198 



HYDROGEN ION CONCENTRATION 



troljd^ic conductivity in which ionic transport was involved. For 

 E. Warburg^ had abeady shown that at 200°C the conductivity 

 of glass was of electrolytic nature, and undoubtedly Cremer was 

 justified in interpreting the conductivity of much thinner glass 

 walls as being of electrolytic nature. Cremer made the striking 

 observation, which was not appreciated until much later, that an 

 aqueous acid solution inside of his thin glass bulb showed a poten- 

 tial difference of about one volt towards an alkaline solution outside 

 of the bulb (the value observed was 0.55 volts, to which a correction 

 for the diffusion potential had to be added). Cremer recognized 

 the glass wall as the source of this electromotive force, and he also 

 quite correctly recognized the great significance of the acidity of 



the solution in determining the value 

 of this E.M.F. But his interpretation 

 is somewhat different from that given 

 later by Haber. 



Haber and Klemensiewicz^ were the 

 first to advance the theory which is still 

 held today, and they made exact meas- 

 urements and extensive application of 

 the glass chain. When two solutions 

 of unequal hydrion concentration are 

 separated by an extremely thin glass wall, 

 a potential difference arises between the 

 two solutions which is of the same mag- 

 nitude as that developed in a hydrogen 

 gas chain as described on page 161. The arrangement of the glass 

 chain is as shown in figure 25. 



The solution of hydrion concentration h2 is placed in a large beaker 

 the solution of hydrion concentration hi is in a very thin walled 

 glass bulb which is immersed into the first solution. The current is 

 led away on one side by means of a calomel electrode and on the 

 other by a platinum wire (instead of the latter it would be better 

 to use a calomel electrode also, in order that the two electrode poten- 

 tials compensate each other). E is an electrometer, best of all a 

 binant electrometer. If in a series of experiments the inner solu- 

 tion be kept constant and the outer solution varied, we find for a 



^ Cited by Georg Meyer, Wiedemanns Ann. 40, 244 (1890). 



« F. Haber and Klemensiewicz, Ann. d. Physik [4] 26, 927 (1908) 



Fig. 25. Glass-chain 



