DAVIS. 



CERTAIN THERMAL PROPERTIES OF STEAM. 



301 



which can then be reduced to suitable absolutely constant volumes by 

 interpolation. The curves thus obtained are, however, irregular, and 

 furthermore they show unmistakable evidences of a phenomenon ex- 

 actly analogous to the wet steam error into which Thomas is believed 

 to have fallen. The presence of this error, which took the form of 

 surface condensation in the experimental bulb as saturation was 

 approached, is specifically mentioned by the authors, but no attempt 

 was made to eliminate it on the ground that, "however interesting 



Figure 14. Values of Cp computed by Planck's method from the volume 

 measurements of Ramsay and Young (circles) and of Battelli (dots). 



from a theoretical point of view the absolute expansion of water-gas 

 may be, in practise it is always in contact with a surface ; and an 

 indication of the behavior of steam in contact with glass cannot fail to 

 be of use in considering the practical case of steam in contact with 

 iron." It is therefore interesting to find that the values of C p which 

 have been computed from the data of Ramsay and Young and which 

 are plotted as circles in Figure 14, run close to Thomas' saturation 

 curve. This agreement is an indication that both are subject to the 

 same error. 



Battelli was also troubled by surface condensation, but was at great 

 pains, in discussing his results, to eliminate its effects. It has there- 

 fore seemed best to work not from his data, but from a table near the 



