392 Flora — Estimation of Cadmium taken as the Chloride. 



Art. XL. — The Use of the Rotating Cathode for the Esti- 

 mation of Cadmium taken as the Chloride ; by Charles P. 

 Flora. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cxl.J 



In a previous paper* the author has described the use of the 

 rotating cathode for the estimation of cadmium taken as the 

 sulphate. In the present paper a simular study has been made 

 of the behavior of cadmium when taken in the form of the 

 chloride. Some differences are to be expected, since it has 

 been established with some certainty that cadmium chloride, 

 when subjected to electrolysis, forms not only positive cadmium 

 ions and negative chlorine ions, but also complex cadmium- 

 chlorine negative ions ; and, in addition, the chlorine, when set 

 free, does not recombine with the water, to set free oxygen, 

 but exists in the solution in its free state. That there are some 

 very important differences a few qualitative experiments 

 showed, so that the study of the estimation of cadmium when 

 taken in the form of this salt was now undertaken. 



A solution was made up to a convenient strength, and the 

 standard determined by the mean of several closely agreeing 

 determinations by the carbonate method, which the author 

 had carefully tested and found to be perfectly reliable. This 

 showed 0'1589 grm. of cadmium in 30 cm3 of the solution, or 

 0-0052966 grm. per cubic centimeter. 



I. In Solutions containing Sulphuric Acid. 



The procedure with cadmium chloride was the same as with 

 the cadmium sulphate, and the results were very satisfactory. 

 But emphasis is to be laid upon the dilution in this case espe- 

 cially, for it was found that from the more dilute solution it is 

 almost impossible to drive the last traces of cadmium. A dilu- 

 tion of 45 cm3 was found to give the most satisfactory results. 

 To this solution ten drops of sulphuric acid of 1:4 dilution 

 were added before electrolysis. The following results were 

 obtained under these conditions : 





Cd. 



Curt = 



N. D 100 



E.M.F. 



Time. 



Cd. fd. 



Error. 



No. 



grm. 



amp. 



amp. 



vts. 



min. 



grm. 



grm. 



1. 



0-1059 



1-0-1-5 



3-0-4-5 



6-5-7-8 



25 



0-1054 



—0-0005 



1. 



0-1059 



2-0-3-0 



6-0-9-0 



7-8 



15 



0-1058 



—o-oooi 



IT. In Solutions containing Acetates. 



The acetate method has proved one of the most satisfactory 

 for the estimation of cadmium sulphate, but strangely enough, 

 * This Journal, xx, 268 (1905). 



