a perpetual vapour bath. 

 The gas fires would contribute, it appears, to this invisible dust, 

 and we should, no doubt, continue to have fogs, but these would 

 be white fogs, which would not choke and blacken us. It seems, 

 moreover, reasonable to suppose, that perfect combustion cannot 

 contribute materially to the formation of even microscopic dust, 

 and that with the suppression of smoke our town atmosphere 

 would become as clear at any rate as that of Philadelphia and 

 other American cities where anthracite is the fuel used. 



Granted the cure of smoke, it might still be questioned whether 

 such a plan as here proposed could be carried out, on so large 

 a scale as to affect our atmosphere, with the existing mains and 

 other plant of the gasworks. If gas had to be depended upon 

 entirely for the production of the necessary heat, as is the case 

 with an ordinary gas and asbestos grate, it could easily be proved 

 that the existing gas mains would not go far to supply the 

 demand ; each grate would consume from 50 to 100 cubic feet 

 an hour, representing in each house a consumption exceeding 

 many times the supply to the gaslights. My experiments prove, 

 however, that an average consumption of from 6 to 8 cubic 

 feet of gas per hour, suffices to work a coke-gas grate, on the 

 plan here proposed. This is about the consumption of a large 

 Argand burner, and therefore within the limits of ordinary 

 supply. 



But independently of the practical question of supply it is 

 desirable on the score of economy to rely upon solid carbon 

 chiefly for the production of radiant heat for the following 

 reason : 



1000 cubic feet of ordinary illuminating gas weigh 34 Ibs., 

 and the heat developed in their combustion amounts to about 

 34 x 22,000 = 748,000 heat units. One pound of solid coke 

 develops in combustion, say, 13,400 heat units (assuming 8 per 



