URINE 505 



monium sulphate by boiling with concentrated sulphuric acid, the 

 subsequent decomposition of the ammonium sulphate by means of 

 a fixed alkali (NaOH) and the collection of the liberated ammonia in 

 an acid of known strength. Finally, this partly neutralized acid solu- 

 tion is titrated with an alkali of known strength and the nitrogen 

 content of the urine under examination computed. 



Procedure. Place 5 c.c. of urine in a 500 c.c. long-necked Jena glass 

 Kjeldahl flask, add 20 c.c. of concentrated sulphuric acid and about 0.2 gram 

 of copper sulphate and boil the mixture for some time after it is colorless 

 (about one hour). If a suitable hood or fume chamber is not available the 

 sulphuric acid vapors may be carried away by suction. Connect the outlet tube 

 of a 2-3 liter wash bottle filled with caustic soda solution with a suction pump. 

 The inlet tube is connected with a Folin fume absorption tube such as illustrated 

 in Fig. 158. If such a tube is not at hand a small funnel 

 may be attached. The absorption tube is placed loosely 

 over the mouth of the digestion flask and a constant current 

 of air drawn through the apparatus. 



Allow the flask to cool and dilute the contents with 

 about 200 c.c. of ammonia-free water. Add a little more 

 of a concentrated solution of NaOH than is necessary to 

 neutralize the sulphuric acid 1 and introduce into the flask 

 a little coarse pumice stone or a few pieces of granulated 

 zinc, 2 to prevent bumping, and a small piece of paraffin to 

 lessen the tendency to froth. By means of a safety-tube 



connect the flask with a condenser so arranged that the _ 



. . , FIG. 158. FOLIN 



delivery-tube passes into a vessel containing a known FUME ABSORBER. 



volume (the volume used depending upon the nitrogen 

 content of the urine) of N/io sulphuric acid, using care that the end of the 

 delivery-tube reaches beneath the surface of the fluid. 3 Mix the contents of 

 the distillation flask very- thoroughly by shaking and distil the mixture until 

 its volume has diminished about one-half. Titrate the partly neutralized N/io 

 sulphuric acid solution by means of N/io sodium hydroxide, using congo red as 

 indicator, and calculate the content of nitrogen of the urine examined. 



Calculation. Subtract the number of cubic centimeters of N/io sodium 

 hydroxide used in the titration from the number of cubic centimeters of N/io 

 sulphuric acid taken. The remainder is equivalent to the number of cubic centi- 

 meters of N/io sulphuric acid, neutralized by the ammonia of the urine. One 

 c.c. of N/io sulphuric acid is equivalent to 0.0014 gram of nitrogen. Therefore, 

 if y represents the volume of urine used in the determination, and y' the number 

 of cubic centimeters of N/io sulphuric acid neutralized by the ammonia of the 

 urine, we have the following proportion : 



y: ioo::y'Xo.ooi4: x (percentage of nitrogen hi the urine examined). 



Calculate the quantity of nitrogen in the 24-hour urine specimen. 



1 This concentrated sodium hydroxide solution should be prepared in quantity and 

 "check" tests made to determine the volume of the solution necessary to neutralize the 

 volume (20 c.c.) of concentrated sulphuric acid used. 



a Powdered zinc may be substituted. 



3 This delivery- tube should be of large caliber in order to avoid the "sucking back" 

 of the fluid. 



