ANALYSIS OF URINE 547 



Iron. 



The amount of iron in urine (and tissues) is generally so small that at least 

 500 c.c. of urine must be used. 



The organic matter is first removed by oxidation : 



(1) By evaporating and igniting the residue. It is best to ignite, then to 

 dissolve the residue in some concentrated hydrochloric acid, filter from unburnt 

 carbon, ignite the filter paper and carbon residues and dissolve the ash in hy- 

 drochloric acid. Any reduced iron may be oxidised by boiling the solution 

 for 10 minutes with a drop of hydrogen peroxide. 



(2) By oxidation with nitric acid and sulphuric acid (p. 545). The oxida- 

 tion of large quantities of urine with nitric acid and sulphuric acid is best 

 effected by mixing the urine with one-tenth of its volume of nitric acid and 

 gradually adding this mixture to the sulphuric acid. 



The volumes of acid used must be noted and the reagents must be 

 analysed for their content in iron : 



A large quantity (500 c.c.) is evaporated in a platinum basin or round- 

 bottom flask to 5 or 10 c.c. In the case of nitric acid it must be removed by 

 evaporation several times with a measured quantity of sulphuric acid (10-20 c.c.) 

 of known iron content until sulphur dioxide is evolved. In the case of 

 hydrochloric acid the several final evaporations are not necessary. The pure 

 acids were found by Jahn to contain : 



1045 mg. Fe in 1000 c.c. H 2 SO 4 

 1080 HC1 



1704 HN0 3 



Of the various methods for estimating small quantities of iron the best 

 seems to be the titanium chloride method which depends upon the reaction : 

 TiCl 3 + FeCl 3 = TiCl 4 -j- FeCl 2 



Jahn l has worked out the details for its use with physiological liquids 

 and tissues : 



1 i ) The Preparation of a Standard Iron Solution. 



Instead of using ferrous ammonium sulphate it is more convenient to use 

 pure ferric oxide (ICahlbaum). The oxide is heated at 150 for 5 hours to 

 remove the last traces of water. 0*14297 gm. ( = *i gm. Fe) are placed in a 

 round bottom flask and dissolved by heating in 20 c.c. of concentrated sulphuric 

 acid and 200 c.c. of water. The flask is shaken on account of bumping, 

 allowed to cool several times, water lost by evaporation being replaced. The 

 clear solution is diluted to 1000 c.c. (i c.c. = 0*0001 gm. of Fe). 



(2) Preparation and Standardisation of the Titanium Chloride 

 Solution. 



10 c.c. of commercial 15 per cent, titanium chloride solution are gently 

 boiled in a very small beaker with 10 c.c. of pure concentrated hydrochloric 

 acid. The vapours are tested for hydrogen sulphide with lead acetate paper ; 

 if it be present the solution is boiled till it has been removed The solu- 

 tion is rapidly cooled and diluted in a flask to 2000 c.c. with boiled out water. 

 Owing to its being so easily oxidised it must be kept in an atmosphere of 

 hydrogen prepared in a Kipp apparatus and freed from hydrogen sulphide by 

 passage through permanganate. The flask is therefore fitted with a rubber 

 stopper with two holes ; the tubes through the stopper pass to the bottom. 

 Hydrogen is passed through one tube and the other tube is connected to a 

 burette. The burette is also connected with the hydrogen apparatus. 



The titration must be carried out in an atmosphere free from oxygen and 

 is effected most conveniently in a 250 c.c. filter flask, through which by the 

 side tube a current of carbon dioxide is passed ; the end of the burette 

 should reach below the level of the side tube. 



a Z. physiol. Chem., 1911, 75, 308. i& * 



