May 5, 1887] 



NATURE 



II 



Table VIII. 



Acid dissolved. 



Temperature of 

 melting ice. 



HCl. 



H2SD4. 



Per cent. H in solution. 



The temperatures given in these tables are all in terms 

 of the same thermometer, which has not been verified for 

 this part of its scale by comparison with a standard or 

 with the air thermometer. 



It is exceedingly difficult, as a rule, to ascertain the 

 trustworthiness of a thermometer at low temperatures. 

 This difficulty would be removed if the temperature at 

 which ice melts in solutions of some very soluble salts of 

 different concentrations were carefully and accurately 

 determined with a good air thermometer. If, for instance, 

 this were done for chloride of calcium solution, which in 

 many ways would be a particularly convenient one, there 

 would be no difficulty in verifying a thermometer at any 

 moment at temperatures as low as - 30'' C. by mixing 

 pounded ice with the strong solution, immersing the 

 thermometer in it, taking a series of readings of the in- 

 strument, while a series of samples of the liquid is taken 

 and in them the chlorine determined. There are consider- 

 able advantages in this method of verification of ther- 

 mometers by chemical means, especially as it obviates the 

 use of the air thermometer, which is always inconvenient. 

 The experiments of Pfaundler and Schnegg on the 

 freezing of aqueous solutions of sulphuric acid can be used 

 for this purpoie. But it would be better to have a series 

 of observations made for the purpose with the more con- 

 venient chloride of calcium solution. 



Freezing Mixtures. — The results obtained in examin- 

 ing the melting-point of ice in saline solutions affords 

 data for mixing freezing baths of any degree of cooling 

 power. With chloride of sodium, for instance, a rough 

 rule is to have such an amount of salt dissolved in the 

 brine that the percentage of chlorine shall give the de- 

 sired temperature in Centigrade degrees below the freezing- 

 point. In my experiments in freezing sea-water in 

 quantities of 300 grammes, I usually made up the bath 

 of 500 grammes pounded ice, 400 grammes water, and 

 45 grammes common salt. . When mixed, the liquid con- 

 tained about 4 per cent. CI, and gave a temperature a 

 little below -4° C. In the course of an hour the liquid 

 would contain 3 per cent, to 3-25 per cent. CI, and the 

 temperature have risen to -3° C. By using such baths 

 freezing operations can always be kept completely in 

 hand. 



Summary. — Owing to its peculiar physical properties it 

 is impossible to prepare the crystalline solid which separ- 

 ates from sea-water and analogous saline solutions in a 

 condition to enable the question, whether the salt does or 

 does not form part of the solid matter of the crystals, to 

 be solved directly by chemical analysis. 



So far as chemical analysis is applicable, it is in favour 

 of the salt belonging exclusively to the adhering brine. 

 When sea-water is carefully frozen' artificially, the ratio 

 between the chlorine and the sulphuric acid is the same 

 for the solid contents of the original water, the crystals, and 

 the mother-liquor. It is exceedingly unlikely if part of the 

 salt went into the crystals, leaving the remainder in the 



brine, that there would be no selective separation of its 

 constituents. 



It has been shown (and the whole of the second part 

 of the paper is taken up with this subject) that snow or 

 pure lake ice, which, when melting by itself or immersed 

 in pure water at atmospheric pressure, melts at the constant 

 temperature called 0"" C. or 32° Fahr., changes its melting 

 temperature when immersed in a saline solution. The 

 altered melting temperature, however, is the same for 

 solutions of the same composition (no doubt with some 

 allowance for pressure) and different for solutions of 

 different composition. 



The temperature at which pure ice melts in a solution 

 is identical with that at which ice separates from the same 

 solution on being sufficiently cooled. 



When sea-water is frozen to the extent of 15 per cent, 

 of its mass, and the crystals so formed are allowed to melt 

 in the liquid in which they have been produced, they melt 

 exactly as they have been formed. If snow or pure ice 

 be immersed in the brine formed by partially freezing sea- 

 water, it melts at the same temperature as the ice which 

 had been formed by freezing the sea- water, so long as the 

 chemical composition is the same in each case. 



When saline solutions are cooled for a sufficient length 

 of time at a sufficiently low temperature, there arrives a 

 certain concentration at a certain temperature, when further 

 removal of heat causes solidification of the brine as a 

 whole (cryohydrate). 



The concentration necessary for the solidification of even 

 the cryohydrate of highest melting temperature is such 

 that in \h.Q. primary freezing of sea-water in nature no such 

 body can be formed. It would follow from this consideration 

 alone that the first ice formed on the sea in Arctic regions 

 consists of pure ice, and it is also certain that it would 

 retain a large quantity of the residual sea-water in its 

 interstices. During the winter this inclosed liquor would 

 solidify in the interstices of the crystals to ice and cryo- 

 hydrates, in so far as the temperature and the nature of the 

 salts in solution would permit. From my experiments 

 with chloride of calcium, and the existance of brines 

 observed to remain liquid at - 30^ C. at the winter-quarters 

 of the Vega, it is unlikely that sea-water, as a whole, can 

 ever be completely solidified in nature. The presence of 

 unfreezable or difficultly freezable brine in freshly-formed 

 sea-water ice explains its eminently plastic character even 

 at very low temperatures. The presence of similar 

 unfrozen brine in natural land ice at temperatures neigh- 

 bouring to o^ C. explains its slightly plastic character, 

 which is sufficient to account for the slow fluid motion of 

 glaciers under the long-continued pressure of their own 

 weight. 



The fact that cryohydrates of different salts solidify 

 and melt at different temperatures, sufficiently explains 

 the various composition of different specimens of old sea 

 ice. 



The physical phenomena observed in freezing sea-water 

 and saline solutions of moderate concentration, are all 

 easily and simply explained on the hypothesis that the 

 crystalline body formed is pure ice. Thus, the heat 

 removed in freezing sea-water to the extent of 1 5 per cent, 

 of its mass accounted for the production of the same 

 amount of ice as was given by calculation on the basis of 

 the chlorine found in the mother-liquor. 



The apparent expansion, near the melting-point, of ice 

 formed by the freezing water which contains any salt at 

 all is perfectly explained on the hypothesis that in the act 

 of freezing the water rigidly excludes all saline matter from 

 participation in its soHdification. 



The same applies to the latent heat of water containing 

 salt in matter. Pettersson made two determinations of 

 the latent heat of sea-water containing 1-927 per cent. CI 

 and 3-53 per cent. salt. The freezing took place in the 

 one case batween the temperatures -g'-oand -7^-47 C., 

 and in the other between -8^-35 and -6°-94 C, and the 



