Glucose, so characteristic of diabetes mellitus, is not difficult of detection or estimation.  The facility with which it reduces alkaline cupric, argentic, bismuthous, ferric, mercuric salts, indigo and potassic picrate and chromate solutions has been utilized for the preparation of several ready methods for its determination.  Trommer’s test consists in adding enough cupric sulphate to color green, then excess of alkali, and boiling.  Yellow to brick-red cuprous oxide forms as a heavy precipitate if glucose is present.  The organic matter of the urine prevents the precipitation of cupric hydrate on the addition of the alkali.  This test is delicate and deservedly popular.  Fehling’s well-known solution contains sodio-potassic tartrate, which serves the purpose chiefly of retaining the copper in solution.  Unfortunately, Fehling’s original solution has a tendency to become hyper-sensitive if kept long, a proneness to change that is much increased on dilution.  When so altered, the solution will yield a more or less copious precipitate of cuprous oxide on merely boiling, and quite independent of the presence of glucose.  This decomposition is obviated by preserving the copper salt in a separate solution from the tartrate and alkali, and mixing before use.  Schmiedeberg substitutes mannite and Cresswell glycerin for the Rochelle salt, in order to render the solution stable.  Some prepared by the writer over twelve months ago, according to the suggestion of the latter physician, has since shown no signs of decomposition, and is now as good as it was then.  For qualitative purposes the solution may be prepared thus:  Dissolve 35 gm. of recrystallized cupric sulphate and 200 c.c. of pure glycerin in 100 c.c. of distilled water.  Dissolve separately 80 gm. of caustic soda in 400 c.c. of water.  Mix the solutions and boil for a quarter of an hour.  A small amount of reduction from impurity in the glycerin takes place.  Allow to stand till clear, decant, and dilute to 1,250 c.c.  Ten cubic centimeters will then equal roughly 5 centigrammes of glucose.  For exact quantitative determination it is necessary to standardize the solution with pure anhydrous dextrose.

To a practiced operator the indications yielded by the use of this test are of great value; but beginners are exceedingly liable to mistake its various reactions, and to report the urine as saccharine when normal traces only of sugar are present.  The bismuth test of Bottger, as greatly improved by Nylander, is fairly delicate, and not so easily misread as Fehling’s.  A large volume of reagent being used with a comparatively small quantity of urine, the precipitate of earthy phosphates does not interfere in the least with the reaction.  On boiling about 3 drachms of Nylander’s solution and 20 minims of urine for a minute or two, the liquid darkens with a trace of sugar, and becomes opaque and black if the latter is present in quantity.  The reagent is prepared by dissolving 494 grains of caustic soda, 247 grains of Rochelle salt, and 154 grains of subnitrate of bismuth (free from silver) in 13 fluid oz. of distilled water.  It should be decanted for use from any sediment.