Apkil 9, 1897.] 



SCIENCE. 



575 



tively 2.344, 3.969, 6.977 and 10.266 inclies; 

 the stroke of piston being 4.5 inches, and 

 its speed of revolution usually about 300 

 per minute. The engine possesses a num- 

 ber of interesting and ingenious new de- 

 vices introduced by its designers and 

 builders, Messrs. Hall and Treat, graduate 

 students of the College; and its boiler, a 

 water-tube construction, is also original in 

 plan. 



The trials of this engine, conducted under 

 many difiBculties, and often afc some hazard, 

 in consequence of perpetual trouble met 

 with, in the early part of its history, in se- 

 curing a reliable means of feeding against 

 the high boiler-pressure, and in finding a 

 good method of obtaining water-level indi- 

 cations, resulted in showing an exceedingly 

 low steam and heat consumption. After a 

 good feed pump had been secured, and the 

 boiler could be handled with safety and 

 without anxiety, and after the constructors 

 had devised a new and reliable system of 

 water-level indication, trials were carried 

 on, the outcome of which has now been 

 published. The net result was the indica- 

 tion of a pressure of maximum efficiency, 

 for this engine, less than that for which it 

 was designed, and the obtaining, at best ad- 

 justments, of an efficiency of about thirty 

 per cent., a steam consumption of about ten 

 pounds per I. H. P. per hour, and of 226 

 B. T. U. per I. H. P. per minute, 13,560 per 

 hour, at 300 and 400 pounds pressure. The 

 engine was provided with 'reheaters,' or 

 drying chambers, between each pair of 

 cylinders, and, these being thrown out and 

 the steam worked wet, the consumption 

 rose to from 13.7 pounds at 500 pounds 

 pressure to 15.5 at 300 pounds, per I. H. P. 

 per hour. The wastes in the latter case 

 were substantially the same at high as at 

 low pressures, and the deduction follows 

 that we may expect at high steam pressures 

 about as close an approximation to the 

 ideal thermodynamic case as at ordinary 



tensions of steam. There still remains, 

 however, some question as to the exact 

 eificiency of even this engine; owing to irreg- 

 ularity and shortness of most of the trials, 

 due to the difficulties with the boiler above 

 mentioned, and some uncertainty regard- 

 ing leakage past piston and valves ; the ex- 

 istence of which is at least indicated by the 

 measurements of the indicator diagrams. 



A comparison of these figures with those 

 of larger engines in commercial use can 

 only be made after allowing for the com- 

 paratively large internal wastes, due to the 

 excessive proportion of area of cylinder wall 

 to weight of steam passing through the 

 engine, in the case of small machines. 

 Eeducing these wastes by any probable 

 fraction, the heat, steam and fuel con- 

 sumption of the engine at its regular pres- 

 sure, above thirty- three atmospheres, would 

 give a consumption of not far from 7J 

 pounds of steam per I. H. P. per hour, or 

 from 7,500 to 8,000 B. T. TJ., according to 

 temperature of feed water. 



The diagram herewith presented shows 

 the relation of the efficiency of the ideal, 

 purely thermodynamic, engine of similar 

 cj'cle — the Eankine form — to the actual 

 performance. The curve A is that of the 

 best ideal, case B that of the average best 

 performance of the experimental engine, C 

 that with its reheaters out of use, and the 

 various observations indicated on the chart 

 show the variations due to varying effi- 

 ciency of reheating and to other variable 

 conditions of operation. D may be taken 

 as representing fair average performance, 

 and E the limit of best work ; while F is 

 not far from what should be expected from 

 large engines of similar type, and is taken 

 as representative of the commercial attain- 

 able performance of such good practice at 

 500 pounds pressure and under. 



These curves of relation of steam used to 

 power produced are of the form 

 w = a / log p ; 



