54 Gooch and Kohayashi — Platinised Anode of Glass. 



Fig. 1. 



Fig. 2. 



These results point to the conclusion that the high current 

 density which is a necessary consequence of the use of the very 

 small anode with currents large enough to effect an electro- 

 lytic determination of manganese within a reasonable time is 

 impracticable. In the succeeding experiments, therefore, the 

 use was made of the rotating electrode of platinized glass, 

 described by Grooch and Burdick,"^ since this device affords a 

 large surface for the deposition with small expenditure of plati- 

 num. The anode used in these experiments was made by 

 heating, to a temperature sufficient to volatilize glycerine, a 

 tube of lead glass, shaped like a test tube, painting upon it a 

 viscous emulsion of dry chloroplatinic acid in glycerine, and 

 burning the film of deposited platinum into the glass at the 

 softening point of the latter. 



Connection of this platinum film with the rotating shaft was 

 made by platinum wire bound about the tube, reaching over 

 the edge of the latter, and pressed by a rubber stopper into- 

 contact with a strip of platinum foil in 

 electrical contact with the metal shaft. 

 An important modification of the original 

 form of this type of electrodef is the 

 attachment of the binding platinum wire 

 at a point so low that the wire will be 

 kept cool by immersion in the electrolyte 

 and thus avoid the possibility of cracking 

 the glass electrode by the over-heating of 

 the wire when carrying a high current. 

 This electrode is shown in the accom- 

 panying figure. 



With the anode of platinized glass two 

 sets of experiments were carried out. In 

 one set the cathode was a piece of plati- 

 num foil measuring 0*5 cm. x 5 cm. In 

 the other set of exj)eriments three ca- 

 thode foils of twice this size were em- 

 ployed, thus permitting the passage of 

 the same strength of current under a 

 lower potential. 



At the end of the electrolysis the solution was drawn off 

 by means of the filtering tube (fig. 2) made by fusing the 

 fiared end of a lead glass tube to a disc of platinum gauze 

 and coating the disc with a filtering mat of asbestos by 

 dipping it in an emulsion of asbestos and applying suction. 

 The hyd rated manganese dioxide deposited upon the anode 



*This Journal, xxxiv, 107, 1912. 

 f Loc. cit. 



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