400 MR. J. H. BRINKWORTH ON THE SPECIFIC HEAT OF STEAM AT 



On the Specific Heat of Steam at Atmospheric Pressure between 



104 C. and 115 C. 



By J. H. BRINKWORTH, A.R.C.S., J3.Sc., Lecturer in Physics at St. Thomas's Hospital 



Medical School. 



. 



Introduction. 



With one exception, all the experimental determinations of the specific heat of 

 steam at atmospheric pressure have been made with steam considerably superheated. 

 The first reliable investigations were made by HEGNAULT, and the value he obtained, 

 when corrected for various errors, reduces to 0'475 ; this being the mean specific heat 

 over the range 125 C. to 225 C. Prof. CALLENDAR, using the continuous flow method 

 of calorimetry, has made the one determination previously quoted, in which the 

 specific heat at atmospheric pressure was measured at a temperature not far removed 

 from that of saturation. The value experimentally obtained, 0'493 over the range 

 103 C. to 113 C., is somewhat higher than that deduced by extrapolation from the 

 results of other observers, and requires reduction (as above explained, p. 396) in order 

 to allow for a minute fraction (about 1 in 10,000) of water present in the steam. In 

 consequence, Prof. CALLENDAR suggested to me that a redetermination of the specific 

 heat of steam near 100 C. was desirable. My other duties are such as to allow only 

 a certain amount of time for research, hence this investigation has been rather 

 protracted ; but through the whole course of the work I have been encouraged by 

 Prof. CALLENDAR, and here I wish to record my great indebtedness for the advice he 

 has always given so readily. This investigation has been carried out in the Physical 

 Laboratories of the Imperial College of Science, and I desire to acknowledge the 

 kindness of the Board of Governors in furnishing me with the necessary equipment 

 and with laboratory accommodation for so long a period. 



Outline of the Method. 



Steam is generated in a boiler of about 15 litres capacity and thence led to one 

 limb of a U-tube pressure regulator, to be described in detail later. The pressure of 

 the steam forces the mercury down in this limb of the U-tube and up in the other 

 limb in which the adjustment of the supply of gas to the large ring burner, used for 

 heating the water in the boiler, is made. After passing the regulator, the steam, now 

 maintained at a constant pressure, is led between the walls of a jacket surrounding 

 the calorimeter proper, thence through a separator and a throttle into the space 

 enclosed by the double-walled jacket, whence it passes down the calorimeter flow-tube 

 to a condenser. During the passage of the steam through the flow-tube it is heated 

 by means of an electric current passing through a platinum heating coil, and its 

 temperature is measured on a platinum resistance thermometer. Another temperature 



