July 16, 1915] 



SCIENCE 



95 



(D) Eleetrolyze retort residue C — copper, anti- 

 mony and bismuth will be deposited witli a cathode 

 potential limited to 0.45 volts (against the nor- 

 mal calomel electrode). 



(E) Dissolve metal deposit D in nitric acid plus 

 tartaric acid, and precipitate bismuth as bismuth 



(F) Eleetrolyze filtrate E with a limited cath- 

 ode potential — copper alone will be deposited. 

 Antimony is obtained iy difference. 



((?) Eleetrolyze residue D with a cathode po- 

 tential limited to 0.7 volt against the normal cal- 

 omel electrode: tin and lead will be deposited. 

 Treat the deposit with nitric acid plus potassium 

 nitrate: the solution contains all the lead, and this 

 metal may be deposited as lead peroxide, or the 

 residue of tin oxide may be dissolved in hydro- 

 chloric acid plus hydroxylamine and the tin deter- 

 mined by electrolysis. 



(H) Eleetrolyze residue G to obtain cadmium 

 or other metals. 



P. ScHOCH and W. A. Pelsing: The Influence of 

 the Potassium Ion upon the Potential of the 

 Ferrocyanide-ferricyanide Electrode. 



The potential of the ferrocyanide-ferricyanide 

 electrode is made more noble by the addition of 

 potassium salts to the electrolyte, but the amount 

 of this change in potential is much greater than 

 the amount calculated from the change in the 

 ratio of ferrocyanide to ferricyanide ions when 

 the concentrations of the latter are calculated from 

 the conductivity ratio and with the aid of the rule 

 of mixtures as set forth by Sherrill. It was sug- 

 gested by Lewis that this extra effect may be due 

 to th© potassium ion taking part in the pole reac- 

 tion. Thus, with the uudissociated salts, the re- 

 action would be: K3re(C!N)3 plus K-ion plus one 

 electron gives K,Pe(CN)5 — and it has been shown 

 recently by Mueller that with concentrations of 

 potassium ion ranging from 0.2 normal to 0.8 nor- 

 mal the amount of change in potential corresponds 

 to the amount of change in the potassium ion if 

 the concentration relations of the other substances 

 remains constant. Since the latter is not likely to 

 be true, and since the potassium ion shows the 

 same influence even in the most dilute solutions 

 tried, the authors sought to ascertain whether or 

 no the concentration influence of the potassium 

 ion is constant with a particular power of its con- 

 centration. This was found to be the ease with 

 the .75 power of the potassium ion concentration, 

 and if the ferrocyanide and the ferricyanide ion 



concentrations are calculated from the conductivity 

 ratio and the rule of mixtures. The various mix- 

 tures tried present a range of total potassium ion 

 concentration from 7.8 millimol to 395 millimol 

 per liter. In some mixtures the potassium ion was 

 derived wholly from the iron cyanides, in others, 

 almost wholly from potassium chloride, and in 

 others still, partly from both sources. The differ- 

 ent potentials thus reduced to unit concentrations 

 present a maximum range of 8 millivolts with this 

 large variation of concentrations, and hence the 

 result may be considered to be constant. Further- 

 more, it is likely that on repetition measurements 

 will be obtained which will show considerably less 

 variation. 



Since the calculations of the above potentials in- 

 volve the general dilution law of strong electro- 

 lytes and the rule of mixtures, it was desirable to 

 test these calculations in some way, hence the con- 

 ductivities of these mixtures were measured and 

 compared with their calculated values. When al- 

 lowance is made for the influence of the viscosities 

 of the solutions, then the observed and the calcu- 

 lated conductivities agree to one per cent, and less. 



The work is now being repeated with calcium 

 salts in place of potassium salts. Although the 

 immediate result of this work is the establishing of 

 an empiric relation between concentrations and 

 pole potentials, yet it is likely that the results will 

 throw some light on the manner of ionization of 

 salts with polyvalent ions — particularly because 

 other electrodes such as the thallous-thallic, the 

 ferrous-ferric and the mercurous-mercuric, show 

 similar relations. 



E. Gr. Van Name and D. U. Hill: The Bates of 

 Solution- of Metals in Ferric Salts and in 

 Chromic Acid. 



The observed rates of solution were lowered by 

 increasing the concentration of free sulphuric acid. 

 In ferric sulphate with 0.5-molar acid the rates 

 differed and were higher the more electropositive 

 the metal. With 10-molar acid the four most elec- 

 tropositive metals tested all gave the same rate. 

 The lowering of the rate with increasing acidity is 

 due to increase in the viscosity, which retards the 

 diffusion. In general all results are in agreement 

 with the diffusion theory of heterogeneous reac- 

 tions, but the marked dependence upon the nature 

 of the metal, observed at the lower acidity, contra- 

 dicts Nernst's hypothesis that, where no secondary 

 effects interfere, the rate of the chemical reaction 

 proper (as distinguished from the diffusion proc- 

 ess) must always be extremely high. 



