URINE 



507 



of the urine is brought about by means of a mixture of phosphoric and 

 sulphuric acids aided by ferric chloride, and that the liberated ammonia 

 is distilled without the use of a condenser. In this manner the time 

 required for the completion of a determination is very much shortened. 



Procedure. Place 5 c.c. of urine in a 300 c.c. Kjeldahl flask (Pyrex), add 

 5 c.c. of phosphoric-sulphuric acid mixture, 2 2 c.c. of 10 per cent ferric chloride 

 solution, and 4 to 6 small pebbles or glass beads to prevent bumping. Boil 

 vigorously in a hood over a microburner. 3 The burner should give a strong 

 flame and the top of the burner should be not more than i cm. away from the 

 bottom of the flask. In 3 or 4 minutes the foam which forms at first will entirely 

 disappear and the flask will be filled with dense white fumes. When this stage 

 is reached (but no earlier) cover the mouth of the flask with a small watch glass 

 and continue the vigorous heating for 2 minutes. At 

 the end of 2 minutes dilute urines will be green or blue 

 and concentrated urines will be a light straw yellow, the 

 black carbonaceous matter being completely destroyed. 4 

 Turn the flame very low and continue the gentle boiling 

 process for 2 minutes. Remove the flame, let the flask 

 cool for 4 to 5 minutes (not longer), add 50 c.c. of 

 ammonia free water, then 15 c.c. of saturated sodium 

 hydroxide solution (50 to 55 per cent) and connect the 

 flask promptly, by means of a rubber stopper and 

 ordinary glass tubing, with a receiver containing from 

 35 to 75 c.c. of N/io acid together with enough water to 

 make a total volume of 150 c.c., and a drop or two of 

 alizarin red. (The arrangement of the distillation ap- 

 paratus is shown in Fig. 159). As soon as connection 

 with the receiver is made, apply the flame again at full 

 force, but not directly under the center of the flask 

 until the acid and alkali have had time to mix. The 



contents of the flask begin to boil almost at once and 4 to 5 minutes boiling trans- 

 fers all of the ammonia to the receiver. Under the conditions described the 

 temperature of the contents of the receiver reaches only 6s-7oC. Disconnect 

 the receiver and titrate the excess of acid with N/io alkali. If the distillate 

 is titrated without cooling it is essential that a faint red color shall be accepted 

 as the end point. The color will deepen on cooling and if time permits it is 

 better to cool the distillate in running water before titrating. 



Calculation. Same as Kjeldahl method (p. 505). 



Interpretation. Same as Kjeldahl method (p. 506). 



FIG. 159. FOLIN 

 WRIGHT DISTILLATION 

 APPARATUS. 1 



^olin and Wright: Jour. Biol. Chem., 38, 461, 1919. 



2 To 50 c.c. of 5 to 6 per cent copper sulphate solution add 300 c.c. of 85 per cent phos- 

 phoric acid and 100 c.c. of concentrated sulphuric acid. 



3 A very convenient clamp for holding the Kjeldahl flasks in position is the one listed as 

 No. 24598 in Arthur H. Thomas Company's catalogue. The microburner suggested by 

 Folin is listed under No. 1506 in Eimer and Amend's catalogue. 



4 This method as far as the destructive digestion is concerned is primarily intended for 

 urine only. It is not applicable to highly resistant materials, as for example milk, which 

 cannot be completely destroyed in 6 minutes. Urines containing much sugar belong in 

 this class. If 2 c.c. of fuming sulphuric acid are used in addition to 5 c.c. of the regular 

 reagent sugar urines are readily destroyed within the required heating period of 4 to 5 

 minutes. 



