{6o 



NA rURE 



[August 9, 1906 



of opposite errors of a very improbable nature, it is 

 diflicuit to imagine a more direct vindication of llie ap- 

 plication of thermodynamic considerations to the pheno- 

 mena of solution. I may add that I also examined corre- 

 spondingly dilute solutions of sodium chloride, barium 

 chloride, sulphuric acid, potassium bichromate, magnesium 

 chloride, and potassium iodide ; but, owing to the circum- 

 stances to which I have referred, I was unable to repeat 

 these experiments in such a manner as to enable me to 

 attach great importance to the resulting figures. Never- 

 theless, I obtained values which strengthened the con- 

 clusions to which I was led by the more exhaustive examin- 

 ation of the dilute solutions of sugar and potassium chloride. 



So far back as the Liverpool Meeting of this Associa- 

 tion I expressed a hope that the experimental difficulties 

 of the direct measurement of osmotic pressures would be 

 overcome, as such direct measurement would afford the 

 most useful data by means of which to obtain further light 

 on the much-vexed question of the nature of solutions. I 

 remember, also, that it was the general opinion of those 

 who had given attention to this matter that the experi- 

 mental difficulties were insuperable. 



I am glad, therefore, to have this opportunity of staling 

 my high appreciation of the inanner in which Lord 

 Berkeley and Mr. Hartley have grappled with the diffi- 

 culties of this investigation. They have proved that the 

 osmotic pressure obtained by direct measurement agrees 

 with that derived from vapour-pressure observations to 

 within less than 5 per cent.' The agreement is of great 

 importance, as it diminishes our doubts as to the extent to 

 which the imperfections of semi-permeable membranes may 

 affect the validity of results dependent upon their behaviour, 

 and points to the possibility of determining the osmotic 

 pressures of concentrated solutions by measurement of their 

 vapour pressures. 



I trust it will not be thought out of place if I here 

 refer to the interesting correspondence which has recently 

 appeared in Naiure on the thermodynamic theory of 

 osmotic pressure, and the allied, but by no means identical, 

 problem of the difference between electrolytic and non- 

 electrolytic solutions. 



On the one side we have Prof. Armstrong, whose 

 chief desire appears to be the vindication of the moral 

 character of what he terms "the poor molecule"; and 

 Mr. Campbell, whose doubts concerning the second law 

 of thermodynamics are closely connected with a lurking 

 belief in the existence of Maxwell's "sorting demons"; 

 and by way of reserves we have Prof. Kahlenberg, who 

 contends that " thermodynamic reasoning cannot be applied 

 to actual osmotic processes " on account of the " selective 

 action of the membrane " and " insists that the formation 

 of crystals from a solution or the concentration of a solution 

 by evaporation are not osmotic processes." 



On the other hand we have Mr. Whetham, who, I con- 

 fess, seems to me to be capable of holding his own with- 

 out need of reinforcements. He has pointed out that con- 

 fusion has arisen from the use of the term " osmotic 

 pressure " to denote the actual pressure experimentally 

 realised in certain conditions, as well as the ideal pressure 

 required in thermodynamic theory. With regard to the 

 theory of electrolytic dissociation, Mr. Whetham shows that 

 the fact that the velocities of the ions are constant in dilute 

 solutions and decrease slowly with increasing concentration, 

 while the conductivity of a dilute solution is at most pro- 

 portional to the first power of the concentration, appears 

 irreconcilable with any assumption as to the existence of 

 the active part of an electrolyte in the form of combined 

 molecules when in solution. I would here join with Mr. 

 Whetham in the request that those who oppose the theory 

 of ionic dissociation would state their views as to the 

 mechanism of electrolysis, and their reasons for supposing 

 that the application of the principles of thermodynamics to 

 the phenomena of solution is unjustifiable. 



Prof. Armstrong remarks that it is unfair to " cloak 



540 grains per lit. solu 



tO.P. ; 

 67'5 



NO. IQI9, VOL. 74] 



O.P. deduced 



from vapour 



pressure at o" C. 



69-4 



•B . . . IOI-9 

 7 . . . T36-0 

 Proc. Roy. See, June, 1906. 



the inquiry by restricting it to thermodynamic reasoning, a 

 favourite manccuvre with the mathematically minded." He 

 adds that such a course may satisfy the physicist, but " is 

 repulsive to the chemist." 



The inquiry, " Why is the application of thermodynamic 

 reasoning repulsive to the chemist?" naturally suggests 

 itself. I confess that at one time I regarded the extreme- 

 advocates of the theory of ionic dissociation with a certain 

 amount of suspicion, but I think that most of those who 

 have studied the evidence now at our disposal, or who have 

 been engaged in experimental investigation into this inter- 

 esting branch of physics, cannot fail to agree with Mr. 

 Whetham that, as regards the fundamental conceptions of 

 the theory, " the cumulative evidence seems overpowering." 

 At all events, we may consider that the application to the 

 phenomena of solution of reasoning based on thermodynamii 

 considerations is justifiable, until we are presented with 

 stronger arguments than those based on the repulsiveness 

 to certain chemists of the conclusions to which it leads, or 

 the doubt it throws upon the activities of Maxwell's 

 demons and the selective action of semi-permeable mem- 

 branes. 



I will now trespass upon your forbearance and pass from 

 the consideration of such special departments of natural 

 science as usually engage the attention of members of 

 this Section to some more general considerations, which 

 naturally arise in any comparison of our knowledge of to- 

 day with that which we possessed when we last met in 

 this city. 



It will, I think, generally be admitted that during the 

 last twenty-five years the increase in our " natural know- 

 ledge " has been greater than in any previous quarter of 

 a century. 



Day by day we are adding new facts to our storehouse 

 of information, until it has now become impossible for 

 the individual to have more than a superficial knowledge 

 of the contents of the building. And although this accumu- 

 lation is one which we may well regard with satisfaction, 

 it necessarily gives rise to diflficulties unfelt by our pre- 

 decessors. 



I venture to indicate one of such difficulties, one 

 which has been brought home to ine both by my experience 

 as an examiner and by the fact that during the past few 

 years I have had to preside over many meetings of 

 examiners, and to mark the effect of examinations on the 

 teaching in our universities. 



We now expect a student to acquire in a three years' 

 course a far greater amount of information than was con- 

 sidered necessary, say, twenty-five years ago. The atten- 

 tion both of the teacher and of the taught is naturally 

 directed to those extremities of the branches of science in 

 which the growth has been most marked in recent years, 

 and I venture to think that there is in consequence some 

 danger of our neglecting the roots of the whole matter. 

 Compare, for example, a Final paper in chemistry in any 

 one of our universities with its predecessor of a quarter 

 of a century ago. 



The enormous advance of organic chemistry has neces- 

 sarily reacted on the examinations, and thus the student 

 Is unable to devote an adequate proportion of his time 

 and attention to the foundations of the subject. The same 

 remark applies in the domain of physics. There is a 

 danger, therefore, of our educational edifice becoming top- 

 heavy. 



I have heard complaints, on the one hand, from the 

 examiners that while the candidates frequently exhibit 

 considerable knowledge of the most recent scientific develop- 

 ments, thoy show a lamentable ignorance of the simple 

 phenomena and the principles they illustrate. On the other 

 hand, I have heard from candidates that many of the ques- 

 tions were too simple — that they were concerned with 

 principles and facts to which their attention had not been 

 directed since they first began the studv of natur.al science. 



My own experience has been that the simplest questions 

 are those answered in the least effective manner. A candi- 

 date unable to give satisfactory illustrations of Newton's 

 Laws will discourse upon the mass of an electron or the 

 nature of the Rontgen rays, and attempt the solution of 

 problems on such subjects as Hertzian waves and electric 

 convection. 



