10 Mr. F. Guthrie on Salt Solutions and Attached Water. 



would tend to make the amount of salt found too small. To 

 this point we shall have to return. 



§ 15. Physical Condition of a Freezing-mixture. — The fact that 

 the rationale of a freezing-mixture is the liquefaction of solids 

 seems to demand at once the conclusion that a freezing-mixture 

 (of say ice and salt) must always be partially liquid. 



Nevertheless, if a mixture be made of about three parts by 

 weight of finely powdered rock-salt and one part of finely crushed 

 ice, the liquefaction which ensues is followed by an apparent 

 regelation so complete that the whole can be handled as a solid 

 mass, and becomes indeed perfectly dry. The cause of this is, 

 I have no doubt, due to the temporary existence of a supersa- 

 turated solution of NaCl + 2H 2 0, a body which is formed at 

 about -10°, Lowitz (-5°, Nolle) (from -3° to -20° continu- 

 ously, F. G.), when saturated brine is artificially cooled. It is, 

 of course, impracticable to separate this substance from the 

 general mass of the freezing-mixture with sufficient precision 

 to allow of its analysis. The phenomenon of solidification 7 

 moreover, only lasts a few minutes. Liquefaction ensues, and 

 the temperature, which had made a pause, again sinks rapidly. 



§ 16. The minimum temperature of a salt-ice freezing-mix- 

 ture seems to be attained between the somewhat wide margins 

 of 3 of salt to 1 of ice, and 1 of salt to 2 of ice. The lowest 

 temperature appears to be —21° to —22° C. 



§ 17. Liquid portion of Freezing -mixture. — It is clear that 

 the liquid portion of a freezing-mixture is a brine of such a com- 

 position as to resist solidification at the temperature of the free- 

 zing-mixture. Accordingly we ought to find that the liquid 

 portion of a freezing-mixture has the same percentage compo- 

 sition as the mother-liquor of a saturated brine from which the 

 bihydrate has been separated out by the external application of 

 an ice- salt freezing-mixture. To test how far this is verified 

 by experience, dry ice and salt were mingled in three pro- 

 portions, namely 3 of ice to 1 of salt, 1 of ice to 1 of salt, and 1 

 of ice to 3 of salt by weight. The salt and ice were in the 

 finest state of division, and the ice was uniformly and as tho- 

 roughly dry as possible. The mixtures were constantly stirred 

 in a wooden bowl for ten minutes, and then thrown upon flannel 

 and pressed through. 



Ice. Salt. NaCl. 



3 1 gave a liquid containing 22*508 



11 „ „ 24-343 



13 „ „ 24-711 



The amount of salt found is therefore not far off that con- 

 tained in the 10 hydrate, namely 24'5. 



