484 PHYSIOLOGICAL CHEMISTRY 



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 delivery-tube passe! 

 into a vessel containing a known volume (the volume used depending upon th< 

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

 the delivery-tube reaches beneath the surface of the fluid. 1 Mix the content! 

 of the distillation flask very thoroughly by shaking and distil the mixture unti 

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

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

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



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

 hydroxide used hi the titration from the number of cubic centimeters of N/K 

 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. On< 

 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 numbei 

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

 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. 



Interpretation. An adult of medium size on a mixed diet will usuall} 

 excrete 12-18 grams of nitrogen per day. It varies, however, almosl 

 directly with the protein ingestion and hence usually runs parallel tc 

 the excretion of urea (see page 493). In a normal adult the totai 

 nitrogen of the feces and of the urine will often be almost exactly 

 equal to the total nitrogen of the food. Such a condition is called 

 "nitrogen equilibrium." The feces usually contain very little nitrogen, 

 (See also Ammonia, Creatinine, etc.) . 



Calculation of Percentage Nitrogen Distribution. In modern metabo- 

 lism studies where the various forms of nitrogen are determined, in 

 addition to the total nitrogen as yielded by the Kjeldahl method, it is 

 customary to indicate what portion of the total nitrogen was present in 

 the form of each of the individual nitrogenous constituents. These 

 percentage values are secured by dividing the weight (grams) of 

 nitrogen excreted for the day in the form of each individual nitrogenous 

 constituent by the weight of the total nitrogen output for the same 

 period. For example, if the total nitrogen excretion is 9.814 grams 

 and the excretion of urea-nitrogen is 8.520 grams and the excretions 

 of nitrogen in the forms of ammonia and creatinine are 0.271 gram and 

 0.639 gram respectively, the percentage distribution for these forms of 

 nitrogen would be calculated as follows: 



8.520 grams urea-nitrogen -f- 9.814 grams total nitrogen = 84. 3 per cent 



0.271 gram ammonia- nitrogen -f- 9.814 grams total nitrogen = 2. 7 per cent 

 0.639 gram creatinine- nitrogen -5- 9.814 grams total nitrogen = 6.5 per cent 



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

 of the fluid. 



