ADVANCED PHYSIOLOGICAL CHEMISTEY 465 



ture, the precipitated phosphates filtered off, and an aliquot part of the 

 filtrate mixed with ammoniacal silver nitrate. The resulting precipitate 

 of all the alloxuric bodies is collected on a filter paper, washed, trans- 

 ferred to a beaker, and decomposed by boiling it with a solution of 

 sulphide of potassium prepared of such a strength that 10 c.c. are 

 necessary for every 100 c.c. urine employed. 1 The sulphide of 

 silver which is hereby formed is removed by filtration, and the filtrate 

 acidified with hydrochloric acid, and slowly evaporated to small 

 bulk (10 c.c.). The fluid is allowed to stand a few hours, when all 

 the uric acid will have crystallised out. This is collected on a weighed 

 filter, washed with cold water, and determined gravimetrically ; or, it 

 may be dissolved in an alkali and determined by the permanganate 

 method. The filtrate from which the uric acid has been separated, 

 combined with the water used to wash the latter, is made strongly 

 alkaline with ammonia, and the bases are precipitated by adding silver 

 nitrate. The precipitate is collected on an ash-free filter paper, washed 

 free of ammonia, boiled in a Kjeldahl's flask with magnesia and water 

 and the basic nitrogen determined. 1 gramme of nitrogen corresponds 

 to 2*62 grammes xanthin. 



As has been explained in the elementary course, it is of primary 

 importance not only to know how much total alloxuric nitrogen is 

 being excreted in the urine, but also, how much is being taken in the 

 food. It is then possible to determine how much alloxuric nitrogen is 

 derived from the tissues, or, in other words, we determine the endo- 

 genous moiety. There can be no doubt that it is owing to the neglect of 

 this precaution, that there exist so many discordant observations con- 

 cerning the metabolism of uric acid in health and in disease. It is of 

 little use to know that the uric acid is greater in one person than in 

 another for the difference may simply be due to the diet ; on the other 

 hand, a difference in the endogenous moiety would indicate a correspond- 

 ing difference in the metabolism of the tissue nucleins. 



CHAPTER XII. 

 URINE CONTINUED. 



Creatinin: Quantitative Determination (Salkowski's Method). 

 Principle. An alcoholic extract of evaporated phosphate-free urine is 

 mixed with an alcoholic solution of zinc chloride, which combines with 



1 Potassium sulphide solution. Dissolve 15 gr. KOH in a 1000 c.c. distilled 

 water ; divide the solution into two equal parts and saturate one of these with 

 H 2 S gas ; now mix the two halves. 



2G 



