June 8, 1916] 



NATURE 



301 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Molecular Attractions in Solutions. 



The following is, so far as I know, a new method 

 of attacking this problem. I have been working at 

 the experiments for some time, but on account of the 

 war progress in the matter has come almost to a 

 standstill. It seems desirable to publish this brief 

 preliminary note now. 



Let A and B be two pure liquids miscible (com- 

 pletely miscible would be better still) over a large 

 range of concentrations. Let the densities and com- 

 pressibilities of the liquids and their mixtures be 

 known. Then, taking the simplest case {i.e. one in 

 which there is no association either in the mixture or in 

 the pure liquids), we may postulate that if there be a 

 change in volume on mixing, this change is caused 

 by the algebraic sum of the alterations in the attrac- 

 tions of A to A and B to B, together with the added 

 effect of the new attractions of A to B. 



The sum of these three effects can be calculated 

 with considerable plausibility. Consider any definite 

 mixture, the coefficient of compressibility of this mix- 

 ture being supposed known over a wide range of 

 pressure. As we know the coefificient for the separate 

 pure liquids, we could calculate the theoretical co- 

 efficient of the combination. From these data we can 

 get an approximate value for the mean coefficient of 

 compressibility of the mixture while passing, so to 

 speak, from the theoretical combined state to that 

 which ultimately prevails. Then the change in volume 

 divided by this mean coefficient gives the change of 

 internal pressure on mixing. Now, if this method be 

 followed by a number of different concentrations, a 

 series of different changes in internal pressures will 

 result. 



If it is desired to disentangle the various internal 

 attractions from one another, this can only be done 

 by trial and error. The following development of 

 Laplace's method may be tried. Assume that the 

 attractions are proportional to the mass of the opera- 

 tive particles, then, calling the changes of pressure 

 P,, P2, etc., and referring the concentrations to a 

 gram-mol. of liquid A, let V be the volume of the 

 mixture which contains i gram-mol. of A, and n the 

 accompanying mass of component B. 



The change of attraction of A to A In mixture (i) 

 will be proportionate to o/V,^. 



The change of attraction of B to B in mixture (i) 

 will be proportionate to j8n,*/V,'. 



The change of attraction of A to B in mixture (i) 

 will be proportionate to niy/Vj*. 



From these quantities we get a set of equations : — 



P2 = (o + n.y + ^n,«)/Vj», etc., 



where o, P, and y are algebraic quantities. 



There are some reasons for supposing that y may 

 be equal to (a/3)i ; if so, a and ^ can be calculated from 

 any two of the equations, when P,, n,, etc., are 

 known, and hence the validity of the assumption may 

 be tested over any range of concentrations. Obviously 

 a formula of this type would not meet the case in 

 which the two liquids can mix in all proportions with- 

 out change of volume; but it is possible that although 

 the total pressure now remains constant, yet there 

 may have been a redistribution of pressure among the 

 constituents. 



NO. 2432, VOL. 97] 



It may be mentioned that even an empirical formula 

 giving appro.ximate values for the separate internal 

 pressures would be of considerable help in deducing a 

 correct equation of state for the osmotic pressures of 

 solutions. Berkeley. 



Foxcombe, May 24. 



Meteorological Conditions of a Blizzard. 



As used to signify a certain type of snowstorm 

 primarily characterised by fine, dry, powdery, or 

 sand-like snow driven before a gale of wind, the tem- 

 perature of which is extremely low (say 20° below 

 zero F.), the term " blizzard " is, of course, wholly 

 inapplicable in the British Isles ; and it is, moreover, 

 ridiculous to apply the name to every little occurrence 

 of sleet after the manner of the daily Press, referred 

 to by Mr. Dines. But there is another type of severe 

 snowstorm peculiar to damp, stormy, and relatively 

 warm winter climates like our own, the natural breed- 

 ing-grounds of which are the wild tracts of bleak, 

 elevated moorland which cover so much of the north 

 of England and Scotland; and I fail to see why 

 "blizzard," which, after all, comes from the same 

 root as "blast," should not be as expressive of a 

 British moorland snow gale, with its relatively large 

 ^amp flakes, as it is of the fine dry crjstals of North 

 America or the polar regions, produced by meteoro- 

 logical conditions practically unknown in this country. 

 The huge falls of snow swept by heavy gales which 

 isolated many high-lying districts of Great Britain 

 for weeks together in February and March of the pre- 

 sent year (see Symons's Meteorological Magazine for 

 April), bringing in a few weeks an aggregate depth 

 of some 10 ft. to the Black Mountains in South Wales, 

 were, it seems to me, not inappropriately described as 

 "blizzards"; but for the sake of distinction it might 

 be advisable to restrict the use of the term to the 

 American type of storm. 



Mr. Dines refers to January 18, 1881, as affording 



the nearest approach to an American blizzard in the 



S.E. of England; but possibly an even better approxi- 



I mation was the great storm of March 9-13, 1891, in 



I the S.W. of England. In Devon and Cornwall the 



I " great blizzard " of that spring is now a household 



i word, and I do not think that anyone who either 



j experienced that west-countr\- visitation or has read 



j the vivid narratives regarding its effects will feel 



inclined to quarrel with the designation. 



L. C. W. BON.ACINA. 



Hampstead, N.W., June 2. 



SIR ERNEST SHACKLETON'S ANTARCTIC 

 EXPEDITION. 



OIR ERNEST SHACKLETON has fully 

 ^ justified the faith of those who were con- 

 fident that if he did not cross Antarctica his ex- 

 pedition would make valuable additions to the 

 geography of the little-known area of the Weddell 

 Sea and that he would act with the combined 

 daring and sound judgment necessary to success 

 in what was admittedly almost a geographical 

 forlorn hope. He is to be congratulated on his 

 return after one of the most adventurous of Polar 

 expeditions; for its voyage on the ice-floes has 

 been only equalled in perils by that of the Hansa 

 Expedition ; his heroic passage in search of 

 help across the stormy seas south-east of Cape 

 Horn during an Antarctic winter will rank among 

 the finest examples of seamanship achieved in 

 an ordinary ship's boat; and, having landed on 



