490 Mr. Pickering on the Theory of Osmotic Pressure 



but here, as in all the above cases, the catalytic agent, by 

 producing a condition of dynamical equilibrium, greatly 

 facilitates the change. 



Further instances of the precise similarity between the 

 action of catalytic agents and of those substances which are 

 capable of endowing nonconducting liquids with the power of 

 conduction will doubtless be found, and further proof analo- 

 gous to those advanced here in the case of stannic chloride of 

 the strict parallelism between the phenomena, of the birth of 

 electrolytic power and of enhanced chemical activity, will 

 trace these effects back to an identity of cause, the setting up 

 of a condition of dynamical equilibrium. 



Emmanuel College, Cambridge. 



LVI. The Theory of Osmotic Pressure and its bearing on the 

 Nature of Solutions. By Spencer Umfrevillb Pickering, 

 M.A* 



TVTO one can doubt the mathematical correctness of the 

 -L ^ conclusions which Arrhenius/van't Hoff, Ostwald, and 

 others draw from the premisses with which they start in their 

 arguments respecting osmotic pressure, nor can we doubt the 

 value of connecting numerous actions with one and the same 

 cause, or that there are a large number of instances in which 

 the observed facts are in substantial agreement with their 

 conclusions. But we may, I think, legitimately doubt 

 whether the premisses of the arguments are sound, whether 

 the conclusions harmonize as well as they should with ex- 

 perimental data, whether the theory is more than a mathe- 

 matical exercise, or more than a convenient working hypo- 

 thesis of a rough character, instead of being, as its supporters 

 maintain, an hypothesis established so firmly that we may 

 build upon it a physical theory of solution. 



The direct measurement of osmotic pressure has been made 

 in but a few cases, and those cases are ones in which the 

 substances examined are eminently unfitted for showing the 

 presence of any chemical action which may be present. Of 

 the phenomena correlated with osmotic pressure, the lowering 

 of the freezing-point of a solvent by the addition of foreign 

 substances is the one which has received the greatest atten- 

 tion, thanks to Raoult's classical work, and is the one which 

 forms the main support of the theory. 



In examining the experimental facts the following ques- 

 tions must be asked, and if the theory is correct they must be 

 answered in the affirmative. 



* Communicated by the Physical Society : read March 7, 1890. 



