THE 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. XXXII. FOURTH SERIES. 



LXVI. On the Temperature of the Vapours of Boiling Saline 

 Solutions. By J. Gill, Esq.* 



IN treating of the temperature of the steam evolved from 

 boiling solutions, it should of course be assumed that the 

 steam consists of pure water free from any vestige of the dissolved 

 substance. With this condition, if the steam at atmospheric 

 pressure is observed to be hotter than the boiling-point of pure 

 water under atmospheric pressure, it must evidently be super- 

 heated; and in investigating this subject experimentally it is 

 essential to ascertain whether this superheat, if it exist, is im- 

 parted to the steam by the hotter boiling liquid itself, and not by 

 conduction or radiation of the walls of the containing vessels. 

 At first sight this condition appears difficult ; even in Regnault's 

 apparatus for graduating thermometers, if the boiling liquid were 

 sensibly hotter than pure water boiling under the same pres- 

 sure, the conduction of heat upwards through the walls of the 

 vessel would communicate some heat to the steam, though pro- 

 bably not of appreciable amount if the formation of steam were 

 comparatively rapid. In the experiments of Professor Magnus f 

 with solutions whose boiling-point was in some cases as high as 

 118°, the conduction of heat upwards through the metal of the 

 apparatus must have been considerable, and could not fail to 

 produce marked effects on the thermometer, both by superheating 

 the steam by contact and radiation, and by radiation on the ther- 

 mometer itself, if the current of steam were slow. 



Gay-Lussac enounced long ago that the temperature of the 

 vapour of any boiling liquid is the same as the temperature of the 

 liquid itself at the spot where the vapour is formed ; and Faraday J 



* Communicated by the Author. 



t Poggeudorff's Annalen, vol. cxii. p. 408. 



X Quarterly Journal of Science, 1823. 



Phil. Mag. S. 4. No. 219. Suppl. Vol. 32. 2 I 



