45.1 Flora — Cadmium by Means of the Rotating Cathode. 



Art. XL VII. — Additional Notes upon the Estimation of Cad- 

 mium by Means of the Rotating Cathode, and Summary / 

 by Charles P. Flora. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cxli.] 



I. The Behavior of Cadmium Nitrate. 

 Since cadmium is not readily precipitated by the electric 

 current from solutions containing even small amounts of free 

 nitrate acid, it was to be expected that cadmium nitrate 

 would prove to be little fitted for estimation by electrolysis, 

 since the action of the current would produce nitric acid. 

 This, in general, was the result of my experiments upon the esti- 

 mation of cadmium in the form of the nitrate upon the rotat- 

 ing cathode. The deposits obtained from solutions containing 

 sulphuric acid, the phosphates, pyrophosphates, urea or formal- 

 dehyde, were satisfactory, but the time necessary for complete 

 deposition is so prolonged that these solutions are compara- 

 tively valueless for the estimation of cadmium taken as the 

 nitrate, since it would be easier and more trustworthy to trans- 

 form the salt to the sulphate by evaporation with sulphuric 

 acid before electrolyzing. With solutions containing acetic 

 acid the metal was not precipitated, except in a narrow ring at 

 the surface of the liquid. The behavior of solutions contain- 

 ing formic acid, tartaric acid, acetaldehyde and formaldehyde 

 was similar, but less pronounced. The only solution from which 

 1 was able to obtain satisfactory results in the estimation of 

 cadmium nitrate was a solution containing potassium cyanide. 

 This solution was prepared by adding to the solution of cad- 

 mium nitrate, which had been standardized by the precipitation 

 and ignition of the carbonate, the desired amount of sodium 

 hydroxide, and then redissolving the precipitated hydroxide in 

 an excess of potassium cyanide. The time needed for com- 

 plete deposition is somewhat longer than that required where 

 the chloride and sulphate of cadmium were taken, but the 

 deposit was bright and very satisfactory. Care must be used 

 to avoid the use of too large an amount of potassium cyanide. 

 The following table shows the results obtained : 

















Tot. 







No. Cd. 



KCN. 



NaOH. 



Cur't = 



N.D100. 



E.M.F. 



Time. 



vol. 



Cd. f d. 



Error-. 



grm. 



grm. 



grm. 



amp. 



amp. 



vts. 



min. 



cm 3 . 



grm. 



grm. 



1. 0-0920 



1-5 



0*5 



4-0 



12'0 



7-8 



45 



60 



0-0933 



+ 0-0013 



2. 00920 



1-0 



5 



3-0 



9-0 



7-6 



35 



60 



0-0924 



+ 0-0004 



3. 0-1073 



0-7 



0*5 



2-5 



7-5 



7'7 



50 



60 



0-1072 



—o-oooi 



II. The Behavior of Solutions containing Free Nitric Acid. 

 If free nitric acid be added to a solution containing a salt of 

 cadmium, the precipitation, of the cadmium by the electric cur- 



