ADVANCED PHYSIOLOGICAL CHEMISTRY 463 



previously been brought to the boil in a wash bottle. In order 

 to remove the last traces of precipitate from the filter paper it is 

 necessary to open out the latter so that no precipitate remains in 

 the folds. 



The estimation of the uric acid contained in the solution of ammonium 

 urate thus obtained, may now be determined by one of two methods : 



1. Weighing the uric acid directly. For this method it is necessary 

 that the water used in the removal of the precipitate should not amount 

 to more than 30 c.c.; if more than this amount has been employed, 

 the liquid should be concentrated on the water-bath till this bulk has 

 been attained. The urate is now decomposed by adding 1 c.c. of HC1 

 (con.) and heating just to boiling point. The fluid is then set aside 

 for the uric acid to crystallise out, and this is collected on a weighed 

 filter (see p. 492), washed with cold distilled water, dried and weighed. 



2. Titrating the decomposed urate with standard potassium permanganate. 

 Since chlorides have a certain power of decolourising permanganates, it 

 is necessary that all traces of ammon. chlor. be removed from the 

 precipitate. This is accomplished by washing it with a saturated 

 solution of ammonium sulphate instead of ammonium chloride. The 

 contents of the filter are then transferred to a small Erlenmeyer flask by 

 means of a jet of hot water, and the volume brought up to 100 c.c., the 

 water employed for this purpose being also used to thoroughly wash out 

 the filter. Now add to the solution in the flask 15 c.c. concentrated 

 sulphuric acid, and immediately titrate with the permanganate. The 

 principle of the reaction is that the permanganate oxidises the uric acid, 

 and, in doing so, loses its colour ; whenever all the uric acid has been 

 oxidised the permanganate will retain its red colour. The standard 

 solution is, therefore, run into the acidified solution, when it will be 

 noticed that, on the first additions, the red colour immediately dis- 

 appears, but that, as more and more is added, the red takes longer to 

 disappear, until at last a drop of the permanganate retains its colour 

 and gives to the fluid on shaking a diffused pink flush. This is the end 

 reaction. The number of c.c. used is now read off, and the amount of 

 uric acid is thus calculated. For clinical purposes the titration method 

 is certainly the one to be employed, the only part about which there 

 is any difficulty (on account of its slowness in filtering) being the 

 washing of the precipitate with ammonium sulphate solution. 



The Estimation of the Total Alloxuric Bodies. Modified Camerer's 

 Method. Principle. Ammoniacal silver nitrate* in the presence of 

 neutral salts, or better, of magnesium mixture, combines with all the 

 alloxuric bodies to form an insoluble salt of definite composition 

 (see p. 206). The nitrogen in this can be estimated by Kjeldahl's 



