^54 



SCIENCE, 



[N. S. Vol. IX. No. 230. 



«tate of instability as to quality. The investi- 

 gations of the ' theorie generique ' made by Kan- 

 kine, Clausius, Zeuner and others resulted in 

 establishment of no rational expressions for the 

 actual heat-exchanges of the real, as distin- 

 guished from the ideal, engine, and Hirn's 

 ' theorie experimentale,' as developed by that 

 great investigator and his disciples, is still the 

 only resort of the student of the curious extra- 

 thermodynamic processes accompanying the 

 thermodynamic operation of the engine. 



Superheating has come to be looked upon, 

 mot as method of giving superior thermody- 

 namic action, but as simply a provision for reduc- 

 ing internal wastes due to heat- exchanges be- 

 tween the steam and the metal surrounding it. 

 Its effectiveness was recognized as early as 

 Trevethick's time (1828 or earlier) and became 

 well understood about the middle of the cen- 

 tury ; since which time numerous inventions 

 have been made, looking to its utilization, few 

 giving any promise of success. The Alsatian 

 school has revealed very completely the method 

 and the effect of its adoption, and it has come to 

 be well understood that its province is simply 

 to reduce that form of waste known as ' initial 

 condensation' or 'cylinder condensation.' Its 

 successful use would effect the suppression of 

 those losses in such manner, in the words of 

 DwelshauversDery, as to give maximum effi- 

 ciency by securing the exhaust of the steam 

 from the engine in the dry and saturated condi- 

 tion. This is, in his opinion, the practical 

 criterion of most perfect action. The actual 

 gain has been found by Hiru to be, in several 

 cases studied by him experimentally, from 20 

 to nearly .50 per cent., with a superheat amount- 

 ing to from 210°C. to 245°C. The nearest ap- 

 proximation yet reported to the ideal, purely 

 thermodynamic, case has been effected by this 

 means — particularly, of late, by Schmidt. 



The failures of the past have been due to 

 difficulties in securing an apparatus which can- 

 not be rapidly injured by excess of heat in 

 presence of superheated vapor of water, and a 

 system of lubrication of the cylinder and piston 

 capable of working satisfactorily at the tem- 

 peratures attained in effective superheating. 

 The latter obstacle is now overcome, largely, by 

 the use of the high-test mineral oils ; the former 



remains a serious obstruction. The increasing 

 steam-pressures of our day also reduce both the 

 need and the availability of increasing super- 

 heat. 



The results of successful superheating exhibit 

 themselves both at the engine and at the boiler, 

 and, as with multiple-cylinder engines, the gain 

 at the boiler in economical employment of fuel 

 is greater than that at the engine through a more 

 perfect thermodynamic action ; for the reduc- 

 tion of the demand for steam at the engine re- 

 sults in an increased economy in the produc- 

 tion of such steam through the larger propor- 

 tion of heating surface to weight of steam 

 produced. Thus a gain of 20 per cent, at the 

 engine may be accompanied by a gain of 22 per 

 cent, or more in fuel as measured at the boiler. 

 The desirable amount of superheat is that which 

 will prevent the condensation of the vapor en- 

 tering the steam-cylinder and insure its rejection 

 as saturated vapor at exhaust. 



The apparatus employed by various inventors 

 and investigators in this field, from 18.50 to our 

 own time is described at considerable length by 

 M. Sinigaglia, and the results of experiment are 

 recited. In many instances, recently, particu- 

 larly, it is reported that no serious inconven- 

 iences were met with in the application of this 

 system ; in other cases much trouble and some- 

 times serious accidents resulted, due to the 

 'burning' of the apparatus and its yielding, 

 thus weakened, to the pressure. Messrs. Lud- 

 wig and Weber obtained, in an extensive series 

 of experiments in Alsace, some very encourag- 

 ing figures. An average gain of 7.5 per cent., 

 net, was secured by moderate superheat (44°C.). 

 Messrs. Walther-Meunier, and Ludwig, later, 

 reported again of 13 to 15 per cent, from a super- 

 heat of somewhat greater amount. Schwoerer 

 obtained a gain in efficiency of 15 to 18 per 

 cent, by superheating 68 °C. Hirsch reports 

 similar iigures from an equal amount of gasifica- 

 tion in a marine apparatus. Schroeter obtained 

 gains of 10 per cent, and more in a very elab- 

 orate and detailed investigation, in which the 

 superheat amounted to 60°C. The most re- 

 markable results reported are those of Schmidt, 

 who, by adopting an enormous portion of super- 

 heating to heating surface (six to one), secured a 

 superheat of 190°C., and at another time, with a 



