Decembee 2, 1898.] 



SCIENCE. 



765 



phenomena in the engine as well as at the 

 boiler, and exemplifies the case by making 

 "the diagram a correct measure, drawn to 

 scale, of the performance of a famous steam 

 pumping engine. 



All the required data for exhibition of 

 this flow of the energies through a heat- 

 engine are secured and recorded in every 

 well conducted and complete engine-trial, 

 and ample data are now available for its 

 illustration. One of the best of recent re- 

 ports upon the performance of the excep- 

 tionally economical Leavitt engine at the 

 Louisville, Ky., water works has been dia- 

 grammed in this manner by Captain Sankey, 

 to make clearly understood the principles 

 and the facts involved in the discussion of 

 the 'thermal efiSciency of steam-engines,' 

 by this committee of the British Institution 

 of Civil Engineers. This diagram is here 

 reproduced, from that report, published 

 as above. In this instance, every known 

 precaution against waste of heat has been 

 taken, and all the conditions, thermal, 

 thermodynamic and dynamic, are in un- 

 usual degree favorable to a high resultant 

 efficiency. The case is, therefore, a very ex- 

 ceptionally good illustration of thermody- 

 namic action, and the wastes are much 

 smaller than are commonly observed in the 

 operation of even good classes of steam- 

 engine. 



" The broad river of heat, generated by 

 the burning coal on the grate, is shown 

 flowing to and through every part of the 

 apparatus, losing by radiation at every step, 

 and finally emerging at the chimney, in a 

 flow of heated air and gases, and at the 

 condenser, in the circulating water dis- 

 charged, and at the engine-shaft as useful 

 work." All of this broad river of heat 

 arises from a source within the fuel bed, 

 flows through its delta of narrower chan- 

 nels, mainly to waste, and it all finally 

 emerges into the great sea of heat, the ex- 

 ternal atmosphere, as thermal energy ; even 



the useful work being sooner or later re- 

 transformed into heat by friction, whether 

 of engine or of work performed by the 

 machine. Were our diagram to give the 

 further history of these flows of energy it 

 would show a cycle in which the external 

 currents circulate from the engine into the 

 atmosphere, into potential forms, once more, 

 by retransformation into the stored energy 

 of chemical affinities, through the ever-ac- 

 tive influence of vegetation, later to be pos- 

 sibly again employed in other heat-engine 

 cycles, when once more resurrected as po- 

 tential energy of fuel.* 



The diagram here reproduced is drawn to 

 a scale, and quantities of heat, and tempera- 

 tures as well, are shown at each step in the 

 progress of the heat flow, from fuel to outer 

 atmosphere and to the drainage channels 

 of the country. The following verbal 

 description may properly accompany the 

 graphic story : 



At the start, 183,600 B. T. U. per min- 

 ute is the measure of the energy liberated 

 in active form from its original, potential, 

 condition in the fuel. Of this energy, 131,- 

 700 B. T. U. pass into the water and steam 

 and are there stored as thermal energy, 

 available for thermodynamic operations; 

 41,900 go toward chimney and economizer; 

 10,000 flow out of the system, as waste, 

 through condition and radiation in the flow 

 between boiler and economizer, 5,000 more 

 at the economizer, and 15,750 are taken 

 into the feed-water within the economizer 

 and thus utilized. The balance, 20,150, 

 get through the economizer and flow up 

 chimney and thus into the outer air and 

 are lost to the thermodamic system. 



The economizer receives 5,450 B. T. TJ. 

 from the feed-water coming from the en- 

 gine and 15,750 from the furnace-gases ; 



''' For original data of the case here taken, see 

 Trans. Am. Society Mechanical Engineers, Vol. XVI., 

 Engineering News, December 13, 1894. Proc. Brit. 

 Inst. C. E., 1898. 



