346 PHYSIOLOGICAL CHEMISTRY. 



case a correction must be made (according to SCHLOSING'S 

 method) for the ammonia pre-existing in the urine. PFLUGER 

 and BLEIBTREU have essentially changed this method in the fol- 

 lowing way : They precipitate the other nitrogenized urinary con- 

 stituents with hydrochloric acid and phospho-tungstic acid, make the 

 filtrate faintly alkaline with milk of lime, determine the pre-existing 

 ammonia in a part of this filtrate according to SCHLOSING'S 

 method (observing certain precautions), and then placing the other 

 part of the filtrate (about 15 c. c.) in a large flask which contains 

 10 grms. crystallized phosphoric acid, heat fo 230-260 C. for 

 about three hours. All the urea is decomposed, and the ammonia 

 split off combines with the phosphoric acid. After cooling, an 

 excess of caustic soda is added and the ammonia distilled into a 

 titrated acid, which must then be retitrated. After subtracting the 

 quantity of pre-existing ammonia very accurate results are obtained 

 for the ammonia originating from the urea (and perhaps from an 

 unknown ureid present in the urine). 



KNOP-HUF^ER'S METHOD is based on the fact that urea by the 

 action of sodium hypobromite splits into water, carbon dioxide 

 (which dissolves in the alkali), and nitrogen, whose volume is 

 measured (see page 340). This method is less accurate than the 

 preceding ones, and therefore in scientific work it is discarded. It 

 is of value to the physician and for practical purposes because of 

 the ease and rapidity with which it may be performed, even though 

 it may not give very accurate results. For practical purposes a 

 series of different apparatus have been constructed to facilitate 

 the use of this method. Among these the ureometer of ESBACH 

 deserves to be especially mentioned. 1 In regard to the reagents 



1 Dr. CHAS. A. DOREMUS has constructed a ureometer of the very simplest 

 kind. It consists of two parts. First, a vertical glass tube closed at the top 

 and bent sharply below, where it expands into a bulb having an orifice at its 

 upper part. Secondly, a pipette with an elastic rubber nipple. Both parts 

 are graduated ; the vertical tube so as to show the quantity of urea (as indi- 

 cated by the volume of nitrogen) in each cubic centimetre of urine tested, 

 while the pipette is graduated so as to show one cubic centimetre. The 

 instrument is used thus: First the vertical tube is filled with the alkaline 

 sodium-hypobromite solution in the following manner : holding it vertically, 

 the operator pours the solution into the bulb, and when it is rather more than 

 half full he inclines the apparatus horizontally until the entire tube is filled 

 and a little left in the bulb say one third or thereabouts. Then he restores 

 it to the vertical position. He now draws into the pipette, by means of the 



