270 Flora — Estimation of Cadmium taken as the /Sulphate. 



is not necessary to heat the liquid, as the passage of snch large 

 currents soon heats it sufficiently. When electrolysis is com- 

 plete, the excess of sulphuric acid may be destroyed with a 

 slight excess of ammonia water, the current broken, and the 

 cathode removed, thoroughly rinsed with water and alcohol, 

 and dried by waving over a free flame. If the deposit is not 

 spongy the drying is a matter of only a few moments, and 

 there is no danger of oxidizing the metallic deposit. If it is 

 preferred, the current may be reduced by interposed resistance, 

 the rotation stopped, and the liquid readily siphoned without 

 danger of injuring the metallic coating. 



II. In Solutions containing Acetates. 

 The next method to be studied in its application to the rotat- 

 ing cathode was the use of solutions containing acetates, as 

 recommended by Edgar F. Smith. Originally, Smith used a 

 solution obtained by dissolving cadmium oxide in acetic acid* 

 but later found that the electrolysis proceeded equally well in 

 solutions containing the nitrate, chloride or sulphate of cad- 

 mium with an excess of sodium acetate.f In the study of the 

 application of this method to the estimation of cadmium, taken 

 as the sulphate, upon the rotating cathode, two methods of 

 proceeding were followed, both of which had been previously 

 used by ExnerJ in his work upon the rotating anode. In 

 series A, of the experiments following, measured amounts of 

 cadmium sulphate solution were run off from a burette, the 

 indicated amount of sodium acetate was added in solution, a 

 small amount of potassium sulphate was added to increase the 

 conductivity of the solution, the whole diluted to the desired 

 volume and electrolysis conducted as with the solution contain- 

 ing sulphuric acid. In series B, the cadmium in the measured 

 solution was precipitated as the hydroxide with a sodium 

 hydrate solution, the precipitate dissolved in a very slight 

 excess of acetic acid, potassium sulphate added as before, and 

 the solution subjected to electrolysis. 





Series A. 









Cd. 

 taken. NaOC 2 H 3 0. K 2 S0 4 . 



Cur't 

 read. ~ 



N.D 100 . 



E.M.F. Time. 



Cd. fd. 



Error. 



No. grm. grm. grm. 



amp. 



amp 



vts. min. 



grm. 



grm. 



1. 0-1864 1*5 0-5 



2-0 



6-0 



8-0 



(§) 







2. 0-1491 2-0 1-0 



1-5 



4-5 



8-0 15 



(II) 







3. 0-1118 0-5 1-0 



1-0 



3-0 



8-0 20 



0-1121 



+ 0-0003 



4. 0-1491 1-5 0-5 



0-9 



2-7 



8-0 15 



0-1494 



+ 0-0003 



5. 0-1491 1-5 0-5 



0-9 



2-7 



8-0 15 



0-1496 



4-0-0005 



0. 0-1223 1-5 0-5 



0-75 



2-25 



7'5 20 



0-1237 



+ 0-0014 



* Ber., xi, 2048 (1878). f Am. Ch. J., ii, 41 (1880). 

 X J. Am. Ch. Soc, xxv, 896 (1903). 



£ Did not weigh, as precipitate was non-adherent. Current too high for quantity of 

 cadmium present. | Deposits spongy and blistered. Too much electrolyte present. 



