MR. J. H. BRINKWORTH ON SPECIFIC HEAT OF STEAM. 



389 



SEPARATOR 

 LAGGING 



THROTTLE 



to determine the magnitude of the steam current, which could be varied in any 



desired ratio, within certain limits, by fitting throttles of different sizes. Apart from 



barometric variations, which were generally small, any desired current could be 



maintained constant to about 1 in 1000. After passing the throttle, the steam at 



atmospheric pressure, already slightly superheated, was raised very nearly to the 



temperature of the jacket by passing through a 



number of gauze discs. In the earlier experiments, 



the temperature of the steam on entering the vacuum 



jacket was taken by a platinum thermometer before 



reaching the heating coil. In many of the later 



experiments this thermometer was omitted, because 



the measurement was found to be superfluous, owing 



to the extreme steadiness of the regulator. The 



heating coil was of platinum, wound on a mica frame, 



having a resistance of about 5'5 ohms at 110 C. It 



was provided with current and potential leads, and 



connected in series with a 5-ohm manganin standard 



for measuring the current in the usual way. The 



leads to the heating coil were insulated by glass 



tubes (not shown) round which the steam, after 



passing the heating coil, was made to circulate 



spirally by a rubber coil or metal spiral nearly fitting 



the flow tube. The thermometers consisted of coils 



of silk-covered platinum wire, each having a funda- 



mental interval of 1 ohm, and capable of sliding up 



or down in small bore tubes, 3'5 mm. diam., with the 



object of interchanging thermometers, and varying 



the immersion when desired. The bulbs were gener- 



ally fixed at a distance of 10 cm. from the heating 



coil, to allow time for the mixing of the steam to 



a uniform temperature. The coils were wound on 



glass, and the copper leads were insulated by glass 



capillaries. 



It would be tedious and unnecessary to describe 

 in detail all the different arrangements adopted for 

 measuring the specific heat, and the steps by which 



VACUUM 

 JACKET 



INLET 



OUTLET 

 HERMOMETER 

 TUBES - 



Fig. 3. 



improvements were effected, but the following summary of observations taken with the 

 apparatus above described, shortly after the reading of the paper on June 21st, 1900, 

 is instructive as illustrating some of the difficulties of measurement in the immediate 

 neighbourhood of the saturation point. The temperatures tabulated under tf, &' are 

 the initial and final superheats reckoned from 100 C, The rise of temperature 



