ON THE ELECTROLYTIC METHODS OF QUANTITATIVE ANALYSIS. 177 



ferric hydrate took place up to this stage, there being sufficient ammonium 

 oxalate left to keep the iron salt in solution. In experiments 6 and 7 

 a larger proportion of oxalic acid solution (50 c.c.) was added to the 

 original solution, which allowed the electrolysis to be continued for 

 H hour before alkalinity was reached ; the rate of deposition is evidently 

 slowed by this increase of free acid. When cold solutions are electrolysed 

 the deposition is quicker, as shown in experiments 8 and 9 ; the larger pro- 

 portion of metal deposited is also partly due to the somewhat higher 

 current and E.M.F. employed, and, taking this into account, the solution 

 takes longer to get alkaline when electrolysed cold, as would be expected, 

 since the rate of the decomposition of the oxalate will be slower. A 

 comparison of experiments 5 and 8 with the remainder shows that, 

 with less iron and the same proportion of oxalate, there is an increase 

 in the proportion of iron deposited, despite the retarding effect of the 



relative increase of free oxalic acid present. In experiments 10 and 11 

 the solutions were electrolysed till alkaline, and the deposited metal 

 weighed (a) ; the solution was then poured back into the dish, and the 

 electrolysis continued until a precipitate of ferric hydrate separated, when 

 the additional iron deposited on the cathode Avas weighed (b). The 

 deposition in both warm and cold solutions proceeds more rapidly after 

 alkalinity than before, and there is evidently little difference in the 

 results of the two experiments. 



It is clear from these results that 5 gr. of ammonium oxalate will 

 not outlast the deposition of 0-1 gr. of iron under the above condi- 

 tions of current and E.M.F. ; further, that an initial acidiiication with 

 oxahc acid up to 4 gr. is no real help in preventing a separation of 

 hydrate ; and, finally, that it is advantageous to electi'olyse cold solutions 

 in preference to warm. To complete the deposition of iron under these 

 circumstances it is necessary to add oxalic acid from time to time durina 

 the experiment, so as to prevent the separation of ferric hydrate ; if this 



1900. jj 



