484 Mr. J. Gill on the Temperature of the 



steam supposed to be at 100°, according to Rudberg's deductions 

 confirmed by Regnault. According to the experiments of Pro- 

 fessor Magnus*, the temperature of the steam should be about 

 ] 06°. . The fact shown by the experiment I am describing is, that 

 the withdrawing of the brine from the thermometer, and the con- 

 sequent circumstance of its being left in an atmosphere of steam 

 formed and forming from this brine under atmospheric pressure, 

 did not cause any marked effect on its indication of temperature, 

 which remained during some minutes nearly steady at 109°. 

 The time could not be greatly prolonged, as the salt thrown 

 down from the evaporating liquid might cause the bottom of the 

 vessel a to get injured by the flame ; however, the interval was 

 long enough to show that the thermometer indicated very little 

 tendency to lower its temperature ; and if the initial circum- 

 stances of the experiment could be kept constant, there is every 

 probability that the thermometer would remain steady at the 

 initial temperature of 109°, although surrounded by steam at 

 100°. It may also be assumed that the temperature of the shell 

 b is the same as that of the thermometer, at the moment when 

 the boiling brine is run off. The sustained temperature of the 

 thermometer must be attributed to the direct thermic action of 

 the steam by contact, or to radiation, or to both these causes 

 together ; it is probable, however, that the direct action of the 

 current of steam, even with slow boiling, would greatly exceed 

 that of radiation ; and allowing that the steam might, on leaving 

 the liquid, have a temperature of about 106° (as found by Mag- 

 nus) with solutions boiling at 109°, the combined effect of this 

 temperature and of radiation from the interior surfaces of the 

 apparatus at 109° is still not sufficient to account for the nearly 

 steady temperature of 109° shown by the thermometer. The 

 only obvious explanation would be to suppose the steam to be 

 actually superheated to 109°. This point was decided as fol- 

 lows : — 



As the previous experiment had lasted some minutes, and there 

 was some risk of the bottom of the vessel a -getting injured from 

 a deposit of salt, the contents were emptied out and the vessel 

 was filled with a fresh portion of the original saturated brine to 

 the upper level g as before. After it had been boiling a short 

 time, the thermometer No. 1 indicating 109°, the brine was 

 slowly drawn off to the level h as before, and during one minute 

 the thermometer was observed to remain steady at 109°. The 

 flame of the lamp was kept as nearly as possible steady. It was 

 supposed that thus things were in the same condition as in the 

 previous experiment ; and it remained to ascertain (if possible) 

 the real temperature of the mass of steam. A second thermo- 



* Annates de Chimie, 3 ser. vol. xii. p. 376, from Poggendorff's Annalen. 



