Sept. 2i, 1888.] 



SCIENTIFIC NEWS. 



307 



a ground space of only 9 ft. by 10 ft. I have always 

 taken the view, and it has been confirmed by practice 

 in many places, that when the consumption of gas is 

 regular there is no need for a large holder, provided the 

 generator is well able to make gas at the maximum rate 

 of consumption. In the case of engines, for instance, the 

 gas plant is to the gas-engine what the boiler is to the 

 steam-engine, and it is no more necessary to have a large 

 reserve of gas than to have a large reserve of steam. 



As regards the composition of the gas, it necessarily 

 depends somewhat on the quality of the coal used, 

 and on the fuel column being kept deep enough to 

 insure a reduction of the carbonic acid. It has been 

 analysed independently by Professor Wm. Foster and 

 others, and, roundly speaking, the gas now made has the 



to use only four volumes of the generator gas. On this 

 point, therefore, theory and practice are now fairly in 

 accord. By calculation the calorific power of 100 litres 

 of an average sample of the generator gas is 143,213 units 

 of heat, while that of 100 litres of ordinary 16 candle- 

 power lighting gas is 569,264 units. Tests made with a 

 calorimeter and in other ways confirm these figures 

 approximately. 



In 1881 only one engine of 3! h.p. had been worked 

 with this gas, and this showed a consumption of 1-46 lb. 

 of coal converted into gas per indicated h.p. per hour. 

 Since then a large number of engines have been worked 

 with it, one indicating over 80 h.p., and many inde- 

 pendent tests have been made. Details of these will be 

 found in a paper of mine in the Proceedings of the 



Figs, i and 2. — The Dowson Compact Plant for Making Generator Gas on a Moderate Scale. 



Steam producer and superheater ; b. Injector ; c. Gas generator ; d. Chimney and waste pipe ; e. Down pipe conveying gas to hydraulic 

 box ; f. Hydraulic box ; g. Inlet pipe of gas-holder ; h. Wet scrubber ; ii. Water spray pipes ; j. Water supply pipe ; k. Dry scrubber; 

 /. Gasholder ; m. Outlet pipe of gasholder ; «. Steam and air escape valve. 



same composition as that made some years ago. I then 

 thought that possibly in a large generator containing a 

 great mass of fuel at a high temperature the percentage of 

 hydrogen might be increased and that of the carbonic acid 

 reduced. Trials since made have, however, shown that 

 the average composition is much the same whether the 

 gas be made at the rate of 1,000 c. ft. per hour in a small 

 generator ->r at the rate of 15,000 c. ft. per hour in a 

 large one. ' in 1881 I stated that for gas engines it was 

 then necessary to use five volumes of the generator 

 gas for one of ordinary lighting gas, to develop the same 

 power. Theoretically, the comparative explosive force of 

 the two gases is as 3-8 ; 1, and it was evident that so 

 long as practice required five to one, the weaker gas was 

 not being used to the best advantage. Since then some 

 important modifications have been niade in the Otto 

 engines, and I am glad to say that it is now necessary 



Institution of Civil Engineers for last year, and on the 

 present occasion it will be sufficient to give a few in- 

 stances only. For more than four years Messrs. Cross- 

 ley Brothers, the English makers of the Otto engines, 

 have used this gas exclusively at their works for an 

 average of about 150 h.p., and after a careful trial 

 extending over thirty-five weeks they found that the fuel 

 consumption averaged only 1*3 lb. per indicated h.p. 

 per hour, including all waste, and the coal burnt in the 

 generator every night and during Sunday (=112 hours 

 per week) when the fire was alight, although there was 

 no work. At the time of this trial the construction of 

 the generator rendered it necessary to draw the fire 

 every two or three weeks, to remove the clinker adher- 

 ing to the firebrick lining. Since then I have altered the 

 generator, so that when the fire has once been lighted it 

 need never be drawn ; one of these generators has now 



