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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 CO2 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 * 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 H2SO4)
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
H2SO4. 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 1^ 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.
Kxop-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. Chern. Soc, 30; Levene and Meyer,
ibid., 81; Gill, Allison and Grindley, ibid., 31; Henriques and Gammeltoft, Skand.
Arch. f. Physiol., 25.
:in and Pettibone, Journ. of Biol. Chem., 11.
’ Knop, Zeitechr. f. analyt. Chern., 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, Zeitechr. f. physiol. Chern., 84.
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