Flora — Estimation of Cadmium taken as the Chloride. 395 



the cadmium is deposited much more quickly from a solution 

 of its chloride than of the sulphate, aud the deposit in the 

 earlier part of the precipitation appears to be very satisfactory. 

 But the chlorine set free apparently has some action upon the 

 organic compound present to produce substances detrimental to 

 the process. With care, however, satisfactory results may be 

 obtained, as may be seen from a study of the following tables: 











Series A. 



— Urea. 











Cd. 



Urea. 



Cur't = 



N.Djoo. 



E.M.F. 



Time. 



Tot. 



vol. 



Cd. fd. 



Error. 





Nc 



). grm. 



grm. 



amp. 



amp. 



vts. 



min. 



cm 3 



grm. 



grm. 



Notes. 



1. 



0-1324 



3 



1-0 



3-0 



12 



20 



60 



0-1312 



— 0-0012 



( spongy, 

 X not all 

 ( out 



% 



0-1324 



2 



1-0 



3-0 



12 



30 



60 



0-1336 



4-0-0012 



( spongy, 

 < not all 

 ( out 























3. 



0-1324 



3 



1-0 



3-0 



7-8 



15 



55 



0-1342 



+ 0-0018 



( very 

 ] spongy, 

 ( all out 



4. 



0-1324 



2 



025 



0-75 



7-8 



25 



60 



0-1324 



+ 0-0000 



all out 



5. 



0-1324 



2 



0-5 



1-5 



12 



20 



60 



0-1333 



+ 0-0009 



j sit. spy. 

 j all out 



6. 



0-1324 



1 



1-0 



3-0 



12 



20 



60 



0-1370 



+ 0-0046 



j very 

 ( spongy 



~ 



0-1324 



1-5 



0-25-0-5 



0-75-1 



5 7-8 



30 



60 



0-1328 



+ 00004 



good 



8. 



0-1324 



1-5 



0-25-0-5 



0-75-1 



5 7-8 



30 



60 



0-1329 



+ 00005 



fair 



The amount of urea present, therefore, should be between 

 1-5 grm. and 2 grms., and the current potential should not 

 exceed 8 volts, instead of the 12 volts permissible when cad- 

 mium sulphate was used. The test with hydrogen sulphide 

 does not seem to be very delicate in this solution, so that at 

 least 30 minutes should be allowed for each determination. 

 Some writers recommend the testing of the end-point in simi- 

 lar cases by raising the level of the liquid upon the cathode, 

 but this was not proved of much value in this work, as the 

 amount of metal deposited upon the fresh cathode surface from 

 the solutions near the end of the process is imperceptible. 



A solution to which formaldehyde was added gave the fol- 

 lowing results : 



Series B. — Formaldehyde (formalin). 



Tol. 





Cd. 



Form. 



Cur't = 



N.D I00 . E.M.F. 



Time. 



vol. 



Cd. fd. Error. 





No. 



grm. 



cm 3 . 



amp. 



amp. vts. 



min. 



cm 3 . 



grm. grm. 



Notes. 



1. 



0-1324 



3 



0-25-1-5 



0-75-4-5 7-8 



20 



45 



0-1333 +0-0009 



fair 



2. 



0-1324 



2-0 



0-50-2-0 



1-50-6-0 11-8 



15 



45 



0-1330 +0-0006 



sit. spgy 



3. 



0-1324 



1-5 



0-75 



2-25 7-8 



30 



60 



0-1324 ±0-0000 



compact 



4. 



0-1324 



1-5 



1-0 



3-0 7*8 



35 



60 



0-1325 +0-0001 



tt 



