No. 6.] president's address b. a. a. s. 353 



and more economicaly, without allowing any of the fuel employed 

 to reach the atmosphere unburnt. This most desirable result 

 may be effected b3^ 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 

 distillation 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, resulting from the decomposition of steam 

 in passing through a hot chamber filled with coke, has been sug- 

 gested, but this gas also is objectionable, because it contains, 

 besides hydrogen, the poisooous and inodorous gas carbonic 

 oxide, the introduction of which into dwelling-houses could not 

 be effected without considerable danger. A more satisfactory 

 mode of supplying heating separately from illuminating gas 

 would consist in connecting the retort at different periods of the 

 distillation with two separate S}'stems of mains for the delivery 

 of the respective gases. By resorting to improved means of 

 heating the retorts with gaseous fuel, such as have been in use at 

 the Paris gas-works for a considerable number of years, the length 

 of time for effecting each distillation mav be shortened from six 

 hours, the usual period in former years, to four, or even three 

 hours, as now practised at Glasgow and elsewhere. By this 

 means a given number of retorts can be made to produce, in ad- 

 dition to the former quantity of illuminating gas of superior 

 quality, a similar quantity of heating gas, resulting in a dimi- 

 nished cost of production, and an increased supply of the valuable 

 by-products previously referred to. 



The greater efficiency of gas as a fuel results chiefly from the 

 circumstance that a pound of gas yields in combustion 22,000 

 heat units, or exactly double the heat produced in the combustion 

 of a pound of ordinary coal. This extra heating pow'er is due 

 partly to the freedom of the gas from earthy constituents, but 

 chiefly to the heat imparted to it in effecting its distillation^ 

 Recent experiments with gas burners have shown that in this 

 direction also there is much room for improvement. 



The amount of light given out by a gas flame depends upon 

 the temperature to which the particles of solid carbon in the 

 flame are raised, and Dr. Tyndall has shown that of the 

 radiant energy set up in such a flame, only the l-25th part 

 Vol. X. w 2 No. 6. 



