the Therin,o-dynamiccd Properties of Superluated Stetmi.. 83 



eiice could not be distinguished, it being remarked that if the dryness of 

 the steam before passing the orifice had been altered by so little as 

 0'06 per cent., a difference of 1°F. should have been observed in the 

 temperature of the wiredrawn steam. 



It would, therefore, appear that saturated steam at any particular 

 pressure obtained by relieving it of suspended moisture by gravitation 

 has only one condition as to its dryness, and also that steam in this 

 particular condition was obtained both in these experiments and in 

 those of Regnault, and it is therefore taken that the steam before wire- 

 drawing has a total heat given by Eegnault's tables of the total heats of 

 saturated steam. 



Fiu'ther experiments were also made to observe the eft'ect of altering 

 the position of the thermo-electric junction in the wiredrawn steam, of 

 the effect of the steam jacket on the temperature of the wiredrawn 

 steam, and of the effect of the velocity of the steam through the apparatus 

 on these teniperatm^e readings. The amount of the corrections required 

 for the conduction of heat between various portions of the apparatus 

 and the steam was. also calculated, but on account of the precautions 

 taken these were geneially found to be negligible. The method of fixing 

 the absolute temperature of the wiredrawn steam should be here men- 

 tioned, as it is a point of great importance, on account of the diffi- 

 culties attending the accurate measurement of the temperature. In 

 the experiments the thermometer was used merely as a scale to compare 

 the temperature of the wiredrawn steam with that of saturated steam 

 under a known pressure flowing through the same portions of the appa- 

 ratus with about the same velocity, the fixing of the temperature being 

 again dependent on Eegnault's tables of the pressure-temperature rela- 

 tion of saturated steam. 



The final results obtained show clearly that within the limits of tem- 

 perature obtained by wiredrawing saturated steam at temperatures 

 varying from 240° to 380° F., the condition of the steam known as a 

 perfect gas was not obtained, even when the wiredrawing was con- 

 tinued to 3 lbs. or 4 lbs. per square inch absolute pressure ; and further, 

 that between the same temperatures and between pressures of 2*5 lbs. 

 and 195 lbs. per square inch, there was not found any indication of a 

 constant value of the specific heat at constant pressure in the super- 

 heated steam. The specific heat at constant pressure was found to 

 increase with temperature, the mean specific heat at atmospheric 

 pressure between the temperatures 230'7° and 246*5° being 0*4317, 

 and between temperatures 295° and 311-5° the mean specific heat was 

 0*6482. 



As regards the variation in the value of the specific heat at con- 

 stant pressure of superheated steam with the pressure, it appears 

 from an examination of the results obtained at about the same tem- 

 perature but under different pressures, that if any such variation in the 



