March 4, 1898.] 



SCIENCE. 



305 



high efficiencies had been reported and ifc 

 had become important to ascertain what re- 

 lation the new sustained to the old system. 

 The machines employed in the research 

 were, in fact, the available combinations of 

 of the largest of the triple-expansion ' ex- 

 perimental engines ' of Sibley College, and 

 the combinations adopted were : 



1. The triple- expansion engine in its 

 usual condition. 



2. The intermediate- and the high-pres- 

 sure elements combined to make a com- 

 pound engine of usual proportions — three 

 to one. 



3. The low- and the high-pressure ele- 

 ments combined to produce a compound of 

 the peculiar sort above mentioned — -seven to 

 one. 



Earlier reports upon the performance of 

 engines of these several types had been made 

 to the same Association and the results so 

 reported had been as below ; the second of 

 the three cases illustrating the novel prac- 

 tice which it was here sought to study : 



several types of engine. Taking the best 

 performance of the ideal engine as varying 

 as the logarithm of the pressure employed, 

 as also found by experience to be approxi- 

 mately the fact with good engines, the gain 

 to be fairly anticipated by adopting the 

 higher pressure, other things being equal, 

 should be such as to give the figures 11.8, 

 12.84 and 11.16 pounds of feed-water per 

 horse-power per hour, for the three cases re- 

 spectively. The relative efficiency will then 

 be expressed by the figures 0.95, 0.87, 1.00. 

 The engine of usual type, as a compound, 

 when well-designed and built, thus gives a 

 performance within 5 per cent, that of the 

 best known triple-expansion engine ; the 

 compound, with exaggerated cylinder-ratio, 

 lacks 13 per cent, of the efficiency of the 

 triple-expansion and 7 per cent, that of the 

 standard type of compound. Leavitt's 

 Chestnut Hill engine, for which the figure 

 11.2 is reported, may be taken as identical 

 with the Reynolds pumping engine in rela- 

 tive efficiency ; correction being made for 



Cask op Compound vs. Triple and Intbbmediate Foems. 



Engine. 



Standard 

 Compound. 



Intermediate 

 Form. 



Triple 

 Expansion. 



Number of cylinders in series ... 



Steam-pressure, absolute 



"Vacuum, in. mercury 



Ratio of expansion 



Revolutions per minute 



Leng;th of stroke, ft 



Piston speed, per minute, ft 



Cylinder-ratio 



Drop between cylinders 



Dry steam, per I. H. P. per hr. 

 Difference favoring compound... 

 Difference in favor of triple 



St. cons, reduced to 175 lbs 



Comparative effio. on this basis 



2 

 151.6 



27.75 



20.40 



18.57 



10.0 



371.5 



4 



None 



12.156 

 0.684 lbs. = 5. 3 $! 

 0.478 lbs. = 4% 



2 



175.5 

 25.3 



33. (nom.) 

 76.4 

 4 

 611.2 

 7 

 14 lbs. 

 12.84 



1.16 lbs. =9% 



2 



135.5 

 27.6 

 19.55 

 20.31 

 5 



203 



1, 3, 7 

 None 

 11.678 



11.8 

 0.95 



12.84 

 0.87 



11.16 

 1.00 



The table contains, in the last two lines, 

 figures added to bring into more perfect 

 comparison the relative economy of the 



difference in pressures. Were correction 

 naade for differences in ratios of expan- 

 sion, the result above indicated would 



