160 THE URINE. 



Have also at hand: 



1. Sulphuric acid, sp. gr. 1.84, free from compounds of nitro- 

 gen. 



2. Yellow mercuric oxid. 



3. Powdered potassium permanganate. 



4. Crystallized sodium thio-sulphate. 



II. Operation. With a pipette measure accurately 5 cubic 

 centimeters of urine. Place it in a flask holding about 250 cubic 

 centimeters, best of hard (Bohemian) glass. Add 0.4 gramme of 

 mercuric oxid and 10 cubic centimeters of the concentrated sul- 

 phuric acid. Lay the flask in a slanting position on a wire gauze 

 over a flame small enough to just bring it to boiling. Perform this 

 operation under a hood or where there is a good draft to carry away 

 the fumes of the acid. Continue the heating until the liquid is 

 colorless or straw-colored, which may require from thirty minutes 

 to an hour. Then remove the flask from the flame and very 

 slowly add to it a small amount of the powdered permanganate 

 until it is colored reddish or greenish. Allow it to cool and pour 

 it into an 800-cubic-centimeter flask which contains from 200 to 

 300 cubic centimeters of distilled water, rinsing the small flask 

 into the large one. The organic matter has been oxidized in this 

 process, the nitrogen being converted into ammonia, which is con- 

 tained in solution as ammonium sulphate. 



The ammonia is now to be set free by sodium hydrate, then 

 distilled into a known amount of standard acid, and its amount 

 found by ascertaining the loss of strength of the acid through its 

 neutralization by the ammonia. For this purpose a Liebig con- 

 denser is to be arranged so that the flask can be connected with 

 the upper end by means of a bent tube; this should be at least 

 Y 4 inch in diameter inside and a foot long, to prevent small drops 

 of the boiling liquid's being carried over. The insertion of a bulb 

 between the flask and condenser, also having the lower end of the 

 bent tube, in the flask, cut off obliquely, will aid in preventing this. 

 Add, now, to the liquid in the flask a few fragments of granulated 

 zinc to make it boil more quietly, about a gramme of sodium thio- 

 sulphate to precipitate the mercury, and 80 cubic centimeters of 

 the sodium hydrate, or enough to make it alkaline. Connect 

 immediately with the condenser through which a stream of cold 

 water is flowing and distill into a 400 or 500 cubic centimeter 



