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PROCEEDINGS OF THE AMERICAN ACADEMY. 



mist into a homogeneous state. Knoblauch and Jakob say that traces 

 of moisture were observable through several of the mixing sections, 

 and it is easy to show that even if" several " means as few as two, and 

 even if the steam in these sections had always had the greatest specific 

 volume which it ever had, the floating mist must have persisted for a 

 time which was never less than a second and averaged more than two 

 seconds, and this after all of the heat necessary for the high superheat 

 had been put in. In Thomas' apparatus, on the other hand, the evapora- 

 tion and superheating had to take place in 2-4 quarter-inch holes in a 

 soapstone block something like 5 inches long, and in a small chamber 

 joist above it, and a similar computation shows that even if the specific 

 volume of the steam had never been greater than that of the original 

 saturated steam, it must have passed the thermocouple, always within 

 nine tenths of a second, sometimes within a thirtieth of a second, and 

 on the average within less than half a second of the time when the 

 first of the superheating heat was put in. It is, therefore, very proba- 

 ble that Thomas' "saturated steam" was slightly wet, and that the 

 percentage of moisture passing the thermocouple decreased from ex- 

 periment to experiment as the final superheat was increased, giving 

 too high values of C p near saturation. Knoblauch's values have there- 

 fore been used in preference to Thomas' in this work. Confirmations 

 of this decision will be found on pages 287, 298 and 302. 



3. The Total Heat of Saturated Steam. 



i A. The determination of 



H — //ioo- — A part of the fol- 

 lowing account of the method 

 by which the total heat of satu- 

 rated steam has been computed 

 is reprinted with minor changes 

 from the Proceedings of the 

 American Society of Mechan- 

 ical Engineers. 



Let Figure 3 represent a 

 throttling curve of the sort 

 published by Grindley, Griess- 

 man or Peake. Supposedly 

 dry and saturated steam at 

 the pressure and temperature 

 corresponding to the point A is first throttled to lower pressure and 

 temperature corresponding to the point B j then in a later experiment 



Fig. 3. 



Fig. 4. 



Showing how the Total Heat Curve 

 ab'c'd' is obtained from a Throttling 

 Curve ABCD. 



