APPLIED MECHANICS LECORNU. 273 



fed \vith poor coal or coke. Results may thus be obtained not exceed- 

 ing 400 grams of coal per effective horespower. For realizing the 

 importance of tliis result, it is sufhcient to recall that with a compound 

 steam engine and coal with 10 per cent ash, capable of giving 7,200 

 calories per kilogram the consumption exceeds 600 grams and often 

 reaches 1 Idlogram. 



It is desirable to be able to feed the gas producer with any kind of 

 coal whatever. The employment of greasy coals is rendered cUfii- 

 cult by the formation of tars wliich, when the combustion is not com- 

 plete, tend to obstruct the chstributing system. Further, greasy car- 

 bon, in order to feed regularly, requires constant stoking which in turn 

 disturbs the working of the motor. Letombe succeeded in over- 

 coming these difficulties. He observed that, in order to keep the coal 

 feeding properly in the gas producer, it was only necessary to start the 

 combustion of the volatile product at the very moment of its distilla- 

 tion. His gas producer is overfed, having at its upper part a stepped 

 grate by which the air necessary for the combustion is introduced. 



The greasy coals are in general too costly for the production of cheap 

 gas. It would be better to use those combustibles of copious ash 

 wliich can not be employed in other ways. The principal cUfficulty 

 then is to overcome the resistance offered to the flow of the air. 

 Kerpley made for that purpose a liigh-prcssure gas producer (400 to 

 700 miUimeters of water) the rotating grating of which is perforated 

 with a great number of holes distributed over itc whole surface. 



There has just been put into service at the German steel works at 

 Bruckhausen, a blower driven by probably the most poAverful gas 

 engine in existence. Tliis engine is a four-cycle motor, with two 

 cyHnders in tandem and of 1.40 meters stroke. The (Uameter of the 

 gas cyhnders is 1.20 meters, of the vent cylinders, 1.90 meters. 



For a long time gas engines were worked by valves. Such engines 

 are now in competition with those using cyhndrical sUdes or cocks. 

 The great speeds accentuated the well-known faults of the valves due 

 to the noisy shocks, tlie hammering, the difficult}^ of adjustment, the 

 stratification of the gas, etc. The Mercedes and Ilonault motors use 

 turning cocks. The Knight motor, wliich has attained such success 

 since its appearance, uses a distribution made by two concentric 

 sheaths placed within the interior of the cyhnder and worked by 

 eccentrics. The stratification is smaU because of the care taken in 

 giving the parts the necessary dimensions. Fear might be enter- 

 tained over difficulties in lubricating and chiUing. But experience 

 shows that these difficulties are easily overcome. Oil, constantly 

 renovated, does not lose its fluidity. The doing away with the valves 

 allows a very sim.ple shape for the explosion chamber, the surface of 

 wliicli may thus be very much reduced, and to this Knight attributes 

 the great flexibility of his motor. The reduction of surface exposed 



