URINE 



phate 1 in a second volumetric flask. Nesslerize both solutions as nearly as 

 possible at the same time with 5 c.c. of Nessler-Winkler solution 2 diluted, imme- 

 diately before'using, with about 25 c.c. of ammonia-free water to avoid turbidity. 

 Immediately fill the two flasks to the mark with ammonia-free water, mix well 



FIG. 163. FIG. 164. 



FIGS. 163 AND 164. FORMS OF APPARATUS USED IN METHODS OF FOLIN AND ASSOCI- 

 ATES FOR DETERMINATION OF TOTAL NITROGEN, UREA AND AMMONIA. (From Jour. Biol. 

 Chem. vol. n, 1912.) 



and determine the relative intensity of the two colors by means of a Duboscq 

 colorimeter. 8 



1 Care should be taken to secure the pure salt. All ammonium salts contain pyridine 

 bases which titrate like ammonia but do not react with Nessler's reagent. Pure ammonium 

 sulphate may be prepared by decomposing a high-grade ammonium salt with sodium hy- 

 droxide and passing the liberated ammonia into pure sulphuric acid. The salt is then pre- 

 cipitated by means of alcohol, then brought into solution in water and re-precipitated by 

 alcohol. The final product should be dried in a desiccator over sulphuric acid. Dr. H.L. 

 Emerson of Boston prepares a salt which is very satisfactory for use in this method. 

 According to Bock and Benedict, Kahlbaum's "Zur Analyse" ammonium chloride is 

 satisfactory. 



2 Chem. Zeit., 1899, p. 541. The Nessler-Winkler solution has the following formula: 



Mercuric iodide 10 grams. 



Potassium iodide 5 grams. 



Sodium hydroxide 20 grams. 



Water 100 c.c. 



The mercuric iodide is rubbed up in a small porcelain mortar with water, then washed 

 into a flask and the potassium iodide added. The sodium hydroxide is dissolved in the 

 remaining water and the cooled solution added to the above mixture. The solution cleared 

 by standing is preserved in a dark bottle. 



The 25 c.c. portion of the diluted reagent should be added about one-third at a time to 

 the contents of the flask. It is very essential that the dilution of the reagent takes place 

 immediately preceding its use, inasmuch as the diluted reagent deteriorates in a few minutes as 

 is indicated by the formation of a brick-red precipitate. Fortunately the reagent does not 

 decompose in this manner in the presence of the ammonium salt. 



3 The standard may be set at any desired depth but a very satisfactory depth is 20 mm. 

 The depth should be uniform throughout any series of comparative tests. 



