ON FUEL ECONOMY. 107 



ovens, without steaming the charge, usually varies between the following 

 limits, approximately: — 



COa CO CnHm CH^ H^ Na 



45 to 55, 5 to 10 per cent. 



50-0 7-0 



The calorific value of a gas of the mean composition indicated would be 

 about 560 gross and 495 net B.Th.Us. per cubic foot at 00° Fahr. and 

 30 in. barometer. The con-esponding values for a ' debenzolised ' coke- 

 oven gas, containing only 25 per cent, of methane, would be about 485 

 gross and 425 net. And inasmuch as the thei-mal efficiency of such 

 carbonisation processes is admittedly high,^ there would appear to be no 

 particular reason, on the ground merely of thermal efficiency, for seek- 

 ing to supersede the 1913 practice. The plea for the change is presum- 

 ably based on the desire, on the part of gas undertakings, to convert a 

 substantial part (or possibly the whole) of the coke into water gas, and 

 thus to increase the gas-make per ton of coal at a corresponding 

 sacrifice of the coke-yield. 



(7) Water gas may be generated from coke with a thermal efficiency 

 of (up to) 70 per cent. ; it contains on an average: — 



CO2 CO H2 CH4 Na 



4-5 430 480 05 4-0 per cent. 



Its calorific values per cubic foot at G0° Fahr. and 30 in. barometer 

 are approximately 300 B.Th.Us. gross, and 275 net, or rather more 

 than half those of the ' straight ' coal gas already referred to. Its 

 calorific intensity, however, is distinctly higher, but its range of 

 inflammability with air considerably wider, than that of coal gas. Its 

 high carbonic oxide content makes it a poisonous gas, and, owing to 

 its high hydrogen and low methane contents, its mixtures with air are 

 very liable to back-fire. For these reasons it is not a desirable gas for 

 domestic uses unless largely diluted ; and any large admixture of it 

 with coal gas in public supplies would undoubtedly add materially to 

 the dangers of carbonic oxide poisoning and of gas explosions in houses. 

 (S) With regard to the question of the dangers of carbonic oxide 

 poisoning with a gas containing a, large proportion of water gas, it 

 may be recalled that twenty years ago this was the subject of an official 

 Inquiry by a Committee appointed by the Home Office, of which Dr. 

 J. S. Haldane and the late Sir William Eamsay were members. They 

 had laid before them detailed infonnation as to the Uses of Water Gas 

 in the United States and its effect upon Human Health. In their 

 Report (C. 9164 of 1899) they stated: — 



' The most direct, and in our opinion, the only effective method 

 of preventing danger from water gas is to fix a limit which 

 the carbonic oxide in a public and domestic gas supply 



" It has recently been shewn that the two Metropolitan Gas Companies in the year 

 1013 actually sent out in the form of gas, coke, and tar, rather more than 70 per cent. 

 of the potential energy of the coal carbonised, and that over-all efficiencies exceeding" 

 82 per cent, have been attained in large-scale carbonising tests. 



