November 27, 1896.] 



SCIENCE. 



781 



from danger of burning out at light loads, 

 while giving suitable action at heavy loads. 

 In the one case it must supply a small 

 amount of highly superheated steam to the 

 engine, in the other a larger quantity with 

 less superheat. 



This presents the engineer with a prob- 

 lem not yet really attacked. 



(9) The average simple engine may be 

 said, under such conditions as we are most 

 familiar with, to demand a quantity of fuel 

 annually, about equal in value to its own 

 first cost. In such cases it is obvious that 

 under these conditions, and with the above 

 return of five dollars in saving to. each dol- 

 lar paid to thus reduce waste, it will pay to 

 annually expend the full equivalent of the 

 interest on the price of the engine in main- 

 taining a good superheating system. When, 

 however, as has usually hitherto happened, 

 this account includes such large interest 

 and wear-and-tear accounts as cause the 

 total annual expense to exceed this financial 

 limit, the engineer will wisely decline to 

 thus invest capital. 



Studying the results of experiments to 

 date determining the magnitude of the in- 

 ternal wastes which superheating is ex- 

 pected to reduce, we shall find that the fol- 

 lowing may be taken as, roughly, the meas- 

 ure of those wastes, the relative quantities 

 of heat gained by their complete extinction 

 and the extent of the necessary superheat : 



GAIN BY SUPERHEATING. 



(10) Given a safe and durable and effi- 

 cient superheater, and the engineer will 

 have the power to adjust his temperatures 



and pressures of working fluid to any limit 

 that may be sent by the character of his 

 materials in boiler and engine, and to se- 

 cure the best adjustment of the thermal to 

 the dynamic limit. 



In other words, he may produce a work- 

 ing fluid having at once the high tempera- 

 ture and wide range of adiabatic expansion 

 requisite for maximum thermodynamic effi- 

 ciency, and the high initial and mean effec- 

 tive pressures needed to insure maximum 

 dynamic efficiency or efficiency of the 

 mechanism of the engine ; the two combined 

 thus giving the maximum total efficiency 

 obtainable by any means whatever. The 

 high thermodynamic efficiency of the gas 

 engine and the peculiarly high ' efficiency 

 of machine ' characteristic of the steam-en- 

 gine would be both secured, and the steam- 

 engine once more placed beyond rivalry 

 among all the heat-engines. 



(11) This is, to-day, the greatest of all the 

 problems presented the designing and con- 

 structing engineer, with the possible excep- 

 tion of that of finding a system of effectually 

 rendering the interior of the working cylin- 

 der non-conducting, in such manner as to 

 prevent entirely the occurrence of initial 

 condensation, thus conforming the ' ideal 

 case ' to the real, and making the steam 

 engine a purely thermodynamic machine.^ 



The above are the main points of the 

 paper, so far as especially interesting from 

 a scientific point of view. It includes, in 

 a monograph of some seventy pages, a col- 

 lection of facts, data, and results of experi- 

 ence and of direct experimental tests of 

 engines and boilers, as well as opinions of 

 distinguished authorities and practitioners, 

 which, while valuable as a basis for its de- 

 ductions and final conclusions, would be out 

 of place here. But even these omitted 

 sixty pages constitute but a fraction of all 



* ' The Final Improvement of the Steam Engine, ' 

 E. H. Thurston. Transactions United States Naval In- 

 stitute, 1891 ; Sibley Journal of Engineering, 1892. 



