60 



SCIENCE. 



[N. S. Vol. XVII. No. 419 



small gas producer. These generators are 

 very simple in operation and furnish a 

 convenient and economical means of ob- 

 taining power at a much lower rate than 

 with the ordinary city lighting gas. Gen- 

 erally small anthracite coal or coke is used, 

 but several methods employ bituminous 

 coal, lignites or wood. With bituminous 

 coal, means must be provided for removing 

 the tar and ammonia and other products 

 of distillation. 



The process of generation in some of the 

 more recent producers is entirely auto- 

 matic and depends upon the demand of 

 the engine, so that no storage capacity is 

 required. The economy of these small 

 producers is shown by tests which give 

 one horse-power on a 16-horse-power en- 

 gine with a consumption of only 1.1 pound 

 of fuel. For engines above forty horse- 

 power one horse-power can be obtained on 

 seven eighths pound of fuel. 



The gas-engine industry received a signal 

 impetus when it was discovered that blast 

 furnace gases could be readily utilized di- 

 rect in combustion engines without, the 

 intervention of boilers and without any 

 special purifying processes. A still more 

 important circumstance which is far reach- 

 ing in its results is the fact shown by Pro- 

 fessor Hubert, of the Liege School of 

 Mines, that the superior economy of the 

 gas-engine enables equal power to be ob- 

 tained with 20 per cent, less consumption 

 of furnace gas than was formerly used in 

 the generation of steam. 



The successful employment of large com- 

 bustion engines in this way utilizes vast 

 sources of power which a few years ago 

 were allowed to go to waste or at most were 

 used very inefficiently. 



The high thermal efficiency of the gas- 

 engine has long been recognized and the 

 possibility of further development is a 

 promising factor in this field. The already 



accomplished efficiency of 38 per cent, re- 

 ported by Professor Meyer, of Gottingen, 

 greatly exceeds the maximum theoretical 

 efficiency of the steam-engine and more 

 than doubles its actual best obtainable 

 working efficiency, but the end is not yet. 



With higher compression even greater 

 efficiencies may be expected. But with 

 high compression there is danger of pre- 

 mature explosion, due to the generation of 

 heat in compressing the gas in the presence 

 of oxygen ; for this reason Herr Diesel ■ 

 compresses the air separately. Under a 

 pressure of 500 pounds or more, which is 

 used in the Diesel motors, the air becomes 

 very hot and readily ignites a charge of 

 liquid fuel which is injected into the com- 

 pression chamber. There is no explosion; 

 combustion occurs while expansion goes 

 on and the heat generated disappears in the 

 form of work. 



Efficiencies of 30 per cent, or more have 

 been obtained with blast furnace gases 

 which contain a very small percentage of 

 hydrogen, and this with the high rates of 

 compression which can be carried has led 

 to the advocacy of non-hydrogenous mix- 

 tures in large engines. Certainly very 

 high rates of compression may be had with 

 a non-hydrogenous producer gas without 

 fear of premature ignition, and it has the 

 additional advantage of economical pro- 

 duction. 



The practice of making the cylinder in 

 combustion engines act alternately, first as 

 air compressor then as motor, has the ad- 

 vantage of greater simplicity, but it means 

 immensely larger engines for the same 

 power, since the number of effective im- 

 pulses is thus cut in two. 



The danger of pre-ignition and conse- 

 quent severe shock on the engine also 

 necessitates very heavy construction in the 

 smaller engines in order to obtain a rea- 

 sonable degree of safety in operation. 



