ANALYSIS OF URINE 559 



Gulick l has simplified this procedure by oxidising the material with 

 smaller quantities of sulphuric acid and potassium sulphate : 



The urine is diluted 4-10 times with an acid mixture consisting of 

 125 c.c. water, 40 c.c. sulphuric acid, 5 c.c. of saturated mercuric chloride 

 solution, 20 gm. of potassium sulphate and diluted to 200 c.c. with water, 

 so that -5 c.c. of the diluted urine contains from -4 to 7 mgm. of nitrogen. 



5 c.c. of this diluted urine are measured into a small oxidising flask, 

 which consists of a pear-shaped bulb of 15 c.c. capacity blown upon the end 

 of a glass tube and bent so that the bulb is at an angle to the tube when the 

 tube is placed in a vertical position. A bead or a spiral of platinum wire 

 4-5 mm. long is added and the solution is heated for at least i minute after 

 it has become clear ; the total time of oxidation is from 6-10 minutes. 

 When cool the contents of the flask are dissolved in water, washed into a 50 

 c.c. measuring flask and Nesslerised. 



The oxidation may also be effected with larger quantities of urine (i- 

 2 c.c.). They are heated in a flask of 25-50 c.c. capacity exclusive of the 

 neck with i c.c. of sulphuric acid, i gm. of potassium sulphate and 3 drops 

 of saturated mercuric chloride solution for 15-20 minutes, avoiding frothing. 

 The resulting mixture is dissolved in water and diluted to 100 c.c. in a 

 measuring flask. An aliquot part, 5 c.c. containing '35-*7 mgm., is re- 

 moved and Nesslerised in a 50 c.c. measuring flask. 



The Nesslerising may be effected with a solution containing 1 5 gm. of 

 mercuric iodide, 10 gm. of potassium iodide, 40 gm. of sodium hydroxide and 

 water to 500 c.c. The sodium hydroxide is dissolved in water and set 

 aside to cool ; the iodides are dissolved in about 15 c.c. of water, transferred 

 to the 500 c.c. flask with the aid of the alkali and the volume diluted to 

 500 c.c. The solution is transferred to a stoppered conical flask and the 

 precipitate allowed to settle or it may be filtered. This solution can be used 

 directly for quantities of nitrogen from o to i mgm. per 50 c.e. The standard 

 ammonium sulphate solution and the unknown are put into 50 c.c. volu- 

 metric flasks with about 40 c.c. of water, 5 c.c. of the reagent are added and 

 the solutions diluted to the 50 c.c. mark. The colour comparison should 

 be made within an hour. 



Bock and Benedict 2 have pointed out certain sources of error in the 

 Folin-Farmer method, but find that the results by the colorimetric method 

 are within 2 or 3 per cent, of those obtained by the ordinary Kjeldahl method. 

 They prefer to distil off the ammonia rather than aspirate and they connect 

 the test tube, to which water has been added, by rubber tubing to a condenser. 

 Distillation is also preferred by Pregl and by Wolf (see below). 



1 J. Biol. Chem., 1914, 18, 541. *lbid. t 1915, 20, 47. 



