2io THE POPULAR SCIENCE MONTHLY. 



gas, carbonic oxide, the introduction of which into dwelling-houses 

 could not be effected without considerable danger. A more satisfac- 

 tory mode of supplying heating separately from illuminating-gas would 

 consist in connecting the retort at different periods of the distillation 

 with two separate systems of mains for the delivery of the respective 

 gases. Experiments made some years ago by Mr. Ellisen, of the Paris 

 gas-works, have shown that the gases rich in carbon, such as defiant 

 and acetylene, are developed chiefly during an interval of time, begin- 

 ning half an hour after the commencement and terminating at half the 

 whole period of distillation, while during the remainder of the time, 

 marsh gas and hydrogen are chiefly developed, which, while possessing 

 little illuminating power, are most advantageous for heating purposes. 

 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 may 

 be shortened from six hours, the usual period in former years, to four, 

 or even three hours, as now practiced at Glasgow and elsewhere. By 

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

 tion to the former quantity of illuminating-gas of superior quality, a 

 similar quantity of heating-gas, resulting in a diminished cost of pro- 

 duction and an increased supply of the valuable by-products previously 

 referred to. The quantity of both ammonia and heating-gas may be 

 further increased by the simple expedient of passing a streamlet of 

 steam through the heated retorts toward the end of each operation, 

 whereby the ammonia and hydrocarbons still occluded in the heated 

 coke will be evolved, and the volume of heating-gas produced be aug- 

 mented by the products of decomposition of the steam itself. It has 

 been shown that gas may be used advantageously for domestic pur- 

 poses with judicious management even under present conditions, and 

 it is easy to conceive that its consumption for heating would soon in- 

 crease, perhaps tenfold, if supplied separately at say one shilling a thou- 

 sand cubic feet. At this price gas would be not only the cleanest and 

 most convenient, but also the cheapest form of fuel, and the enormous 

 increase of consumption, the superior quality of the illuminating-gas 

 obtained by selection, and the proportionate increase of by-products, 

 would amply compensate the gas company or corporation for the com- 

 paratively low price of the heating-gas. 



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

 cumstance that a pound of gas yields in combustion twenty-two thou- 

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

 of a pound of ordinary coal. This extra heating power 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 



