Flora — Estimation of Cadmium taken as the Sulphate, 271 











Series B. 













Cd. 















Cd. 







• taken. 



NaOH. 



K 2 S0 4 . 



Cur't - 



N.D 100 



E.M.F. 



Time. 



found. 



Error. 



No. 



grm. 



grm. 



grm. 



amp. 



amp. 



vts. 



min. 



grm. 



grm. 



1. 



0-1491 



excess 



0-5 



1-25 



3'7o 



8-0 



10 



0-1496 



+ 0-0005 



2. 



0-1491 



0-2 



0-5 



0-8. 



2-4 



8-0 



15 



0-1491 



+ 0-0000 



3. 



0-1491 



0-2 



0-5 



0-8 



2-4 



8-0 



15 



0-1493 



+ 0-0002 



4. 



0-1 223 



0-5 



0-2 



1-0 



3-0 



12*0 



20 



0-1223 



±0-0000 



5. 



0-1223 



0-5 



0-2 



1-0 



3-0 



12-0 



20 



0-1223 



±0-0000 



6. 



0-1223 



0-2 



0-5 



1-25 



3-75 



1-5 



10 



0-1227 



+.0-0004 



In both series the volume of the solution was about 60 ctn3 to 

 65 cm3 . The sixth experiment in each series will indicate the 

 result when the greater concentration of 45 cm3 to 50 cm3 was tried. 

 In these cases the precipitate showed a tendency to sponginess, 

 which was more noticeable in series A. At the greater dilu- 

 tion, the deposition of the cadmium proceeds rapidly and satis- 

 factorily ; the deposit is rather crystalline, fairly compact, and 

 easily washed, so that the method forms one of the very best 

 where the cadmium is taken in the form of the sulphate : the 

 chloride and nitrate behave differently and will be treated 

 later. The second modification seemed to give deposits more- 

 satisfactory than the first. Certain cautions, however, are to 

 be observed. Not more than 0*1500 grm. may safely be esti- 

 mated ; the normal current density should not exceed 3*0 

 amperes if a spongy deposit is to be avoided ; and, for the 

 same reason, a large excess of electrolytes is to be avoided. 



III. In Solutions containing Cyanides. 



The deposition of cadmium from a solution of the double 

 cyanide has always been very satisfactory, and the results with 

 the rotating cathode were in complete accordance with previous 

 work on this method. The range of conditions of current and 

 quantity of electrolyte is broad, the deposit is a beautiful 

 silvery plate, so compact as to be rubbed off onty with diffi- 

 culty, which dries very quickly ; and although the complete 

 deposition of the metal is not so rapid as it is from solutions 

 containing sulphates or acetates, it is sufficiently rapid. Care 

 should be taken to avoid foaming of the solution, as this 

 retards somewhat the deposition of the final traces of cadmium. 

 Generally, a volume of 65 cm8 to T0 cm3 was found most satisfac- 

 tory. The solution was run off into a beaker of convenient 

 size, the cadmium precipitated with sodium hydroxide, and the 

 precipitate redissolved in potassium cyanide. The following 

 results were obtained : 



