710 PHYSIOLOGICAL CHEMISTRY. 



of the dish, plus total solids, the quantity of total organic matter is 

 determined ; and by deducting weight of dish from weight of dish 

 plus ash, the total quantity of inorganic matter is found. 



The analysis of the ash is effected by the methods given in con- 

 nection with the consideration of the various acid and basic constitu- 

 ents themselves. Chlorine is determined by precipitating the solution 

 of the ash in nitric acid with silver nitrate, sulphuric acid by barium 

 chloride, phosphoric acid by ammonium molybdate, calcium by ammo- 

 nium oxalate, potassium by chloroplatinic acid, iron by potassium 

 ferrocyanide, etc. 



As the methods outlined above are too involved for clinical w r ork, 

 no details are given. Modern methods for quantitative urinary analy- 

 sis are practically all volumetric, and will be described for the various 

 constituents of the urine. 



Nitrogen in the urine. The nitrogen in the urine is derived di- 

 rectly from protein metabolized. As only a small part of the nitro- 

 gen is excreted in the feces and sweat, the estimation of the urinary 

 nitrogen is the most commonly used procedure for determining the 

 amount of protein broken down in the body. The total nitrogen 

 varies from 10 to 16 grammes a day, and, as indicated above, varies with 

 the protein metabolism. Thus it is increased with a heavy meat diet, 

 with fever, in diabetes, etc. The approximate distribution of the 

 urinary nitrogen is : 



Urea 85 per cent. 



Ammonia 5-6 per cent. 



Creatinine 4 per cent. 



Uric acid 0.5-1 per cent. 



Other nitrogen 3-5 per cent, (hippuric acid, xanthine 



bases, etc.). 



The estimation of nitrogen alone has little clinical value, but it is 

 frequently done in order to find the percentage of ammonia, which is 

 very valuable. The method used is the customary Kjeldahl method 

 (p. 445), using the Gunning mixture of sulphuric acid, sodium sul- 

 phate, and copper sulphate. 



Normal nitrogenous constituents of urine. The more important are 

 urea, uric acid, ammonia, creatiniiie (creatine). Less important are 

 the xanthine bases, hippuric acid, etc. 



Urea, Carbamide, CO(NH 2 ) 2 , or CO li <^ *. Urea, the most im- 

 portant constituent of urine, is the chief nitrogenous end-product of 

 the metabolism of proteins in the body, and carries off by far the 



