0\ THE ELECTROLYTIC METHODS OF QUAXTTTATTVE ANALYSIS. 185 



rated qualitatively from iron or other metals, which are deposited at the 

 cathode in the electrolysis of their solutions, with greater certainty than 

 by the ordinary analytical methods. 



C. The Electrolytic Determination of Iron in Urine and other Animal Products. 

 Bij Charles A. Kohn, M.!Sc., Ph.D., and G. C. Clat'xon, Ph.D. 



Iron is the only heavy metal present in the body, and the part it plays 

 in animal metabolism is of special interest. The varied conditions of its 

 combinations can as yet only be approached by histochemical reactions ; 

 for its total and quantitative determination the ordinary volumetric, 

 gravimetric, or colorimetric methods have been applied. As the 

 quantities present in certain organs and excreta are extremely small, 

 special importance attaches to the methods adopted for their estimation. 

 The usual method of procedure is to dry and ignite the product to 

 be tested, extract the residue with acid, and determine the iron in 

 the resulting solution. In the case of urine, for instance, a day's 

 discharge (about 1,500 c.c.) is evaporated and ignited until the 

 residual ash is quite white, then dissolved in sulphuric acid and titrated 

 with a dilute permanganate solution, after reduction with sulphurous 

 acid (Hamburger •) or with zinc (Damaskin,-' JoUes ^). Gottlieb and 

 Ludwig '^ employed a gravimetric method in which the iron is precipi- 

 tated as Prussian blue in presence of a 1 per cent, zinc chloride solution, 

 the precipitate subsequently decomposed by alkali, and the resulting ferric 

 hydrate weighed after separation from the zinc by repeated precipitation 

 with_ ammonium hydrate. More recently Jolles has recommended the 

 gravimetric determination of iron in urine by precipitation with nitroso- 

 fi naphthol.-' The great variations obtained by the adoption of these 

 methods are shown in the following data as to the quantity of iron present 

 in a day's discharge of normal urine : — 



Hamburger 



Gottlieb and Ludwi'c 



Lieber and Mohr . 



Damaskin 



Jolles 



Kumberg- 



7-C to 14o mgr. per 24 hours. 



l-.o9 to 3-60 



0-S to 1-7 



0-5 to 1-5 



4-6 to 9-1 



0-47 to 1-15 



The values found by Damaskin, Lieber and Mohr, and Kumberg are 

 usually regarded as the most correct, and 1 mgr. iron per diem in normal 

 urine is looked upon as the average amount.'' 



Two sources of error beset these methods of analysis. In the first 

 place, the very large quantity of iiaineral salts, especially chlorides and 

 phosphates, left after ignition has a disturbing influence on the titration 

 with permanganate, especially with such small proportions of iron as 

 1 mgr. in the total solution ; secondly, it is impossible to completely 

 remove the organic matter in the ignition, and its presence in solution 

 affects the titration to a marked extent. These errors, which are of 

 necessity irregular in character, are still more serious when gi-avimetric 



o"- 



' Robert, Pharmah. Miftnl. ,1891, 7, 40. 



- Arbeifmd. pharmalwlog. Inst., Dorpat, 1871, and i^eits. ayial. CJiem., 1892, 31, 

 481. 



^ Zcits. anal. Chen., 1897, 36, 149. ' Arclih-f. e.rpt. Pathdogle. 1889, 27, 139. 

 ■■' Luc. fit. '■> stockman, Prit. Med. .Joimi., 1893. 



