]7G REPORT — 1900, 



added and the current increased to 1-0 ampere at the end of the determina- 

 tion to ensure the precipitation of the last portion of the iron. According 

 to Wolman, eight to ten hours ai-e necessary for the deposition of 0' 15 to 

 0-30 gr. of iron with a C.D.,no=0"3 to 1-0, and finally to 1'5 ampere, and 

 an E.M.F. of 4 volts at 50° C. The majority of the results recorded by 

 this method are slightly low, on an average 0-2 to 0-6 per cent, on the 

 weight of iron taken. 



Variations in current and in the proportion of ammonium oxalate 

 added constitute the only real differences in the conditions of deposition 

 recommended, and they bear on the one practical difficulty of the method — 

 the prevention of the separation of any ferric hydrate during the electro- 

 lysis. As pointed out in a previous report (1896) on the electrolytic de- 

 termination of tin in ammonium oxalate solution, the electrolyte gradually 

 becomes alkaline, owing to the decomposition of the oxalate and the for- 

 mation of ammonium carbonate ; in jiresence of a sufficient excess of 

 ammonium oxalate the iron will still remain in solution after the latter is 

 alkaline, but otherwise ferric hydrate separates out and oxalic acid must 

 be added from time to time during the electrolysis to redissolve it. Such 

 addition of oxalic acid renders it necessary to watch the experiment ; a 

 further drawback is that the quantity of ammonium oxalate solution 

 necessai-y leaves little room for any further addition of liquid in an ordi- 

 nary dish of 175 c.c. to 200 c.c. capacity. Hence the ammonium oxalate 

 must outlast the deposition of the iron if an addition of oxalic acid is to be 

 avoided. A series of experiments were, therefore, first arranged in which 

 the time necessary for the solution to become alkaline, the propoi'tion of 

 metal deposited up to alkaline reaction, and the proportion subsequently 

 deposited, were noted. 



A ferric chloride solution of known strength was used, made up from 

 pure ferric oxide, the method of working being as follows : — The slight 

 excess of hydrochloric acid in the measured portion of the solution was 

 first neutralised with a few drops of ammonium hydrate, oxalic acid 

 solution added to acid reaction, and the whole then added to the ammonium 

 oxalate solution. The additional oxalic acid recorded was either added to 

 the original solution or at intervals during the electrolysis. The current 

 density, C.D.ino=l"0 to 1-5 ampere, and electromotive force of 3-5 to 4-0 

 volts employed in these first experiments are the values hitherto regarded 

 as the most favourable for the deposition of iron. Both warm and cold 

 solutions were tried. The ammonium oxalate solution contained 40 gr. 

 per 1.000 c.c. ; the oxalic acid solution 80 gr. per 1,000 c.c. 



Platinum dishes of about 200 c.c. capacity were used as the cathode 

 and bored platinum discs as the anode ; the circuits and measurements 

 were arranged as described in the Committee's third report (1896). 



The following results illustrate the conclusions to be drawn from this 

 series of experiments : — 



Series I. 



In experiments 1, 2, 3, 4, and 5, 10 c.c. of oxalic acid solution were added 

 to the solution prepared as stated above and the electrolysis continued 

 until the mixture became alkaline, when the current was broken and the 

 deposited metal washed, dried, and weighed in the usual manner. The 

 solution became alkaline very quickly when electrolysed warm, but on an 

 average about 25 per cent, of the total iron was deposited in this short 

 pei'iod of fifteen to twenty minutes. Although alkaline, no separation of 



