ÖFVERSIGT AF K. VETENSK.-AKAD. FÖRHANDLINGAR 18 94, N:0 2. 43 



must be referred to hydrogen is, that this gas is always present; 

 besides this it is evident, that if a metal is more positive than 

 hydrogen, the latter will be substituted by the former, partly 

 by reason of the presence of water and partly by the presence 

 of free acid. In this way the deposited metal becomes mixed 

 with oxides, while the liberated hydrogen unites with the metal. 

 These two circumstances are the two main reasons of spoungey 

 deposites. 



In order to foresay, to which of the two classes a metal 

 belongs, I have made the following experiment: 



A glass vessel was filled successively first with a normal 

 Solution of H0SO4, then with HCl and lastly with HNO3. A 

 glass tube, the end of which was drawn out to a capillary 

 point, was filled Avith diffierent salt solutions, so that the same 

 acid always existed in the glass tabe and in the vessel; on a 

 platinumplate was then deposited spoungey platinum from acidu- 

 lated PtCi^. This plate was coated electrolytically with hydrogen 

 by electrolysing Vio normal Solution of the acid, which for the 

 time being existed in the glass vessel. The glass tube and the 

 platinumplate were then placed in this vessel and the metal to 

 be examined was introduced in the tube. The experiment was so 

 arranged, that this metal always constituted the positive part of 

 the salt in the tube; the metal was then connected with one 

 poole of a condensator, while the other was connected with the 

 platinumplate. The condensator was then discharged through 

 a Thomson galvanometer. The platinumplate was coated with 

 hydrogen with a density of current of 1,6 ampere per cm- 

 during a time of three rainutes and three minutes after the charge 

 the galvanometer was observed. The examined metal was 

 thoroughly cleaned immediately before each experiment. 



The following table gives the result; whether a metal is 

 more or less positive as against hydrogen is indicated by + 

 and — in the last column: 



