146 Prof. Ostwald on Chemical Action at a Distance. 



is rapidly dissolved, on the contrary, with evolution of hy- 

 drogen, when the liquid about the platinum is acidified. The 

 hydrogen appears on the platinum, as it always does when 

 these two metals are in contact. In order, under the de- 

 scribed conditions, to bring the zinc into solution, the solvent 

 must be allowed to act, not upon the metal to be dissolved, 

 but upon the platinum which is connected with it. 



Zinc behaves in a solution of common salt in exactly the 

 same way as in one of potassium sulphate ; cadmium shows 

 the same behaviour. Tin is quite easily dissolved in a solu- 

 tion of common salt when the metal is connected with platinum 

 and the liquid about the latter is acidified. Yet in a solution 

 of potassium sulphate, tin armed with platinum is dissolved, 

 even with the aid of sulphuric acid, but very slowly, just as 

 this metal alone is attacked only in slight degree by dilute 

 sulphuric acid. The behaviour of aluminium is similar to 

 that of tin ; yet the experiments therewith are not so striking, 

 because with a neutral solution of common salt it develops 

 bubbles of hydrogen upon its own surface (which is pre- 

 sumably to be referred to the carbon contained in the metal) ; 

 still, at least, solution takes place far more rapidly when the 

 solution of salt is acidified at the platinum. In potassium 

 sulphate also there ensues almost no solution upon acidifying 

 at the platinum, just as dilute sulphuric acid scarcely acts 

 upon aluminium. 



The phenomena described agree in this, that the metals in 

 question when brought, in contact with platinum, into neutral 

 salt-solutions, are dissolved when the ordinary solvents of 

 these metals are allowed to act upon the platinum. It may 

 be asked whether the metals which are dissolved, not with 

 evolution of hydrogen, but only with the accompanying action 

 of an oxidizing agent, may be brought into solution according 

 to the same fundamental principle. Experiment answers this 

 question affirmatively ; even the more resisting metals, when 

 connected with platinum, upon which their specific solvent is 

 allowed to act, are dissolved in liquids which otherwise never 

 attack them. 



So, for instance, after a few minutes one finds considerable 

 amounts of silver dissolved in dilute sulphuric acid, when the 

 metal has been connected with a platinum wire near which a 

 few drops of chromic-acid (or potassium-bichromate) solution 

 have been added to the sulphuric acid. At the same time 

 every caution may be employed to protect the silver from 

 contact with the chromate, and yet the action will be found : 

 the experiment decides unequivocally that the contact of the 

 platinum with the oxidizing agent conditions the dissolving 



