382 PHYSIOLOGICAL CHEMISTRY. 



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

 content of the urine under examination computed. 



The procedure is as follows : 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 cupric sulphate and boil the 

 mixture for some time after it is colorless (about one hour) . Allow 

 the flask to cool and dilute the contents with about 200 c.c. of water. 

 Add a little more of a concentrated solution of NaOH than is nec- 

 essary 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 con- 

 denser so arranged that the delivery-tube passes into a vessel con- 

 taining a known volume (the volume used depending upon the nitro- 

 gen content of the urine) of y\ 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 shak- 

 ing and distil the mixture until its volume has diminished about 

 one-half. Titrate the partly neutralized - sulphuric acid solution 

 by means of -^ sodium hydi oxide, using congo red as indicator, and 

 calculate the content of nitrogen of the urine examined. 



Calculation. Subtract the number of cubic centimeters of y^ 

 sodium hydroxide used in the titration from the number of cubic 

 centimeters of y^ sulphuric acid taken. The remainder is equiva- 

 lent to the number of cubic centimeters of -f-$ sulphuric acid, neu- 

 tralized by the ammonia of the urine. One c.c. of y\ sulphuric acid 

 is equivalent to 0.0014 gram of nitrogen. Therefore, if y repre- 

 sents the volume of urine used in the determination, and y' the 

 number of cubic centimeters of -^ sulphuric acid neutralized by the 

 ammonia of the urine, we have the following proportion : 



3/:ioo: :/X 0.0014:^ (percentage of nitrogen in the urine ex- 



amined). 



Calculate the quantity of nitrogen in the twenty- four hour urine 

 specimen. 



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. 



2 Powdered zinc may be substituted. 



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

 back " of the fluid. 



