150 Prof. Ostwald on Chemical Action at a Distance. 



la Eive ; well amalgamated zinc has the same property. The 

 metal does not have, in this case, less tendency to go into 

 solution than when impure ; for if it be connected with pla- 

 tinum, copper, or any other similarly acting metal, solution 

 at once ensues. The difficulty lies, therefore, plainly not in 

 the dissolving of the zinc, but in the evolution of the hydrogen; 

 when this latter action is assisted the solution takes place, in 

 the case of either pure or amalgamated metal. That the 

 hydrogen is evolved with difficulty at the zinc, more readily 

 at the so-called negative metals, lies in the differences of 

 potential towards the electrolyte. Zinc has a strong, positive 

 solution-tension, that is it sends positive ions readily into 

 the liquid and opposes correspondingly the reverse action, 

 the reception of positive hydrogen ions and the removal of 

 their charges. The other metals in contact with the same 

 electrolyte develop a far less difference of potential, or pos- 

 sibly one of opposite sign, and either offer far less resistance 

 to the discharging of the hydrogen or even assist it. 



This is the reason why zinc dissolves in acids when in con- 

 tact with other metals ; it is clear that the usual form of 

 expression, that solution takes place in consequence of galvanic 

 currents between the zinc and the other metals, does not 

 entirely correspond to the facts of the case. The galvanic 

 currents are indeed inseparably connected with the act of 

 solution ; they are, however, not the primary agent which 

 effects solution, but are produced by the act of solution which 

 they must necessarily accompany, because the question is one 

 of the formation and displacement of ions. Solution ensues 

 when the possibility is present that the positive ions in the 

 solvent may in any way be removed therefrom. 



Differing from the simple displacement of positive ions, as 

 in the case of zinc (as also magnesium, cadmium, and a 

 few other metals), the dissolving of such metals as are not 

 able to effect this displacement is accomplished by means of 

 the destruction of positive ions, or what has the same effect, 

 the creation of negative ions. Both are accomplished by the 

 action of oxidizing agents, the first by means of reactions 

 which produce non-electrolytes, the second by such as produce 

 electrolytes. 



An example of the first case is the dissolving of copper in 

 dilute sulphuric acid, which takes place slowly under the 

 action of free oxygen. Here the hydrogen ions of the acid 

 combine with the oxygen atoms to form the non-electrolyte 

 water, and thereby it becomes possible for a corresponding 

 number of copper ions to be formed, that is for the copper to 

 go into solution. 



