MR. J. H. BRINKVVORTH ON SPECIFIC HEAT OF STEAM. 399 



with temperature, it appears likely that a constant mean value, such as 0'477, over 

 the range 100 C. to 300 C., will agree better than a variable value with actua 

 practice, in addition to simplifying the theory. 



Later Experiments. 



The differential throttling calorimeter was redesigned for higher pressures and 

 temperatures in conjunction with Prof. DALBY in 1906, and was set up in the 

 laboratory of the City and Guilds Institution (now part of the Imperial College of 

 Science), at South Kensington. The late Prof. ASHCROFT assisted the writer in taking 

 a series of observations on superheated steam. A differential platinum thermometer 

 was employed for reading the temperature difference, and a mercury gauge for the 

 pressure difference. The observations extended to an upper limit of 376 C. and 

 agreed so closely with the variation of the cooling effect predicted by equations (6) 

 and (7), that it was not considered worth while to publish them in detail, as it was 

 hoped to obtain a more complete series at much higher pressures as soon as a suitable 

 boiler and regulator could be installed. Owing to the great increase in the number 

 of students in the engineering department, which necessitated a continual rearrange- 

 ment of laboratories and equipment, it was found to be impossible to proceed with 

 this work at the time. But the opening of the new engineering building is expected 

 to relieve the pressure, and permit the work to be resumed at an early date. The 

 apparatus is designed for simultaneous measurements of S and C under the same 

 conditions, which is particularly advantageous, since both are required in the 

 equations. 



About the same time, preparations were made for attacking the problem of the 

 variation of specific heat with temperature from the theoretical side, by a quantitative 

 investigation of the absorption and emission spectra of gases in the infra red, which 

 must, according to the theory of radiation, be intimately related to the variation of - 

 the specific heat. The elaborate apparatus required for this purpose was made in the 

 physics workshop of the Imperial College, and took some years to construct, in 

 consequence of the great pressure of other work. It was practically completed two 

 years ago, and gave promise of supplying very useful information, but the work has 

 now been brought to a standstill for want of funds to supply the necessary assistance 

 and materials for carrying it on. It is hoped that something may be done towards 

 the solution of this important problem when the assistants now serving at the front 

 are set free at the conclusion of the war, but the work requires two or more observers, 

 and nothing can be done without highly trained assistants, owing to the great 

 difficulty and delicacy of the observations. 



H. L. C. 



VOL. CCXV. A. 3 H 



