178 



EEPORT — 1900. 



is done, accurate results can be obtained, our own determinations, which 

 need not be detailed here, confirming those of previous experimenters. The 

 continuous attention thus entailed of course robs the method of its 

 practical value. 



Experiments were made on the use of acid ammonium oxalate instead 

 of the neutral salt as the electrolyte, and it was found possible to complete 

 the electrolysis without the addition of oxalic acid, 6 gr. of the acid salt 

 being added to Q-l gr. of iron as ferric chloride. But there is always a 

 risk of ferrous oxalate separating out from this solution after the ferric 

 salt has been reduced, which is extremely difficult to redissolve, so that the 

 conditions of deposition were not regarded as worth further study. 



By working with a lower current density and allowing the electrolysis 

 to proceed for six hours, or preferably ovei-night, in cold solutions, it was 

 found that 5 gr. of ammonium oxalate will outlast the deposition of 

 0-2 gr. of iron, and these conditions afford a thoroughly satisfactoiy 

 method for the electrolytic determination of iron. The metal is deposited in 

 a steel -grey, coherent form, and adheres equally well to a polished or sand- 

 blasted dish ; the washing and drying can be done without any fear of 

 o.\.idation. 



After some preliminary experiments it was found that a C.D.mg of 

 0*4 to 0-5 ampere and anE.M.F. of 3-0 to 3'5 volts are best ; from five to 

 six hours are necessary for the deposition of 0-1 gr. of ii'on. The following 

 experiments illustrate the results to be obtained under these conditions ; 

 a ferric chloride solution was used, the excess of free acid being first 

 neutralised as in Series I. Nos. 8-1 2 were consecutive experiments. 



Series II. 



No. 



Iron 



taken, 



gr- 



1 

 2 



3 



4 

 5 

 R 



7 



8 







10 



u 



12 



01060 

 01060 

 01060 

 01060 

 OlOCO 

 01060 

 01060 

 00950 

 0-1840 

 0-1050 

 0-0920 

 0-0920 



Iron clu- 



posited, 



gr- 



0-1060 



0-1064 

 0-10,66 

 0-1065 

 1065 

 0-1065 

 0-1062 

 0-0920 

 0-1840 

 0-1050 

 0-0919 

 0-0919 



Ammonium 

 Oxalate Solu- 

 tion added, 



CO. 



125 

 125 

 125 

 125 

 125 

 125 

 125 

 125 

 125 

 125 

 125 

 125 



C.D.,(,„ 

 Anipere 



0-42 

 0-4 

 0-4 . 

 3 ■ 

 0-3 

 0-3 ■ 

 0-3 ■ 

 4 - 

 0-38- 

 0-4 ■ 

 0-6 . 

 0-5 - 



-0-6 



-o-(; 



-0-6 



-0-29 



-0-29 



-0-2 



-0-3 



-0-32 



-0-32 



-0-36 



-0-55 



-0-5 



Reparks 



Overnight 



Nutfi. — The two figures for Current and E.M.F. indif-.ate the measurements at the 

 beginning and end of the determinations respectively. 



Considerable latitude is permissible in the cun-ent density and E.M.F., 

 but it should be on the low side of the values given above. The deter- 

 minations require no watching, and by allowing them to proceed overnight 

 one of the most marked advantages of electrolytic analysis is gained. 



Experiments made under similar conditions in warm solutions indi- 

 cated no advantages whatever ; the rate of deposition is not increased, 

 and there is always .ti greater risk of ferric hydrate separating out, as 

 already explained 



