A manual of clinical medicine and physical diagnosis / by Thomas Hawkes Tanner.

Date:
1869
Catalogue details

Licence: Public Domain Mark

Credit: A manual of clinical medicine and physical diagnosis / by Thomas Hawkes Tanner. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    Urine containing: an Excess of Urea maybe known by its nigh specific gravity—1020 to 1035—and by crystals of nitrate of urea forming on adding nitric acid to a por- tion of the urine in a test-tube. If the urea be only slightly in excess, the urine should be concentrated, by evaporation to about one-third its bulk, before adding the acid. Quantitative Determination of Urea (after Liebig).— It is very important that the student should know how to carry out this investigation. Urea is thrown down from its solution by mercuric nitrate (nitrate of mercury), and the precipitate so formed consists of four equivalents of mercuric oxide (oxide of mercury) to one equivalent of urea. On the knowledge of this fact the process for estimating urea quantitatively is based. But in order to arrive at accurate results, the urine subject to examination should first be freed from albumen, if it contain any, and from phosphates and sulphates. It is also necessary to make allowance for the chlorides which enter into its composition; for they, in presence of urea, prevent its combination with mercuric nitrate. The mercuric nitrate added to the urine reacts first on the chlorides, breaking them up into sodic nitrate (nitrate of soda), potassic nitrate (nitrate of potash), and mercuric chloride (chloride of mercury), and then com- bines with urea, forming a white insoluble compound of the composition already mentioned. Should, however, more mercuric nitrate be added to the urine than just enough both to decompose all its chlorides and to combine with all its urea, then the excess will remain in solution ; and to recognise its presence a solution of sodic carbonate (carbonate of soda), is required ; for sodic carbonate strikes a yellow colour, due to the liberation of the hydrated mercuric oxide (oxide of mercury) with mercuric nitrate. Thus the exact point is attained and just passed over as regards the precipitation of the urea, when the urine under examination, or any mixture containing urea, to which mercuric nitrate has been added, strikes a yellow colour when brought into contact with a solution of sodic carbonate. Three solutions then are necessary for the estimation of nrea quantitatively—viz. (a) the mercuric nitrate ; (b) the baryta (for phosphates and sulphates); and (c) the sodic carbonate solution.