574 



SCIENCE. 



[N. S. Vol. V. No. 119. 



tested up to 1,350 pounds and operated, 

 with the engine, at times, at above 600 

 pounds pressure. But even these working 

 pressures are comparatively low figures be- 

 side those of Perkins, who sixty years ago 

 operated steam engines at 1,000 and 1,500 

 pounds and upward, and whose disciple, 

 Dr. Albans, built a number of engines for 

 regular work at nearly as great tensions of 

 steam. Owing to their incomplete expan- 

 sion, and owing to the fact that they were 

 not compounded or otherwise insured 

 against great ' cylinder condensation,' the 

 engines of neither of these experimentalists 

 attained what would be to-day thought re- 

 markable economy. It was, however, re- 

 markable for their time. 



In those early days a piston speed of ' 128 

 times the cube root of stroke ' was standard 

 practice ; the figure has now risen to, in some 

 instances, four times this figure, and 

 standard practice ranges from 600 feet, 

 with small 'automatics,' to 1,000 feet 

 per minute in large engines. The size, 

 weight and cost of the machine for any 

 stated power have been correspondingly 

 diminished. The main source of gain in 

 the meantime has been the diminution of 

 the internal thermal wastes of the machine, 

 which constituted in the days of Watt 

 ninety per cent, or more of the demand 

 for steam in the old Newcomen engine 

 which he reconstructed, thirty to forty 

 per cent, of the steam consumption in his 

 own engines, and which has now fallen in 

 the best contemporary machines to about 

 twenty per cent., still constituting an im- 

 portant source of loss. ' Duty ' has risen 

 from about 10,000,000 foot-pounds in the 

 first of these series to 60,000,000 in the 

 second, and has attained to-day about 

 150,000,000 and promises to become 160,- 

 000,000 at the end of the century, per 

 hundred pounds of best coal consumed. 

 Reduced to steam consumed, the latter 

 figures correspond to about eleven and a-half 



and about eleven pounds per horse-power 

 per hour, and, in heat expended, about as 

 many thousand B. T. U., with high tem- 

 perature feed-water with large proportion, or 

 ten per cent, more with moderate admixture, 

 of jacket water. In fuel, it corresponds to 

 from IJ to If pounds per I. H. P. per hour. 

 The average steam engine of even good 

 makers seldom attains much more than 

 one-half the efi&ciency of the modern record- 

 making machines. 



The triple-expansion engine of Sibley 

 College, built and employed as an experi- 

 mental engine purely, illustrates the action 

 of good engines at about 125 pounds pres- 

 sure (absolute). It gives the indicated 

 horse power on about 13.3 pounds of steam, 

 15.1 per D. H. P., and 14,160 B. T. U. per 

 hour ; its total ratio of expansion being 

 13.83, and the jackets supplying 13.72 per 

 cent, of the feed water. The thermody- 

 namic efficiency of the corresponding Carnot 

 Cycle would be 24.7 per cent.; that of the 

 engine is 18 per cent. A low vacuum, 22 

 inches, makes this work still more remark- 

 able for so small an engine. It operated 

 at 140 I. H. P. in this case. The ma- 

 chine was built for 175 pounds steam — 

 another disadvantage. The dictum of 

 Dwelshauver-Dery and the writer, that the 

 jackets produce best efi'ect, and efficiency 

 attains a maximum, when the expanding 

 steam is dry at or before final exhaust into 

 the condense]', is confirmed by these re- 

 sults. The jackets are in this engine always 

 advantageous. 



The records first given, as the present 

 maxima, are from large engines operated at 

 from 125 to 175 pounds pressure. Those are 

 triple-expansion. The following are data 

 relating to the quadruple-expansion experi- 

 mental engine of Sibley College, Cornell 

 University, operated at, in some cases, 500 

 pounds pressure and upward. The ma- 

 chine is of but twenty horse-power rating; 

 its cylinders having diameters of respec- 



