Platinum Electrodes of Light Weight. 



Ill 



Fig. 3. 



f^ 



At the end of the electrolysis the cathode is disconnected 

 from the shaft and washed in the cell. Loose particles of the 

 deposit are allowed to settle, and the supernatant liquid is 

 decanted. After washing by decantation with 

 water, and finally with alcohol, the cell and 

 cathode are dried in the air bath, and weighed. 

 Data and results of the procedure applied to 

 copper sulphate, standardized by means of the 

 rotating crucible, are given on the preceding 

 page. 



The results are reasonably good, but the 

 difficulty of washing thoroughly by decantation 

 without loss of any loose particles, and with 

 complete removal of the washing liquid so that 

 the drying process need not be prolonged unduly, 

 is considerable. To meet this difficulty we make 

 use of the little filter tube shown in figure 3. 

 This is made by fusing the end of a lead glass 

 tube, flared slightly, to a little disc of platinum 

 foil perforated by a sharp point, the rough edges 

 of the perforations being turned outward. By 

 applying the suction of the filter pump to the open end of the 

 tube, and dipping the disc end into an emulsion of asbestos, 

 a felt of asbestos is deposited upon the 

 perforated disc. The tube and felt may 

 be dried, and even ignited, without diffi- 

 culty. 



This little reverse filter is dried and 

 weighed with the cell and cathode ready 

 for use. The electrolysis is made in the 

 manner previously described. The liquid 

 of the cell and the washings of the cathode 

 and cell are drawn off through the reverse 

 filter. The stand, cell, cathode, and reverse 

 filter, shown in figure 4, are dried and 

 weighed together. Results of this proce- 

 dure, applied to the determination of cop- 

 per in copper sulphate and of nickel in 

 nickel ammonium sulphate, are given in 

 the table below. 



For comparison, a few determinations were carried out, 

 otherwise similarly, without rotation of the cathode. In 

 this case the deposit was much more bulky, rather difficult 

 to dry thoroughly, and perhaps more sensitive to oxidation. 

 Results obtained in this manner are also given in tabular 

 form. 



Fig. 4. 



