ON THE ELECTROLYTIC METHODS OF QUANTITATIVE ANALYSIS. ] 



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The electrolytic metliods for the determination of iron can in no way 

 be regarded as comparable with the usual volumetric and gravimetric 

 methods in their general applicability. Under special circumstances, how- 

 ever, they may be found advantageous, especially in the determination of 

 relatively small quantities of iron in organic products, an application 

 which has been specially studied in the subjoined experiments. 



Of the various methods proposed, that in which the metal is deposited 

 from a solution of the double ammonium oxalate, first suggested by 

 Parodi and Mascazzini, and subsequently worked out by Classen, is the 

 most reliable. When separated from a citrate or tartrate solution, the 

 precipitated iron contains a considerable proportion of carbon, and the 

 deposition from phosphoric acid or ammonium pyrophosphate solution is 

 too slow to be of practical value ; further, it necessitates a high current 

 density, and the introduction of phosphates into the solution is an obvious 

 disadvantage from an analytical standpoint. 



The experiments have therefore been restricted to the investigation of 

 the deposition of iron from the solution of the double ammonium oxalate. 

 They may be conveniently grouped under the following heads]: 



1. The condifAons under ivJnch iron is deposited from ammonium oxa- 

 late solutioii and the inost favourahle conditions for its electrolytic deter- 

 mination. 



2. The influence of ammonium chloride on the electrolytic determina- 

 tion of iron. 



3. The comjilete separation of the iron when deposited from ammonium, 

 oxalate solution : the sulphocyanide reaction for iron under the conditions 

 of the experiments. 



4. The presence of carbon in iron deposited from ammonium oxalate 

 solution and the determination of its amount. 



5. The electrolytic separation of iron and manganese in ammonium oxa- 

 late solution. 



6. The electrolytic determination of iron in urine and other animal pro- 

 ducts. 



1. The Conditions under tohich Ironis deposited from Ammonium G.valate Solution 

 and the nioxt famurahle Conditions for its Electrolytic determination. By 

 Chaeles a. Kohn, M.&C., Ph.D., and H. H. Froysell. 



Classen recommends the addition of 6 to 8 gr. of ammonium oxalate 

 per gr. of iron in 150-175 c.c. of solution, and conducts the electrolysis 

 with a CD., 00 of 1-0 to 1-5 ampere and 3 to 4 volts in a warm solution 

 (40''-60° C). Nitrates, if present, must be removed by repeated evapora- 

 tion with sulphuric or hydrochloric acid ; free sulphuric acid can be 

 neutralised by ammonium hydrate ; any free hydrochloric acid is prefer- 

 ably removed by evaporation on the water-bath. The complete deposition 

 of the iron is tested with potassium sulphocyanide, after acidifying with 

 hydrochloric acid ; 0-2 to 0-3 gr. of iron is deposited in three to four 

 hours. 



In a later paper Classen states that the most favourable condition for 

 the deposition of iron is with a current N.D.,o„=l-5 ampere at the ordi- 

 nary temperature. Neumann ' adds that weaker currents (0-3 to 05 ampere) 

 can be used, but then a larger proportion of ammonium oxalate must be 



' Tlworie u: Praxis der anahjtisolien Electrolyse dbr Metalled p. 114. 



