r S PHYSIOLOGICAL CHEMISTRY 



J 



3. Folin -Farmer Microchemical Method. 1 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 Xessler-Winkler reagent and the color produced 

 compared with that of a standard solution of an ammonium salt 

 treated in the same way. 



FIG. i6a DDBOSCQ COLOEHCETEK. 



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. 160, 

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

 1 Folin and Farmer,- Jour. Bid. Ckcm., u, 493, 1912. 



