120 PRELIMINARY REPORT ON COAL-TESTING PLANT, [bull. 261. 
GAS-PRODUCER PLANT. 
In considering the possible increase in efficienc}' of the boiler tests 
with a compound engine substituted for the simple engine used, the 
fact should not be overlooked that a corresponding increase in the 
efficiency of the gas-producer tests may be brought about under the 
most favorable conditions. The gas engine is passing through a tran- 
sitional period. In the larger sizes the vertical single-acting engine is 
being replaced by the horizontal double-acting. . Other changes and 
improvements are constantly being made which tend to do for the gaa 
engine what compounding and tripling the expansions have alreadJ 
done for the steam engine. 
The gas engine used in the trials recorded is a vertical three-cylinj 
der, single-acting engine with no means of changing the ignition whilJ 
the engine is running. A brief consideration of these points will lead 
at once to the conclusion that the gas engine and steam engine used in 
these tests compare very favorably, and that any increase in efficiencj 
in the boiler tests that might result from using a compound enginl 
can be offset b*» *Ub introduction of the more modern type of gal 
engine. 
