214 Prof. L. Kahlenberg on the 



people who have not yet surmounted all its difficulties nor 

 forgotten the hard labour they went through in mastering 

 the rudiments of it, should discuss just such points as are 

 brought out so interestingly in the paper by Professor Orr 

 which was the stimulus for the foregoing remarks. 



Washington, D.C., U.S. Dept. of Agriculture, 

 November 1, 1904. 



XXI. Recent Investigations bearing on the Theory of Electro- 

 lytic Dissociation. By Louis Kahlenbekg, Ph.D., Pro- 

 fessor of Physical Chemistry in the University of Wisconsin*. 



IN creating the theory of electrolytic dissociation the phe- 

 nomena of actual electrolysis have played a minor part. 

 The changes of concentration of the electrolyte around the 

 electrodes, the elevation of the temperature observed during 

 the passage of the current, and the fact that when polariza- 

 tion is prevented, electrolytes obey Ohm's law, were all 

 explained many years before the existence of the theory of 

 electrolytic dissociation. Indeed, the hypothesis of Clausius. 

 which displaced the old Grotthus theory and brought concep- 

 tions of electrolysis into harmony with thermodynamic re- 

 quirements, is by many chemists and physicists still regarded 

 as the best mechanical explanation of the electrolytic process, 

 when all facts are fully considered. 



Briefly stated, the theory of electrolytic dissociation is 

 based upon the observation that for a goodly number of 

 aqueous conducting solutions the so-called molecular conduc- 

 tivity increases with the dilution ; that osmotic pressure, 

 lowering of the freezing-point, elevation of the boiling-point, 

 or lowering of the vapour-tension of such solutions is abnor- 

 mally great (i. e., that it is greater than for non-conducting- 

 solutions, the behaviour of which it is asserted conforms to 

 the requirements of the gas equation) ; and that the so-called 

 degree of electrolytic dissociation may be calculated from 

 the electrical conductivity of the solution or from its osmotic 

 pressure, its boiling-point, freezing-point, or vapour- tension. 

 Indeed, the dissociation hypothesis is vitally connected with 

 van't Hoff's theory of solution. The latter claims that dilute 

 solutions behave according to the equation PV = «RT, in 

 which the factor i is unity for non-electrolytes. The analogy 

 between a gas and a solution has been recognized so long 

 that it would be difficult to state when the idea originated ; 

 but van't Hoff, by using Pfeffer's direct measurements of 



* Communicated by the Faraday Society. Bead before the Society. 

 November 23, 1904. 



