690 URINE. 



After cooling it is diluted to about f to 1 liter with water, the ammonia 

 completely distilled off, after making it alkaline with caustic soda, and 

 the ammonia collected in standard acid. After boiling in order to drive 

 off the C02 and cooling, the acid is retitrated. 



In recent years objections of various kinds have been made against 

 these methods, which are directed towards their exactness and which have 

 led to changes in several directions (BENEDICT and GEPHART, LEVENE 

 and MEYER, GILL, ALLISON and GRINDLEY). These changes are: 

 precipitation of the other nitrogenous substances (nearly all the ammonia) 

 with phosphotungstic acid, decomposition of the urea in the nitrate by 

 heating with acid in an autoclave to 150, and distilling off the ammonia 

 from the solution, made alkaline, not by boiling with alkali, but by the 

 aid of a vacuum or by means of a current of air. These changes have 

 been carefully studied by HENRIQUES and GAMMELTOFT 1 and they have 

 suggested the following method: 



Henriques and Gammeltoft Method. First determine in 5 cc. urine 

 how much of a 10 per cent phosphotungstic acid solution (in N/2 H^SCU) 

 is necessary to exactly cause a complete precipitation. Then place 10 cc. 

 of the urine in a 100 cc. flask, add the determined quantity of phospho- 

 tungstic acid solution and fill the flask up to the 100 cc. mark with N/2 

 H2S04. The liquid is allowed to stand after mixing until it has settled 

 and it is then filtered. Two portions of 10 cc. each are placed in test- 

 tubes of Jena glass, covered with tin-foil and placed in the autoclave at 

 150 C. for 1J hours. The contents of the test-tubes are now placed in a 

 flask, and the ammonia determined either by passing a current of air 

 through it (after the addition of sodium carbonate) or by distillation in a 

 vacuum (after the addition of barium hydrate dissolved in methyl alcohol) . 

 FOLIN and PETTIBONE 2 have suggested a method, according to which the 

 ammonia is determined colorimetrically with Nessler reagent. 



KNOP-HUPNER'S method 3 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 686). This method 

 is less accurate than the preceding ones, and therefore in scientific work it is dis- 

 carded. 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 number of different appa- 

 ratus have been constructed to facilitate the use of this method. 



1 Benedict and Gephart, Journ. of Amer. Chem. Soc., 30; Levene and Meyer, 

 ibid., 31; Gill, Allison and Grindley, ibid., 31; Henriques and Gammeltoft, Skand. 

 Arch. f. Physiol., 25. 



2 Folin and Pettibone, Journ. of Biol. Chem., 11. 



3 Knop, Zeitschr. f. analyt. Chem., 9; Hiifner, Journ. f. prakt. Chem. (N. F.), 3. 

 In regard to the extensive literature, see Huppert-Neubauer, 10. Aufl., 304, and follow- 

 ing. See also Keogh, Zeitschr. f. physiol. Chem., 84. 



