422 Prof. Curtis on the Freezing of Water 



compared with each individual steam-particle which enters into 

 its composition, and that the sphere of chemical attraction of the 

 salt cannot penetrate far into the interior of the spherical mass 

 of steam forming a visible bubble. Consequently it may be sup- 

 posed that a steam-bubble of a given weight formed at the bot- 

 tom of the solution should assume a size very nearly equal to 

 that of a steam-bubble of equal weight formed in pure water 

 boiling under the same pressure; and, unless there be some 

 special reason why steam should not be superheated by passing 

 through an aqueous solution considerably hotter than itself, it 

 might be expected that the steam-bubbles formed at the bottom 

 of a mass of a solution of potash or muriate of lime at a tempe- 

 rature of upwards of 270° under atmospheric pressure would 

 show some sign of having acquired a temperature somewhat 

 above 212° in their passage from the bottom to the surface of 

 the liquid. The general accuracy of Regnault's experimental 

 researches is universally admitted ; and his experiments have fully 

 proved the fact enounced by Hudberg long ago, that the steam 

 from aqueous solutions boiling at temperatures above 212° is 

 still only 212°. At the same time I think it will be admitted 

 that Regnault's explanation of the phenomena, though applicable 

 molecularty, does not satisfactorily apply to the passage of visible 

 steam-bubbles through an aqueous solution much hotter than 

 the normal boiling-point of pure water under a given pressure. 

 The subject seems to be still enveloped in obscurity, and requires 

 further investigation. 



Palermo, October 13, 1866. 



LVII. On the Freezing of Water at Temperatures lower than 32°F. 

 By Arthur Hill Curtis, LL. D., Professor of Natural Phi- 

 losophy in the Queen's University*. 



HEN water which has been reduced in temperature 

 below the ordinary freezing-point without becoming 

 solidified is agitated, it is well known that a portion of it be- 

 comes frozen ; and the question immediately arises, how much ? 

 This question has been already answered, and the result arrived 

 at tested by experiment. In obtaining the result, however, it 

 has been assumed that all the ice is formed either at the tempe- 

 rature of 32° F., or at the initial temperature of the water. 

 Now a little consideration will show that neither of these as- 

 sumptions is true. The congelation commences at some one 

 point, or at a certain finite number of points ; certain small par- 



* Communicated by the Author. 



