Earthy phosphates then fall
naturally out of solution, so that the putrid fluid is always well
furnished with sediment. Nitrogen that has served its purpose as
muscle or other proteid leaves the animal economy chiefly in the form
of urea, and its proportion in the urine, therefore, is a fair index
of the activity of wasting influences.
For its determination Knop's sodic hypobromite method, on account of
its convenience, is now generally preferred. The volumetric process of
Liebig, which depends on the formation of an insoluble compound of
urea with mercuric nitrate, possesses no advantages and is troublesome
to work. The principle of the hypobromite process is simple. In a
strongly alkaline solution urea is broken up by sodic hypobromite, its
nitrogen being evolved in the gaseous state, and its carbon and
hydrogen oxidized to carbonic anhydride and water respectively. The
volume of free nitrogen obtained bears a direct ratio to the amount of
urea decomposed.
[Illustration]
Among the number of instruments which have been introduced for the
purpose of conveniently measuring the evolved gas, that of Gerrard, an
illustration of which we give, is one of the simplest, cheapest, and
best.
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