EXPERIMENTAL STUDY OF HEAT LEAKAGE. 735 



^\^lile the results obtained wath the latest type of radial flow appara- 

 tus used justify the conclusion that the heat leak problem has been 

 satisfactorily solved, there is little of value, in the results here pre- 

 sented, to those who are primarily interested in the thermodynamics 

 of superheated steam, since the work covers the determination of n 

 at only one point. The experimental work at other points is now in 

 progress, and it is expected that its results will be set forth in a future 

 paper. This further prosecution of the work has been made possible 

 by the generous loan of most of the necessary apparatus to the writer 

 by the Director of the Jefferson Physical Laboratory of Harvard 

 University. All of the results presented and discussed in this paper 

 were obtained in the Jefferson Laboratory. 



IL THE THROTTLING APPARATUS. 



In all the work described and discussed in this paper, the throttling 

 apparatus, whether of the radial or axial flow type, was immersed in 

 an oil bath, the temperature of which was automatically maintained 

 constant. This oil bath also contained a device, hereafter called the 

 secondary superheater, consisting of a coil of pipe or of pipes, through 

 which the steam was passed before reaching the high side of the plug. 

 With this arrangement, very common in throttling calorimetry, the 

 temperature of the fluid on the high side of the plug is presumably 

 that of the bath, at least if the velocity of flow of the fluid when in the 

 secondary superheater is the same as it is at the high side thermometer 

 bulb. For fluids with positive Joule-Thomson effects, the heat leak- 

 age is therefore from the bath inward to the fluid, if the fluid is merely 

 throttled without other addition of heat. 



1. Axial Flow Apparatus. 



The general type of axial flow porous plug (a term here used in 

 contradistinction to the term 'radial flow plug,' which is the other 

 fundamental type involved in these experiments) is illustrated in 

 Fig. L The steam enters at one of the orifices near the top of the 

 cap C, passes the high side thermometer (not shown, but screwing 

 into the bushing M), thence through the numerous fine holes shown 

 in section in the soapstone block S, through the cross channel in the 



