Flora — Cadmium by Means of the Rotating Cathode. 455 



rent will be retarded, and even prevented altogether if the 

 nitric acid be present in sufficient amount. Upon this behavior 

 have been based methods for the separation of copper, bismuth 

 and mercury from cadmium.* Tests were made by me to 

 determine the amount of free nitric acid necessary to prevent 

 deposition of the cadmium, and it was found that 2 cn ' 3 of nitric 

 acid of 1 : 4 dilution in 50 cm3 of solution (approximately 1 per 

 cent of free acid) will absolutely prevent the precipitation of 

 the cadmium upon the cathode (current, 3 amperes ; E.M.F., 7*5 

 volts). If less nitric acid was used, traces of cadmium were 

 deposited upon the cathode. 



Summary of Results obtained in the Estimation of Cadmium by 

 means of the Rotating Cathode. 



The results of the work described in this and the previous 

 papers upon the estimation of cadmium by means of the rota- 

 ting cathode may be briefly summarized as follows: Under the 

 conditions used, cadmium taken in the form of the sulphate 

 may be very accurately and satisfactorily estimated by deposi- 

 tion from solutions containing sulphuric acid, sodium acetate 

 and acetic acid, or potassium cyanide ; but little less satis- 

 factorily from solutions containing urea, formaldehyde or 

 acetalclehyde ; and also with proper precautions, from solutions 

 containing pyrophosphates, phosphates, tartaric acid or formic 

 acid. From solutions containing oxalates or oxalic acid, 

 ammonium tartrate, or potassium formate, however, I was 

 unable to obtain satisfactory deposits. When taken as the 

 chloride, cadmium does not permit such a wide range of condi- 

 tions. Nevertheless, from solutions of the chloride containing 

 sulphuric acid or potassium cyanide, or the pyrophosphates, 

 the metal is deposited in a form comparable with that obtained 

 when cadmium sulphate is taken. Solutions of the chloride 

 of cadmium to which is added hydrogen disodic phosphate 

 gave less desirable results ; while solutions containing urea, 

 formaldehyde or acetaldehyde gave deposits free from spongi- 

 ness only after careful regulation of the conditions. In addition 

 to the solutions containing the oxalates, oxalic acid, the for- 

 mates and the tartrates, negative results were given in the case 

 of the chloride by solutions containing the acetates, formic 

 acid, and tartaric acid. The nitrate of cadmium is ill-fitted for 

 electrolytic estimation, the cyanide solution being the only one 

 from which satisfactory results were obtained. From solutions 

 containing one per cent or more of free nitric acid, the cadmium 

 is not deposited by the current. 



* Edgar F. Smith, Am. Ch. J. ii, 42 (1880) ; Smith and Mayer, J. Ch. Soc, 

 lxiv, ii, 496 (1893); Kammerer, J., Am. Ch. Soc, xxv, 94 (1903); Eudorff, 

 Z. angw. Ch. (1894), 388. 



