464 PEACTICAL PHYSIOLOGY 



method, and the result expressed as total alloxuric nitrogen. This 

 result is exceedingly useful in studying the metabolism of alloxuric 

 bodies. If it be desired to determine the uric acid and the bases 

 separately, a slight modification of the process is necessary. 



Solutions necessary. 1. Magnesia mixture. This consists of 1 part 

 crystallised magnesium chloride, 2 parts chloride of ammonium, dis- 

 solved in 8 parts of water and made strongly alkaline with 4 parts of 

 ammonia. If the mixture be not quite clear (from the presence of 

 magnesium hydrate) more ammon. chlor. should be added. 



2. Ammoniacal silver nitrate. Dissolve 26 gr. silver nitrate in 

 about 300 c.c. water, add ammonia to this until the precipitate of 

 silver oxide, which first forms, redissolves. Dilute the solution to one 

 litre. 



3. Kjeldahl's apparatus and solutions. 



Determination. 240 c.c. proteid free urine are mixed with 30 c.c. 

 magnesia mixture, and the solution is made up to 300 c.c. by the 

 addition of a 20 per cent, ammonia solution. This process is best done 

 in a measuring cylindei. After the precipitate has settled, which it 

 does in a few minutes, it is filtered through a dry folded filter and two 

 portions of the filtrate are taken amounting to 125 c.c. each. Each 

 of these corresponds to 100 c.c. of the original urine. They are both 

 treated in exactly the same way, and should yield similar results. 

 Each is mixed with 10 c.c. ammoniacal silver nitrate, and the mixture, 

 after the precipitate has settled somewhat, filtered through an ash- 

 free filter paper (of 10 c.m. diameter), The last traces of the 

 precipitate are removed from the beaker by means of weak ammonia 

 water. The next stage consists in washing the precipitate with 

 distilled water until it is free from ammonia, as the presence of this 

 would vitiate the determination of the nitrogen. In order to do 

 this, the precipitate should be allowed to stand exposed to the air 

 over night so that it may become partially dried, in which state the 

 washing with water is much easier than when the precipitate is moist, 

 for then it forms a gummy mass. The washing must be continued 

 until the washings no longer react alkaline to litmus. In order to 

 remove the last traces of ammonia, the filter paper, with the precipi- 

 tate on it, is carefully removed to a Kjeldahl's combustion flask; 

 about 50 c.c. of water are added, and then a little magnesium oxide. 

 The mixture is then boiled whereby the magnesia expels the ammonia. 

 The boiling is continued until only about 10 c.c. of fluid remain, and 

 then sulphuric acid, etc., are added, and the nitrogen determined. 



To Determine the Bases and Acid separately, a large quantity of 

 urine (500 c.c.) is mixed with one-tenth its bulk of magnesium mix- 



