132 On Ice and Brines 



This argument appears conclusive. In order to explain 

 all the phenomena observed in connection with sea-water ice 

 he cites Guthrie's investigations, which went to show that, in 

 freezing saline solutions, under a certain concentration, pure 

 ice is formed at a temperature which falls from o C., when 

 the amount of salt dissolved is infinitely small, to a certain 

 definite temperature when the solution contains a certain 

 definite percentage of salt. Further abstraction of heat then 

 produces solidification of the solution as a whole, in the form 

 of a crystalline hydrate, of constant freezing- and melting-point. 

 To such hydrates, Guthrie gave the name of cryohydrates. 

 Petterssori quotes the following as being particularly applic- 

 able to the case of sea-water : 



Solidifies at 

 o r* 



-22 



- 1 1-4 

 -37-0 



- 5-0 



Na 2 SO 4 95-45 - 0-7 



And he refers more particularly to the cryohydrate of Na 2 SO 4 

 forming and melting at o7. 



Now the bearing of Guthrie's experiments is to show 

 that, while at sufficiently low temperatures, and with suitable 

 concentration, the water will solidify along with one or other 

 of the salts in solution, until this low temperature and high 

 concentration are attained, pure ice must be the result of 

 freezing. 



The abnormal phenomena attending the formation and 

 the melting of ice in saline solutions and sea-water find a 

 natural explanation in an observation which I have frequently 

 quoted, and which Dr Pettersson mentions in a footnote at 

 p. 318, namely, that "a thermometer immersed in a mixture 

 of snow and sea-water which is constantly stirred indicates 

 - i'8 C." If this is true, it is clear that my melting-point 

 observations proved nothing. On repeating the experiment 

 I found it confirmed, and took the opportunity this winter 

 of investigating the matter more closely. The paper now 



