804 TRUEBLOOD. 



obtained without a great outlay of time in experimental work. While 

 the radial flow plug thus appears to be much superior to the axial flow 

 plug, it is pointed out that the axial flow plugs used in this research 

 have a serious structural defect which a better design would avoid; 

 hence the superiority of the radial flow plug, though doubtless actual, 

 is not so great as a cursory inspection of the results exhibited graphi- 

 cally would indicate. The final apparatus is designed to permit more 

 exact tests of the relative merits of the two types of plug: these have 

 not as yet been made. 



5. The value 3.182 degrees Centigrade per kilogram per square 

 centimeter is given for the Joule-Thomson coefficient in steam at 

 165° C. and 3.86 kgm./cm.^ This is believed to be reliable to within 

 0.5 per cent. 



6. The results of some early isothermal experiments giving directly 

 the product jj-Cp are briefly summarized. An agreement wathin about 

 2.5 per cent, with the above value of /x is obtained by dividing 

 the mean fxCp as derived from these experiments by Knoblauch and 

 Mollier's value of Cp. 



7. The question of the existence of a pressure coefficient of /x is 

 discussed. This is of interest because the experiments from which 

 the above value of fx is derived were not conducted at exactly the same 

 mean pressure and were not corrected for the existing small differences 

 in their mean pressures. A few experiments made by the writer 

 indicate the existence of a small positive pressure coefficient. This 

 is in verification of the recent steam equation of Goodenough. It is 

 believed that the resulting correction in the above value of /x, which 

 can not yet be made accurately', is less than 0.3 per cent. 



8. It is shown that the above value of n is in good agreement 

 (within less than 1 per cent.) with the mean of the results of Grindley, 

 Peake and Griessmann at the same temperature. 



The work which has been described in the foregoing paper was 

 undertaken at the suggestion and under the direction of Professor 

 H. N. Davis, to whom the writer has been indebted for constant advice 

 and for much assistance of a practical and positive sort, only part of 

 which has been explicitly mentioned in the body of the paper. 

 Acknowledgment should also be made to the Rumford Committee 

 of the American Academy of Arts and Sciences for a grant to Prof. 

 Davis, a considerable part of which was used to further this work. 



