136 ROYAL SOCIETY OF CANADA 



was placed in the steam pipe a little in front of the steam chest of No. 1 

 cylinder, and during the trials only a few ounces of water were ever 

 obtained from the drain pii)e leading from the separator. Two calori- 

 meters of the separating and throttling kind, ])laced after the separator, 

 showed to within the I'ange of the instrument the steam to be practically 

 dry. in line 46 of the tables is given the amount of steam used per I.H. 

 P. ])cr hour. A comparison made by this between tlie jacketed and 

 unjacketed trials is scarcely fair to the former, as the jacket steam gives 

 up to the cylinder only its latent heat, whilst the remaining heat in it is 

 available to raise the tem]ierature of the feed water. Line 60 which 

 gives the thermal units used per I. H. P. per minute reckoned from 1 10° 

 F. for the cylinder feed, and including only the latent heat of the jacket 

 steam, will afford, it is thought, a better means to compare all the trials. 

 According to Elliott and Willans, it is useless, in a condensing engine, to 

 allow the steam to expand after the temperature has reached about 110° 

 F. This then fixed a lower limit of temperature for the perfect engine. 

 For a perfect unjacketed engine, where no heat is allowed to pass either 

 from or into the working cylinder, the expansion will be adiahatic. A 

 pound of steam expanding adiabatically from a temperature T^ to a 

 temperature T„ ought to be capable of doing an amount of work express- 

 ed in thermal units l)y the following formula : 



jT, to T„ being absolute temperatures measured in degrees Fahrenheit, 

 and Xj the latent heat of the steam at temperature T^ . The ratio of the 

 work actually obtained to this ideal amount gives what is here called the 

 Willans efficiency. "With the jacketed trials, the amount of ivork due 

 per lb. of steam used, is less than in the unjacketed trials, seeing that, as 

 above stated, only the latent heat of the jacket steam is used. To 

 calculate the amount of work due per lb. of steam in this case, the ratio 

 of the cylinder feed and of the jacket feed to the total steam used has 

 been found. The jacket feed fraction has then been midtiplied by the 

 ratio of the latent heat to the total heat in the steam at its temperature. 

 This newly found fraction is then added to the cylinder feed fraction 

 found before. This gives a multiplier, less than one, the product of 

 which and the thei-mal units due from one pound of steam, calculated on 

 the assumption just before mentioned, gives a new quantity representing 

 the work due from a lb. of steam as supplied to the jacketed trials. 

 Owing to the thermodynamic inefficiency of jacketed engines, due to the 

 fact that all the heat supplied to the working substance is not supj)lied at 

 the highest temperature, the result thus obtained will give a higher 

 number of thermal units than could be obtained from that type of engine. 

 It is however possible to imagine a motor, which could use steam contain- 

 ing the same quantity of heat units, in the most advantageous way, that 



