Flora — Estimation of Cadmium taken as the Sulphate. 269 



results were therefore taken as indicating the standard of the 

 solution used, the mean of the series showing the presence of 

 0*0074:54 grin, of cadmium in each cubic centimeter of the 

 solution. 



In a second solution which it became necessary to standard- 

 ize the following results were obtained : 









Solution B. 







No. 



Sol. 





Cur't 







Cd. 



of 



taken. 



Time. 



read. = 



N.D 100 



E.M.F, 



found. 



Exp. 



cm. 



min. 



amp. 



amp. 



vts. 



grm. 



1. 



20 



27 



10-1-5 



3-0- 4-5 



7-9 



0-0816 



2. 



25 



30 



2-0-3-0 



6-0-9-0 



7-9 



0-1018 



3. 



25 



55 



2-5-4-0 



7-5-12-0 



7-6 



0-1019 



4. 



30 



25 



20-2-5 



6-0- 7-5 



12-0 



0*1224 



5. 



30 



20 



1-0 



3-0 



7-8 



0-1223 



6. 



30 



10 



1-5-2-5 



4-5- 7-5 



7-8 



0-1226 



The mean of these six experiments gives a value of 0*10194: 

 grm. of cadmium for every 25 em3 of the solution, or 0*0040776 

 grm. for each cubic centimeter. This value was taken as the 

 standard whenever this solution was used. 



One point which was not mentioned in the former paper* on 

 the estimation of cadmium by this method, but which is of 

 much importance, is that of dilution. The earlier experiments 

 in this work were performed at a dilution of from 65 cm3 to 75 cm3 . 

 Much trouble was experienced, however, at this dilution ; for 

 the last traces of the metal were driven from the solution only 

 with extreme difficulty and with much loss of time, as may be 

 noted by comparing the time interval of most of the experi- 

 ments with the shorter interval of the last two experiments of 

 the second series, where the dilution was 45 to 50 cm . More- 

 over it was found advisable, in order to avoid mechanical 

 loss, to deposit not more than 0*2 grm. to 0*25 grm. of the 

 metal upon the cathode, while even smaller quantities are to 

 be preferred. The current density must also be kept within 

 the limits indicated; for otherwise a spongy deposit may result. 

 Cadmium seems to be especially liable to the formation of 

 these spongy, unweighable deposits, and the greatest difficulties 

 experienced in this investigation have come from this behavior 

 of the metal. 



The best condition, therefore, may be briefly summarized as 



follows: Cadmium sulphate, equivalent to not more than 



0-2 cm to 0-25 grm. of the metal, is dissolved in 45 cm3 to 50 c,n3 of 



water ; ten to fifteen drops of dilute sulphuric acid are added ; 



and the proper connections made and the solution subjected to 



electrolysis as described, fifteen minutes being sufficient time 



for the complete deposition of the metal upon the cathode. It 



* Loc. cit. 



Am. Jour. Sci. — Fourth Series, Vol. XX, No. 118.— October, 1905. 

 19 



