40 CASSEL, ELECTROLYTICALLY DEPOSITED METALS. 



lysis. In many cases there are more than one salt in Solution 

 and consequently there are often a nuraber of diflferent ions siniul- 

 taniously present at the cathode. By reason of these facts it 

 inust be of importance to determine which of the ions are depo- 

 sited first and niostly. / 



Former authors have advanced tlie theory, that those sub- 

 stances are chiefly decomposed, who absorbe the least energie, 

 and this opinion was made plausible by referring to the fact, 

 that the least positive metal always appeared as the end-product. 

 This circumstance depends however on purely secundary and 

 chemical processes. 



Other authors considered that the current is trans'mitted 

 exclusively by one of the substances present in the Solution. ^) 



The latest researches on this subject have by Arrhenii dis- 

 sociation theory come to quite a different result. When the current 

 can be transmitted only by the dissociated molecules or the ions, 2) 

 the relative amount of the primary deposited ions must be pro- 

 portional to its electrica! conductivity.^) Now when the con- 

 duction resistance declinates while the positive ion increases in 

 strength, the most positive metals must be deposited primal and 

 mostiy; but is this the case, then the less positive metals must 

 in accordance with ordinary laws of chemistry be substituted 

 and received as the end-product of the process on the cathode. 



We shall prove, that this kind of deposition must be the 

 aim of everyone, who endeavoure to obtain satisfactory results 

 in electrodeposition of metals, and that in fact nearly all known 

 processes are based on this principle. 



Sorae metals, as for instance copper and silver, can be ob- 

 tained from a very acidulated Solution and it is a rule in copper 

 refineries to add sulphuric acid in order to decrease the conduc- 

 tion resistance. In this case the secondary processes are parti- 



') Magnus, Pogg. Ann. 102, s. 23, 1857. 



2) Arrhenius, Öfvers, tif K. Vet.-Akad. Förh. 1893, N:o 2, 115. 

 ') HiTTORF, Pogg. Ann. 103, s. 48, 1858, and Buff, Anu. Chem. u. Pharm. 

 105, 8. 156, 1858. 



