Decembee 2, 1898.] 



SCIENCE. 



767 



a purely thermodynamic case. At the boiler, 

 also, there are no losses by conduction or 

 radiation and the flue-gases are reduced to 

 the temperature of the steam in the boiler 

 before discharge. 



Of the total heat developed in the furnace, 

 now only 104,200 B. T. U., the large propor- 

 tion, 31,400, are still wasted by way of the 

 chimney, since the gases must be sent out 

 at least as hot as the boiler-steam. The 

 quantity sent to the engine is 72,800, to 

 which is added the saved heat from the 

 economizer, here also assumed to be em- 

 ployed, 28,100 B. T. U. The engine re- 

 ceives, thus, a total of 100,900 B. T. U. per 

 minute, of which 5,600 is returned by way 

 of the feed-pipe, giving a net supply of 

 93,300 for the thermodynamic cycle. This 

 amounts to 148 B. T. U. per I. H. P. per 

 minute, equivalent to anefiBciency of 0.286. 

 The ideal thus demands but 0.67, two- thirds 

 the heat-supply of the actual engine. 



This graphical analysis has special in- 

 terest in connection with the employment 

 of the engine-trial data in the calorimetric 

 analysis of Hirn for detection and measure- 

 ment of thermodynamic and other defects 

 of the actual engine cycle. Where the 

 jacket is employed, it is to be understood 

 that the process of the flow of heat from the 

 jacket-steam into the wall of the engine- 

 cylinder is a continuous and uniform opera- 

 tion ; but that the method and rate of flow 

 from metal to steam, within the cylinder, is 

 irregular and its precise law unknown. 



The work of the Committee results in the 

 recommendation that the thermal econom- 

 ical value of steam-engines should be stated 

 in thermal units per indicated horse-power. 

 It takes the so-called Eankine standard 

 cycle — a thermodynamic cycle with iso- 

 thermals as upper and lower limiting bound- 

 aries and with complete adibatic expansion 

 and without clearance of compression— as 

 the standard of comparison, the unit of 

 thermodynamic efficiency with which to ' 



compare the efficiency of the real engine, 

 and describes the method of testing and 

 recording results of test and the forms of 

 computation required in affecting this com- 

 parison of the ideal with the real case. 



The ideal, Rankine, cycle was first pro- 

 posed by that writer in 1854 in a paper 

 published in Transactions Royal Society of 

 Edinburgh, as of date of January 19, 1854. 

 The paper was reproduced in the ' Miscel- 

 laneous Papers of Rankine,' page 400, sec- 

 tion 46. Clausius described the same cycle 

 in Poggendorif 's Annalen, 1856, and later 

 in his ' Mechanical Theory of Heat,' quite 

 independently, however, of Rankine, of 

 whose work he was at the time unaware.* 



The following are the summarized recom- 

 mendations of this committee, and it is rec- 

 ommended by them that authors presenting 

 papers to the British Institution of Civil 

 Engineers be invited to conform to these 

 suggestions: 



(1) That 'thermal efficiency' as ap- 

 plied to any heat-engine should mean the 

 ratio between the heat utilized as work on 

 the piston by that engine and the heat sup- 

 plied to it. 



(2) That the heat utilized be obtained 

 by measuring the indicator diagrams in the 

 usual way. 



(3) That in the case of a steam-engine 

 the heat supplied be calculated as the total 

 heat of the steam entering the engine less 

 the water-heat of the same weight of water 

 at the temperature of the engine exhaust, 

 both quantities being reckoned from 32° F. 



(4) That the temperature and pressure 

 limits, both for saturated and heated steam, 

 be as follows : 



Upper limit: the temperature and pres- 

 sure close to, but on the boiler side of the 

 engine stop-valve, except for the purpose of 

 caculating the standard of comparison in 



* Hirst's Translation of Clausius, 1867, page 161. 

 This note, however, does not appear in the German 

 edition of 1876. 



