108 Qoooh and Burdick — Electro- Analysis with 



cathodes were made in this manner, and tested. A straight tube 

 with open end, an ordinary test-tube, the bulbed tube, and 

 the cup made from a thistle tube are all serviceable : but the last, 

 shown in figure 1, is most convenient in use. This electrode is 

 easily made by platinizing the thistle T of a lead glass thistle- 

 tube about 3-5 cm in diameter, and then drawing out and sealing 

 off the straight tube at its junction with the thistle. The 

 electrode is fitted to a perforated rubber stopper s, which is 

 slipped tightly over the vertical shaft of the motor. The 

 shaft carries the current, and the electrical connection is made 

 between the shaft and the platinum film 

 " p by means of foil f attached to the for- 



mer and wire w twisted about the latter, 

 the wire and foil being pressed into con- 

 tact between the glass and the stopper. 

 Before using, the electrode is rinsed thor- 

 oughly in hot nitric acid, washed with 

 water, dried in an air bath, and weighed. 

 Following are the results of tests in 

 which these electrodes were used as the 

 cathode rotating at the rate of about 300 

 revolutions to the minute. The anode 

 was platinum foil placed vertically, and 

 the electrolyte, 50 cm3 in volume, was con- 

 tained in a beaker. The solution of 

 electrolyte was in each case standardized by electrolysis with 

 the rotating platinum crucible used as cathode. 



Electrolysis of Copper Sulphate* 



Initial 

 Copper Copper current 



taken found Error , ' , Approx. Time 



grm. grm. grm. amp. volt. N.D. 100 min. 



Platinized test-tube used as cathode. 



0-1279 0-1277 —0-0002 2 .. 10 30 



0-1280 0-1278 —0-0002 T8 .. 9 30 



0-1272 0-1272 0-0000 2 .. 10 30 



Platinized tube, open at end, used as cathode. 



'01272 0-1265 —00007 2-1 5'5 10-5 40 



0-1272 0-1265 -0-0007 2 5"5 10 40 



01272 0-1772 —0-0000 1 6 5 30 



Platinized thistle-tube used as cathode. 



0-1272 0-1272 —00000 2 5-5 10 30 



0-1272 0-1265 —0-0007 .. .. .. 30 



0-1272 0-1266 —0-0006 .. .. .. 30 



0-1272 0-1268 0-0004 .. ._ .. 30 



* Acidulated with EUS0 4 . 



