viii EFFECT OF ALTERING ELECTRICAL TENSIONS 277 



positive hydrogen - ions, travelling much faster than the negative 

 chlorine-ions, 1 will diffuse more quickly into the surrounding water, 

 and, carrying their positive charge with them, render the region of the 

 water where they arrive more positive than that part containing the 

 slowly wandering chlorine ions. If one electrode is placed where the 

 hydrogen-ions are abundant and another one where the chlorine-ions 

 were left behind, an electrical current can be readily demonstrated. 2 

 Similarly, if we start with a liquid chain composed, for example, of 5 

 molecular per cent sodium chloride solutions at the ends and 10 

 molecular per cent hydrochloric and 1 molecular per cent caustic soda 

 in the middle, 



"l 



then by the interaction of the alkali and the acid a 5 molecular per 

 cent salt solution will be formed in the middle : 



On diluting A and E a current will pass from B to D, that is, from the 

 alkali to the acid, because the hydrogen-ions, H, will pass from D into 

 E more quickly than the chlorine-ions, Cl', and similarly the hydroxyl- 

 ions, GET, enter A more freely than do the slower ions ; therefore an 

 excess of negative chlorine-ions being left in D and an excess of posi- 

 tive sodium-ions in B, the latter becomes electro-positive to D and the 

 current in the solution passes from B to D. 



The same result will be obtained by strengthening the salt solution 

 in C, and for the same reason. 



On strengthening the salt solutions in A and E, or by diluting the 

 salt solution in C, a current will be set up from the acid to the alkali, 

 from D to B, because the fast hydrogen-ions will carry their positive 

 charges from D to C at a quicker rate than do the slower hydroxyl- 

 ions carry their charge from B to C. When the hydrogen-ions meet 

 the hydroxyl-ions, neutral water is formed, but there being, owing to 

 the rate of migration, more hydrogen-ions than hydroxyl-ions, a posi- 

 tive stream is set up from D to B. 3 



Should precipitates be formed which do not act as conductors, such 



1 Hydrogen-ion = 320 ; OH-ion = l74; chlorine-ion = 65 ; K-ion = 65; Na-ion = 44. 



2 The idea that differences of potential are due to differences in the rate of migration 

 of ions was first suggested by Nernst, 1888. 



3 Worm-Muller, Poggendor/" s Annalen, 104, 114 (1870). See also Max Oker 

 Blom, Pflagers Arch. 84. 191 (1901), 85. 543 (1901). 



