with the Mercury Cathode. 



the position of the platinum cathode was changed twice during 

 the plating. First the prong of a right angle hent piece was 

 inserted between the rotating gauze discs nearly to the central 

 stem of the anode and about one-third the silver, say two grams, 

 deposited; then the cathode was pointed at a 45° angle between 

 the stem and the upper disc and a little more silver deposited. 

 The point where the stem passes through this disc seems to be 

 the most difficult place to cover. Finally the cathode was 

 removed to a position below the anode and the electrolysis 

 continued until the electrolyte was silver free. The weight 

 of the anode was generally increased about 5 grms. as a result 

 of the plating. Only once was unplated platinum, presumably 

 the same as noticed by Goldbaum,* seen by the writer, and 

 then as black specks appearing on the center stem between the 

 disc, and these were easily covered by plating on a few tenths 

 of a gram more silver with the cathode between the discs. 



Electrolysis. — For an electrolysis about 2 kg. of mercury 

 was placed in the apparatus, the amount of sodium chloride — 

 generally 50 cm3 of the *1N solution — was introduced into the 

 inner cell and about 70-90 cm3 of water into the outer cell with 

 l cm8 of saturated salt solution. The plated anode was intro- 

 duced, rotated at a speed of 200-300 r.p.m. and the current 

 applied. After the first few experiments no particular attention 

 was paid to the speed of the rotation of the anode. "When 

 the electrolysis was considered sufficient and the current 

 discontinued the anode was withdrawn, washed, and dried by 

 appropriate means. The contents of the inner cell were 

 pipetted out — when separate titration was necessary — the 

 remainder of the solution washed into a separatory funnel and 

 separated from the mercury by three washings. The contents 

 of the outer cell were titrated by hydrochloric acid, using 

 methyl orange, generally at a dilution of 250 on ' 3 . When other 

 dilution was used correction for that volume was made at the 

 time. The inner cell was titrated by approximately 'VS. 

 sulphuric acid. The end-point in all titrations was obtained 

 by using a sodium hydroxide solution, about "06N", to dis- 

 charge the pink color of the indicator. 



In some cases, as in obtaining the results given in Table VI, 

 where it was unnecessary to separate the contents of the inner 

 and the outer cells, hydrochloric acid was added directly to the 

 liquid above the mercury to about the neutral point to methyl 

 orange, then the whole was shaken in a separatory funnel to 

 decompose the last of the amalgam and the titration finished 

 in an Erlenmeyer beaker in the absence of more than a few 

 tenths of a gram of the mercury at a volume of 250 cmS . This 

 procedure was shorter and to be preferred to the complete sepa- 



*Jour. Amer. Chern. Soc, xxxiii, 42. 



