REVIEW OF FEED-WATER TESTS. 259 



feed-water being reduced from 27.8 Ibs. to 25.8 Ibs. Another 

 comparison may be made between test No. 7 and test No. 

 81 F. Here, with the same cut-off, an increase of pressure 

 from 80.5 Ibs. to 98.6 Ibs. was evidently the principal cause of 

 a reduction in the consumption from 29.03 Ibs. per I. H. P. per 

 hour to 25.31 Ibs. 



In the list of the compound engines, there are two tests 

 which can be compared for this purpose, those numbered 32 

 and 36. In No. 32, with a pressure of 94.8 Ibs., and the cut- 

 off in the high pressure cylinder .305, the feed-water consump- 

 tion is 16.28 Ibs. per I. H. P. per hour. In test No. 36, with 

 126.8 Ibs. pressure, and the cut-off at .295, or practically the 

 same as in the other case, the consumption is reduced to 

 14.05 Ibs. 



That an increased pressure in the same engine is advanta- 

 geous under some circumstances, is clearly shown by test 48 A 

 and 48 C. In the latter the pressure was 100.2 Ibs., and the 

 consumption of feed-water 15.08 Ibs., while in the former the 

 pressure was 125,9 Ibs., and with practically the same load, the 

 consumption was 14.12 Ibs. In this case the benefit due to 

 the increase of pressure was largely enhanced by the increased 

 expansion obtained, the cut-off in the H. P. cylinder dropping 

 from .432 to .294. 



III. EFFECT OF SPEED UPON ECONOMY. 



The speeds, expressed in revolutions per minute, vary in 

 these tests from a minimum of 21 to a maximum of 356.7. 

 With such a wide range, there is reason for expecting informa- 

 tion as to the economy to be derived from increasing the 

 rotative speed, but the tests furnish no conclusive evidence on 

 this subject. The high-speed engines are all, or nearly all, of a 

 different class from the low-speed ones, and the nature of the 

 design and construction is such that certain features which are 

 necessary for the highest economy are sacrificed in order to 

 obtain the desired increase of speed. Many of the high-speed 

 engines have a single valve which performs all the functions of 

 the four valves in a slow-speed engine. The result is that 



