148 Prof. Ostwald on Chemical Action at a Dista 



nee. 



phuric acid, goes into solution as sulphate. It is also known 

 that the solution of zinc and similar metals in dilute acids is 

 extremely accelerated by the presence of " electronegative " 

 metals, and the text-books with the mention of this fact do 

 not neglect to emphasize the " galvanic contrast" which con- 

 ditions the effect. Yet I do not know that an attempt at a 

 closer analysis has been made, an effort in the direction of an 

 explanation of the way in which the " galvanic contrast " can 

 produce such action. In fact these actions, like so many 

 others, seem to belong with those for which a satisfying 

 explanation can be first gained on the ground of the Theory 

 of free ions, of Arrhenius. They then assume the following 

 form. 



Assume a metal, as zinc, to be in contact with the solution 

 of an electrolyte, as potassium sulphate. The zinc may only 

 go into solution by its atoms becoming loosened from the 

 metal in the form of ions with their corresponding charges 

 of electricity. In what manner this charging with electricity 

 takes place, and in what it consists, are questions which we 

 cannot at present answer ; but since by taking positive elec- 

 tricity from the ions of the metals we can get the latter 

 with their familiar properties again, we are justified in looking 

 upon the taking up of positive electricity as the characteristic 

 of the transition of a metal into the condition of ions. 



As positive ions leave the originally neutral zinc, the latter 

 becomes charged negatively and the solution positively. This 

 lasts until a certain definite difference of potential has been 

 established between the metal and the solution, according to 

 which just as many positive ions are attracted out of the 

 solution by the negative charge of the metal, as go into the 

 solution as a result of the "solution-tension" of the zinc"*; 

 then equilibrium occurs. On account of the very great quan- 

 tities of electricity carried by the ions the necessary quantities 

 of metal are extremely slight, in general too slight to be 

 shown by analytical tests. 



The zinc is accordingly hindered from further solution by 

 the excess of positive ions which exists in the liquid, and in 

 order to make further solution possible these ions must be 

 removed. If another metal, for example platinum, be con- 

 nected with the zinc, this assumes the same negative charge 

 as the zinc. If the platinum be dipped into the liquid this 

 negative charge acts electrostatically upon the excess of 

 positive ions, and these collect at the platinum. 



Now the facts of galvanic polarization show that the elec- 



* Refer to W. Nernst, Zeitschrift fur physikalische Chemie, iv. p. 150 



(1889). 



