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SCIENCE. 



[N. S. Vol. IV. No. 93. 



metal into ions in solution as soon as it is 

 immersed in an electrolyte; this has been 

 termed electrolytic solution tension. Os- 

 motic pressure and solution tension thus 

 become analogous concepts. Three condi- 

 tions are possible in the battery cell : 



1. If the solution tension be greater than 

 the osmotic pressure the metallic plate acts 

 like a salt mass in a dilute solution. Kath- 

 ions will be thrown into the solution posi- 

 tively charged, leaving an equal negative 

 charge upon the electrode ; at the surface of 

 separation between solution and electrode 

 we shall have positive kathions upon one 

 side and negatively charged metal upon the 

 other, these exerting electrical forces, a con- 

 dition will be reached when they are equal 

 to the solution tension, further action will 

 then cease until the kathions are discharged 

 or made metallic. 



2. If the osmotic and solution pressures 

 are equal, no difference in potential will 

 result ; as when a mass of salt is introduced 

 into a saturated solution, of itself no change 

 takes place in equilibrium. 



3. When the osmotic pressure is greater 

 than the solution tension, kathions will be 

 projected upon the plate and made metallic, 

 the electrode becoming positively charged 

 and the solution negatively, similar to the 

 action which takes place when a solid salt 

 is brought into contact with a supersatu- 

 rated solution where salt particles will be 

 deposited. 



The determination of the relative values 

 of solution pressures is comparatively sim- 

 ple, the determination of their absolute 

 values very difficult. In the case of mer- 

 cury and a saturated solution of calcium 

 chloride, the absolute value has been deter- 

 mined with considerable accuracy from the 

 effect upon tension phenomena in the mer- 

 cury surface, fully discussed by Lippman, 

 Helmholtz and Paschen. Ostwald and 

 Planke obtained, values by two methods 

 based upon this action agreeing very well. 



With this value as a basis others have been 

 determined. Applying those values experi- 

 mentally obtained, together with the ones 

 for osmotic pressure, in calculating the 

 electromotive force of a number of well- 

 known cells, an excellent agreement with 

 experimentally determined values is found. 



It will be impossible in this review to 

 apply these theories to the various forms of 

 batteries known, and to many phenomena 

 of electrolysis which we have no space even 

 to mention ; the theories briefly reviewed 

 have borne rich fruit in the more satisfac- 

 tory explanation of electrolytic action. 

 Many problems still remain to be attacked, 

 while some have been but now appreciated. 



The development of the solution and 

 dissociation theories gives no explanation 

 of the forces and conditions which cause 

 solution or ionization, though some attempts 

 have been made in this direction. Thus, 

 J. J. Thomson has shown that if the at- 

 tractions between the ions in the molecule 

 is due to electrical forces it will be weak- 

 ened, if the molecules be immersed in a 

 medium of high specific inductive capacity. 

 Experimental evidence, in so far as it goes, 

 shows that in liquids of high specific in- 

 ductive capacity, ionization is most com- 

 plete. This is one of the problems to be 

 systematically studied. 



With the solution of the older problems 

 new ones present themselves. This is the 

 effect of any comprehensive good theory. 

 Many new problems in molecular physics 

 and electrolysis are suggested through Ar- 

 rhenius's,Van't Hoft's and Nernst's theories. 

 Their development and solution will not be 

 one of chance, however, to be stumbled 

 upon by daring or blind groping, but by in- 

 telligent, painstaking research. A bird's- 

 eye view of the field is given us through 

 these theories, in filling in the detail and 

 contours, the chance explorer must give 

 way to the systematic investigator. 



Until within the last three or four years, 



