246 THE URINE. 



Sodium hydrate solution (27 per cent.) is then added until the greater 

 portion of the acid is neutralized. The fluid is allowed to cool again, 

 and a few pieces of granulated zinc or a little talcum is thrown in, 

 when a mixture of the hydrate solution and of a 4 per cent, solution 

 of potassium sulphide is further added in excess. 1 Of either solution, 

 40 c.c. are added in all. The addition of the latter is necessary, as 

 the mixture not only contains ammonium sulphate, but also amino- 

 compounds of mercury, which latter would not give up their entire 

 amount of nitrogen if sodium hydrate alone were present. The talcum 

 or zinc merely prevents an unduly violent bumping when boiling. 

 The retort is immediately connected with a condenser through the 

 intervention of a Kjeldahl distilling tube. The condensing tube 

 dips into a nitrogen bulb, which contains a carefully measured 

 amount of a one-fourth normal solution of sulphuric acid ; 30 c.c. 

 are usually sufficient. The mixture is now distilled until about 

 two-thirds have passed over. The condenser is rinsed with a 

 little distilled water, which is added to the distillate. After the 

 addition of a few drops of tincture of cochineal the excess of 

 acid is retitrated with a one-fourth normal solution of sodium 

 hydrate. The difference indicates the amount of acid which was 

 consumed in uniting with the liberated ammonia. As 1 c.c. of the 

 one-fourth normal solution represents 0.0035 gramme of nitrogen, 

 the amount contained in the 5 c.c. of urine is ascertained by multi- 

 plying the number of cubic centimeters employed by this figure, 

 from which the total amount of twenty-four hours is then readily 

 calculated. The corresponding amount of albumin is obtained by 

 multiplying this figure by 6.25. 



Uric Acid. 



Whereas in mammals, the amphibia, and fishes urea is the most 

 important end-product of nitrogenous metabolism, the greater por- 

 tion of the urinary nitrogen in birds and reptiles is eliminated as 

 uric acid. 



Origin. The formation of uric acid in birds and reptiles is analo- 

 gous to the formation of urea in the mammal. This is true at least 

 of the greater portion, while a variable fraction originates from the 

 nucleins, viz., the xanthin bases. Organic ammonium salts, ammo- 

 acids, urea, and ammonium carbonate, when given to birds in their 

 food, appear in the urine as uric acid and are transformed into uric 

 acid in the liver. After extirpation of the liver almost all the uri- 

 nary nitrogen appears in the form of ammonia, in association with 



1 Neuberg has suggested that it is more com'enient to add about 1 gramme of sodium 

 thiosulphate to the caustic alkali solution for every 0.4 gramme of oxide of mercury, instead 

 of the sulphide, as the latter must always be prepared anew, and as the addition of the cor- 

 responding amount of liquid prolongs the distillation. In the alkaline solution the amino- 

 mercuric sulphate is then decomposed according to the equation : 



/NH 3 

 Hg/ \S0 4 + Na 2 S 2 3 + H 2 - HgS + (NH 4 ) 2 SO 4 + 



