64 PROCEEDINGS OF SECTION B. 



purposes comes first in importance, both on the score of its world- 

 wide application and the amount of money involved. The capital 

 invested in public gas-light companies in Great Britain alone 

 exceeds 130 million pounds sterling, while the amount of coal 

 consumed annually for gas-making purposes in the same country 

 is not less than fifteen million tons. The cost of producing gas is 

 now much less than formerly. By employing gas-fired furnaces 

 and sloping retorts the working charges of handhng and carbonising 

 coal have been reduced as low as l|d per ton. The practically 

 universal introduction of incandescent mantles for illumination and 

 of gas stoves for cooking has relegated the illuminating power of 

 the gas to a position of smaller importance, and the efforts of gas 

 engineers are being more and more directed towards increasing 

 the calorific value. 



Before leaving the subject of gas for illuminating purposes; 

 mention should be made of the extensive use of acetylene and the 

 so-called air-gas for small installations where coal-gas would be 

 both expensive and troublesome. In the United States it is 

 interesting to note that many gas-light companies retort no coal 

 but manufacture carburetted water-gas. The latter is much 

 cheaper than coal-gas, but its use would not be permitted in 

 England owing to the high percentage of carbonic oxide which 

 it contains. 



After illumination, the next most important use for gas is for 

 power and heating purposes. The history of gas engines is 

 interesting. Patents for various forms of machines working with 

 gas were taken out over and over again during the last hundred 

 and twenty years, but it was only after the introduction of the 

 Otto engine, some thirty years ago, that gas engines became 

 commercially successful. At the present day they are numbered 

 by thousands, the English firm of Crossley Bros, having alone 

 manufactured over 70,000 engines. 



Owing to convenience of supply coal-gas is frequently em- 

 ployed for small plants, but the cheapest and most generally used 

 source of power is producer gas, made by passing air and steam 

 alternately through incandescent coal or coke contained in vessels 

 called " producers." The gas, which consists mainly of carbonic 

 oxide, hydrogen and nitrogen, passes on its way to the engine 

 through a scrubber which removes dust and tarry matters. 



In the Mond producer, which has been specially designed to 

 deal with bituminous coal and low-grade fuels, such as peat, and 

 also to collect as much as possible of the nitrogen of the fuel in the 

 form of ammonia, a very large quantity of steam is used. Mond 

 gas contains 80-85 per cent, of the total heat energy of the fuel, 

 while at the same time in its manufacture an amount of sulphate 

 of ammonia is produced which may, even with low grades of fuel, 

 be worth as much as the fuel itself. The calorific value of the 

 gas is about 150 b.t.u. per c. ft. as made from slack, and conse- 

 quently by using Mond gas and gas engines at least double the 



