April 28, 1887] 



NA TURE 



611 



duced bv the formation of a crystal of ice being immediatel)' 

 eliminated bv the mass of water below. In the interstices 

 of the crystals there will be retained a weight of slightly 

 concentrated sea-water at least as great as that of the ice 

 crystals. These retain the brine in a meshwork of cells, 

 and, as the thickness of the ice covering increases, and 

 the freezing surface becomes more remote, the ice and the 

 brine become more and more exposed to the atmospheric 

 rigours of the Arctic winter. The brine will continue to 

 deposit ice until its concentration is such that, for ex- 

 ample, the cryohydrate of NaCl is ready to separate out. 

 It probably will separate out until it comes in conflict 

 with, for instance, the chloride of calcium or the chloride 

 of magnesium, which will retain some of the water, with- 

 out solidifying, even at the lowest temperatures. At the 

 winter quarters of the Vega brine was observed oozing 

 out of sea-water ice and liquid at a temperature of - 30' C. 

 It was very rich in calcium and especially magnesium 

 chlorides. In fact, // is probably quite impossible by any 

 cold occurring in nature to solidify sea-water. 



The residual and unfreezable brine w^hich remains in 

 considerable quantity liquid when sea-water is frozen, 

 must also' remain in greater or less quantity when fresh 

 water is frozen. All natural waters, including rain-water, 

 contain some foreign and usually saline ingredients. If 

 we take chloride of sodium as the type of such ingredients, 

 and suppose a water to contain a quantity of this salt 

 equivalent to one part by weight of chlorine in a million 

 parts of water, then we should have a solution containing 

 o'oooi per cent, of chlorine, and it would begin to freeze 

 and to deposit pure ice at a temperature of -o^'oooi C. ; 

 and it would continue to do so until, say, 999,ooo parts of 

 water had been deposited as ice. There would then 

 remain 1000 parts of residual water, which would retain 

 the salt, and would contain, therefore, o'l per cent, of 

 chlorine, and would not freeze until the temperature had 

 fallen to — o'l C. This water would then deposit ice at 

 temperatures becoming progressively lower, until, when 

 900 more parts of ice had been deposited, we should have 

 100 parts residual water, or brine as it might now be called, 

 containing 1 per cent, of chlorine, and remaining liquid at 

 temperatures above - I'o C When 90 more parts of ice 

 had been deposited, we should have 10 parts of concen- 

 trated brine containing 10 per cent, of chlorine and remain- 

 ing liquid at - 10' C. In the case imagined, we assume 

 the saline contents to consist of NaCl only, and with further 

 concentration the cryohydrate would no doubt separate out 

 and the mass become really solid. On reversing the opera- 

 tions, that is, warming the ice just formed, we should, 

 when the temperature had risen to - 10" C, have 999,990 

 parts ice and 10 brine containing 10 per cent, chlorine. 

 Now, owing to the remarkable fact (which is dealt with 

 at length in the second part of the paper) that pure ice, 

 in contact with a saline solution, melts at a temperature 

 which depends on the nature and the amount of the salt 

 in the solution, and is identical with the temperature at 

 which ice separates from a solution of the same composi- 

 tion on cooling, the brine liqueiies more and more ice at 

 progressively rising temperatures, until, as before, when 

 the temperature of the mass has risen to -o'l C, it 

 consists of 999,000 parts of ice and 1000 parts of liquid 

 water, containing I part of chlorine. The remainder of 

 the ice will melt at a temperature gradually rising from 

 -o'l C. to o^ C. 



The consideration of this example furnishes an easy 

 explanation of the anomalous behaviour of ice, formed 

 from anythmg but the very purest distilled water, in the 

 neighbourhood of its melting-point. This subject has been 

 studied with great care and thoroughness by Pettersson. 

 The apparent expansion of all but the very purest ice, when 

 cooled below o' C., is ascribed by him in part to solid 

 saline contents of the ice which exercise a disturbing and 

 unexplained influence on its physical properties. Viewed 

 in the light of the fact that the presence of even the 



smallest quantity of saline matter in solution prevents 

 the formation of ice at 0° C. and promotes its liquefaction 

 at temperatures below o' C, we see that this apparent 

 expansion of the ice on cooling is probably due to the 

 fact that we are dealing not with hoinogeneous solid ice 

 but with a mixture of ice and saline solution. As the 

 temperature falls this solution deposits more and more 

 ice and its volume increases. But the increase of volume 

 is due to the formation of ice out of water and not to the 

 expansion of a crystalline solid already formed. 



In Table III. are given the volumes occupied by the 

 ice (with inclosed brine) formed by freezing 100,000 c.c. 

 (at 0° C.) of a water containing chloride of sodium equi- 

 valent to 7 grammes chlorine in 1,000,000 cubic centi- 

 metres (at o* C). 



Table III. — Water conlainingT pans CI in 1,000,000. 



,,, . J Brine Ice Petterssjn 



Water Ice remain- and III Vol of 



Temp. froze.!. formed. • ^ R.ir,., :,-« ok -r ^\^- 



»C. C.C. c.c. '^"1; "^""f- cc. 



T Vi z'l /'\ I', P P -v^ 



- 007 99000 107979 looo 108979 roSgSo r 



- o-io 99300 108306 700 109006 109007 I 



- 0-15 99S3J 10S561 467 10902S 10903S 10 



- O-20 99550 10S687 350 109037 109048 II 



- 0-40 99825 10S879 175 109054 109057 3 



The volume of the ice formed on freezing this water is 

 compared with that observed by Pettersson in freezing a 

 sample of the distilled water in ordinary use in the 

 laboratory. 



It will be seen that the volumes observed by Pettersson 

 agree very closely with those calculated for a water con- 

 taining 7 parts of chlorine in a million. 



The irregularities in the melting-points of bodies like 

 acetic acid, to which Pettersson refers, are without doubt 

 due to a perfectly similar cause. 



Also the very low latent heat observed by Pettersson 

 for sea-water is to be explained by the fact that the salt 

 retains a considerable proportion of the water in the 

 liquid state even at temperatures many degrees below the 

 freezing-point of distilled water. 



The plasticity of ice and the motion of glaciers receive 

 a simple and natural explanation when we see, as in 

 Table III., that, if the water from which this ice is pro- 

 duced contains no more than 7 parts of chlorine per 

 million, it will, in the process of thawing, when the tem- 

 perature has risen to -o''07 C, consist to the extent of 

 I per cent of its mass of liquid brine or water. The 

 water considered in Table III. is certainly not less free 

 from foreign ingredients than rain or snow. It follows, 

 therefore, that a glacier, in a climate where the tempera- 

 ture is for the greater part of the year above o' C, must 

 have a tendency tofiow, owing to the power of saline solu- 

 tions to deposit ice and to dissolve it at temperatures 

 below o^ C. 



( To be continued.) 



NOTES 

 The Endowed Schools Committee, of which Sir Lyon Playfair 

 is Chairman, after sitting for a year and a half, have agreed to 

 their Report. This is not yet issued, but it is known that the 

 Committee have reported in favour of endowed schools being 

 in future largely used for the promotion of scientific and 

 technical education. The Report also recommends that local 

 authorities should be authorised to employ local rates for found- 

 ing or contributing to laboratories and workshops in such schools 

 in order to promote practical scientific education. 



L.\ST week an important Conference was held at Oxford for 

 the consideration of questions connected with the University 

 Extension Scheme. The meetings were attended by many mem- 

 bers of the University, local delegates, and others interested in 



