296 



NATURE 



[August 31, 1911 



ion as in the observatory. But I often think that the 

 recognition of new events is scarcely given its proper place 

 in the annals of science if we have due regard to the 

 consequences. I have protested that in much of his work 

 the observer cannot be judged by the fruits of his labour, 

 though there is an instinctive tendency to judge in this 

 way ; but here is a case where he might well be content 

 to be so judged, and yet the consistent award is with- 

 held. Think for a moment of the very considerable addi- 

 tions to our knowledge which have accrued from the dis- 

 covery by Prof. W. H. Pickering of an Eighth Satellite to 

 Saturn. The discovery led directly to the recognition of 

 the retrograde motion ; and to explain this we were led 

 to revise completely our views of the past history of the 

 Solar system. Incidentally, it stimulated the search for 

 other new satellites, resulting in the discovery of a curious 

 pair to Jupiter, and next of the extraordinary Eighth 

 Satellite ; while it was the investigation of the orbit of 

 this curiosity which suggested an eminently successful 

 method of work on Cometary orbits. If we judge scien- 

 tific work by its results, we must take into account all 

 this subsequent history in our appreciation of Prof. Picker- 

 ing's achievement. But whether we do so or not is prob- 

 ably a matter of indifference to him, for the true observer 

 is, above all things, an amateur, using the word in that 

 splendid sense to which Prof. Hale recently introduced us. 

 There have been many attempts to define an amateur. 

 One was given by Prof. Schuster in his eloquent address 

 to this Section at Edinburgh in 1892 : — 



" We may perhaps best define an amateur as one who 

 learns his science as he wants it and when he wants it. 

 I should call Faraday an amateur." 



We need not quarrel with his definition, and certainly 

 not with the noble instance with which he points it. But 

 after all I prefer the definition of Prof. Hale • :— 



" According to my view, the amateur is the man who 

 works in astronomy because he cannot help it, because he 

 would rather do such work than anything else in the 

 world, and who therefore cares little for hampering tradi- 

 tions or for difficulties of any kind." 



The wholly satisfactory nature of this view is that it 

 provides not only a definition, but an ambition and a 

 criterion. We feel at once the ambition to become 

 amateurs, for I deny stoutly that the distinction is con- 

 ferred at birth : it comes with work of the right kind. 

 And we may know what is work of the right kind by this, 

 if by nothing else : that by diligently performing it we 

 shall become amateurs who find it impossible to stop : 

 " who work in astronomy because we cannot help it." 

 Before an army of such men even the vast hordes of duskv 

 possibilities of which we are beginning to catch glimpses 

 must yield. The fight mav seem, and no doubt is, with- 

 out end ; and the opportunities for glorious deeds by which 

 outlying whole troops of the enemy are demolished'at once 

 are becoming rarer. We are confronted with the necessity 

 of attacking each possibility singly which threatens the 

 stopping of the conflict through sheer wpariness. Clearlv 

 the army of amateurs is the right one for the work ; weari- 

 ness cannot touch them : they will go on fighting auto- 

 matically because " they cannot help it." 



SECTION B. 



CHEMISTRY. 



Opening Address by Prof. J. Walker, D.Sc, F.R.S., 

 President of the Se< nox. 



Theories of Solutions. 



Twenty-one years ago the Chemistry Section of the 



British Association at its meeting in Leeds was the scene 



of a great discussion on the nature of solutions. It was 

 my first experience of a British Association meeting, and 

 I well remember the stimulating effect of the lively discus- 

 sion on all who took part in it. To-day. speaking from tin- 

 honourable position of President of the Section, I conceive 

 I can do no better than indicate the position of the question 

 at the present time. And this appears to me the more 

 1 Monthly Notices R.A.S., lxviii., p. 64. 



NO. 2183, VOL. 87] 



appropriate .1- our science has had this year to mourn the 

 departure of van 1 Hoff, the founder of the modern theory 

 of solution, whose name will remain one of the go 

 in theoretical chemistry — in time to come, it will, I think, 

 be considered almost the greatest. He had expressed the 

 hope that he might attend this meeting as he did that 

 twenty-one years ago. The hope is not fulfilled : his activity 

 is merged in the final equilibrium of death. But his ideas 

 are part and parcel ol the chemical equipment of every one 

 of us, and we know that whatever form the fundamental 

 conceptions of chemistry may assume, the quantitativ 

 of osmotic pressure will be to the theory of solution what 

 the quantitative idea of the atom is to chemical composition 

 and properties. For 1 must emphasise the fact that 

 chemistry is essentially a quantitative science, and no 

 chemical theory, no partial chemical theory even, can be 

 successful unless its character is quantitative. To quote 

 the words of Lord Kelvin : " I often say that when you 

 can measure what you are speaking about, and express it 

 in numbers, you know something about it ; but when you 

 cannot measure it, when you cannot express it in nun 

 your knowledge is of a meagre and unsatisfactory kind; it 

 may be the beginning of knowledge, but you have scarcely 

 in your thoughts advanced to the stage of science." 



A general theory of solutions must be applicable to all 

 solutions — to those in which solvent and solute exist in 

 practically mere intermixture, as well as to those in which 

 solute and solvent are bound together in what we cannot 

 sharply distinguish from ordinary chemical union. Between 

 these extremes all grades of binding between solvent and 

 solute exist, and it may be well to give a few examples 

 illustrating the various types of solution. 



Where no affinity exists between solvent and solute, the 

 solution is practically of the same type as a mixture of 

 two gases which are without chemical action on each other. 

 The solute is merely diluted by the solvent and retains its 

 properties unchanged. An example of this type of solution 

 may be found in the solution of one saturated hydrocarbon 

 in another, say of pentane in hexane. On mixing the two 

 liquids there is no evidence of union between them, the 

 volume of the mixture is practically the sum of the volume 

 of the components, the heat of solution is practically 111/, 

 the vapour pressure of each constituent is reduced n 

 as if by dilution with the other constituent, and so on. 

 That there is some action between the two components even 

 in this extreme case must be admitted, but it may be re- 

 ferred entirely to action of a physical kind, such as one 

 finds on mixing one gas with another at considerable 

 pressures. Action of a chemical nature is absent. If it be 

 said that even saturated hydrocarbons have some chemical 

 affinity for each other, recourse may still be had for 

 examples to mixtures of two inactive elements, say liquid 

 argon and liquid krypton, where chemical affinity is non- 

 existent. 



At the other extreme we have such solutions as those of 

 sulphuric acid and water. Here there is every physical 

 evidence of chemical union. The volume of the mixture 

 is by no means the sum of the volumes of the components, 

 the amount of heat evolved on mixing is very great, the 

 separate liquids, which are practically non-conductors, yield 

 on mixing a solution which is a good conductor, and so on. 

 There is obviously here a great influence of the solvent water 

 on the solute sulphuric acid, and this influence we can only 

 account for by assuming that it is essentially chemical in 

 character. 



As the influence in such a case is necessarily reciprocal, 

 then if even on.- of the constituents of the solution is inai tivi 

 chemically there can plainly be no action of a chemical 

 nature on mixing. Thus, no matter what solvent we take, 

 it can exercise no action other than that of a physical kind 

 on argon, say, which has been dissolved in it; and, again, 

 if liquid argon i< chosen as solvent no substance dissolved 

 in it can 1" affei ted by it chemically, and we thus obtain 

 only the properties of a physical mixture. It is convenient 



theref to classify liquid solvents according to their 



chemical activity. The saturated hydrocarbons, which are 

 chemically very inert, and, as their name paraffin implies, 

 little disposed to 1 Hi mical action of any kind, may lie taken 

 as typically inactive solvents, analogous to liquid argon. 

 Water, on the other hand, as its numerous compounds 

 (hydrates) with all kinds of substances testify, may be taken 



