This test will give a distinct result only in presence of a minimum of 1 per cent. of sugar.
A much more sensitive test consists in the reduction of a salt of bismuth in an alkaline solution of urine sugar. This test, given by Böttcher, was modified in the following manner by Nylander. Four grammes of Seignette salts are dissolved in 100 cubic centimetres of soda lye of the sp. gr. 1.119, and 2 grammes of bismuth subnitrite are added to the fluid warmed in a water-bath. This solution represents Nylander’s reagent.
In order to use the test we mix five cubic centimetres of the urine to be examined (which, if possible, ought not to have a specific gravity higher than 1.020) with 0.5 cubic centimetre of Nylander’s reagent in a test-tube. The mixture is now boiled for two minutes. If more than 0.5 per cent. of sugar is present in the urine, the originally white precipitate of earthy phosphates becomes deep black; with 0.05 per cent. of sugar it shows a clear, brown color.
If this test is not the most sensitive of all, it provides us with a process for recognizing sugar in the urine, and not a number of other reducing substances mixed with it. (Neumeister.)
Amongst the various tests for sugar used in practice, that of Trommer is one of the most common.
We mix some 5 cubic centimetres of urine with an equal volume of 10 per cent. solution of potash or soda, and add to the mixture, drop by drop, a 10 per cent. solution of sulphate of copper, so long as the resulting hydrated oxide of copper is dissolved by the sugar.
In this way we get, according to the quantity of sugar contained, a more or less ultramarine-blue fluid. If we warm this, the result, in consequence of the reducing action, is a reddish-yellow precipitate of hydrated suboxide of copper which, after a short time, adheres to the sides of the test-tube, somewhat in the fashion of a mirror.