URINE 485 



Nitrogen Partition in Urines Containing Albumin. If the urine to 

 be tested contains albumin this must be removed before an attempt at 

 a nitrogen partition is made. This may be done by heating to boil- 

 ing, acidifying with acetic acid to coagulate the protein, filtering and 

 making up the filtrate to the original volume of the urine. If very small 

 amounts of albumin are present this is attended with difficulty. In 

 these cases Tracy and Welker 1 have suggested the use of aluminium 

 hydroxide cream. It apprently removes none of the nitrogenous con- 

 stituents of normal urine. 



Procedure. One liter of urine (containing not over i per cent of albumin) 

 is mixed with one liter of aluminium cream 2 and filtered. 



2. Folin-Farmer Microchemical Method. 3 Principle. This 

 method belongs with the so-called microchemical methods inasmuch as 

 it is adapted to the determination of amounts of nitrogen in the neigh- 

 borhood of i mg. while in the ordinary Kjeldahl procedure 30-100 mg. 

 of nitrogen are generally manipulated. One c.c. of diluted urine is 

 decomposed with sulphuric acid as in the Kjeldahl method, the am- 

 monia formed is set free by the addition of alkali and carried over into 

 an acid solution by means of a current of air. The ammonia solution 

 is then treated with the Nessler-Winkler reagent and the color produced 

 compared with that of a standard solution of an ammonium salt 

 treated in the same way. 



Colorimeter. For this method as well as for a number of other 

 methods commonly used in urinary and blood analysis an instrument 

 known as a colorimeter is required. Through its aid we are able ac- 

 curately to measure the respective depths of color in two solutions and 

 hence to calculate the comparative amounts of substances, which form 

 colored compounds in a quantitative manner. The most satisfactory 

 instrument for this purpose is the Duboscq colorimeter (see Fig. 153, 

 page 486). This enables the two colored solutions to be compared in 

 the same optical field and with a degree of accuracy of about i per 

 cent. The later type of the Duboscq colorimeter with cylinders instead 

 of prisms movable is to be preferred, particularly as this type may be 

 readily adapted to the comparison of cloudy solutions or suspensions, 

 the instrument thus modified being called a nephelometer (see Fig. 83, 

 page 291). In this later form of colorimeter the depths of the colored 



1 Tracy and Welker : Jour. Biol. Chem. 22, 55, 1915; For other applications of alu- 

 minium hydroxide precipitation of colloids, see Welker and Marshall, /. Am. Chem. Soc., 

 25, 820, 1913. 



2 Aluminium Hydroxide Cream. To a i per cent solution of ammonium alum at room 

 temperature add a slight excess of a i per cent solution of ammonium hydroxide. Wash by 

 decantation until the wash water shows only the faintest trace of residue on evaporation. 

 Stronger solutions should not be used. 



3 Folin and Farmer: Jour. Biol. Chem., n, 493, 1912. 



