URINE 483 



2. Calculation by Long's Coefficient. The quantity of solid material contained 

 in the urine excreted for any 24-hour period may be approximately computed by 

 multiplying the second and third decimal figures of the specific gravity by 2.6. 

 This gives us the number of grams of solid matter in i liter of urine. From this value 

 the total solids for the 24-hour period may easily be determined. 



Calculation. If the volume of urine for the 24 hours was 1120 c.c. and the spe- 

 cific gravity 1.018, the calculation would be as follows: 



(a) 18X2.6 = 46.8 grams of solid matter in i liter of urine. 



... 46.8X1120 



(b) - =52.4 grams of solid matter in 1120 c.c. of urine. 



Long's coefficient was determined for urine whose specific gravity was taken 

 at 25C. and is probably more accurate, for conditions obtaining in America, than 

 the older coefficient of Haeser, 2.33. 



Interpretation. See above. 



Total Nitrogen 



i. Kjeldahl Method. 1 Principle. The principle of this method is 

 the conversion of the various nitrogenous bodies of the urine into am- 

 monium sulphate by boiling with concentrated sul- 

 phuric 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 solution 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 concen- 

 trated 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. 152. 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 am- 

 monia-free water. Add a little more of a concentrated solution of NaOH than is 

 necessary to neutralize the sulphuric acid 2 and introduce into the flask a little 

 coarse pumice stone or a few pieces of granulated zinc, 3 to prevent bumping, and a 



1 There are numerous modifications of the original Kjeldahl method; the one described 

 here, however, has given excellent satisfaction and is recommended for the determination of 

 the nitrogen content of urine. 



2 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. 



3 Powdered zinc may be substituted. 



