362 



SCIENCE. 



[N. S. Vol. XXIV. Ko. 612. 



'selective action of the membrane' and 'in- 

 sists 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. Whet- 

 ham, who, I confess, seems to me to be 

 capable of holding his own without need of 

 reinforcements. He has pointed out that 

 confusion has arisen from the use of the 

 term 'osmotic pressure' to denote the ac- 

 tual pressure experimentally realized in 

 certain conditions, as well as the ideal pres- 

 sure 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 con- 

 stant in dilute solutions and decrease slow- 

 ly with increasing concentration, while the 

 conductivity of a dilute solution is at most 

 proportional to the first power of the con- 

 centration, appears irreconcilable with any 

 assumption as to the existence of the active 

 part of an electrolyte in the form of com- 

 bined 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. 



Professor Armstrong remarks that it is 

 unfair to 'cloak the inquiry by restricting 

 it to thermodynamic reasoning, a favorite 

 maneuver with the mathematically mind- 

 ed.' 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 con- 

 fess that at one time I regarded the ex- 

 treme advocates of the theory of ionic dis- 

 sociation with a certain amount of suspi- 

 cion, but I think that most of those who 



have studied the evidence now at our dis- 

 posal, or who have been engaged in experi- 

 mental investigation into this interesting 

 branch of physics, can not 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 thermodynamic con- 

 siderations is justifiable, until we are pre- 

 sented with stronger arguments than those 

 based on the repulsiveness to certain chem- 

 ists 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 membranes. 



I will now trespass upon your forbear- 

 ance 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 consid- 

 erations, which naturally arise in any com- 

 parison 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 knowledge' 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 al- 

 though this accumulation is one which we 

 may well regard with satisfaction, it neces- 

 sarily gives rise to difiiculties unfelt by our 

 predecessors. 



I venture to indicate one of such difficul- 

 ties, one which has been brought home to 

 me both by my experience as an examiner 

 and by the fact that during the past few 

 years I have had to preside over many 



