[Illustration:  DR. PAVY’S APPARATUS.]

In those cases where the amount of glucose present is required to be determined, Dr. Pavy’s ammonia cupric process distances all compeers for ease of application and delicacy of end-reaction, combined with considerable accuracy.  His solution differs from that of Fehling in containing ammonia, which dissolves the cuprous oxide as soon as it is formed, yielding a colorless solution.  It is only necessary, therefore, to note the moment that the blue color of the liquid is exactly discharged, in order to tell when all the copper present has been reduced.  Pavy’s solution is prepared as follows:  Dissolve 356 grains of Rochelle salt and the same weight of caustic potash in distilled water; dissolve separately 73 grains of recrystallized cupric sulphate in more water with heat.  Add the copper solution to that first prepared, and when cold add 12 fluid oz. of strong ammonia (sp. gr. 0.880), and distilled water to 40 fluid oz.  The estimation is thus conducted:  Dilute 10 c.c. of the ammoniated cupric solution—­equivalent to 5 milligrammes of glucose—­with 20 c.c. of distilled water, and place in a 6 or 8 oz. flask.  Attach this by means of a cork to the nozzle of an ordinary Mohr’s burette, b, preferably fitted with a glass stopcock, and filled previously with the diluted urine.  The small tube, c, which traverses the cork is intended to permit the escape of steam.  Now raise the blue liquid in the flask to active ebullition—­not too violent—­by the aid of a spirit lamp or small Bunsen flame.  Turn the stopcock in order to allow the urine to flow into the boiling solution at the rate of about 100 drops per minute (not more or much less) until the azure tint is exactly discharged.  Then stop the flow, and note the number of cubic centimeters used.  That amount of dilute urine will contain 5 milligrammes of glucose.  To render the determination as accurate as possible, the urine should be diluted to such an extent that not less than 4 or more than 7 c.c. are required to decolorize the solution, and the proportions necessary will be found to vary from 1 part of urine in 21/2 to 1 in 30 or 40.  The subsequent calculation is very simple.  If you wish to give the percentage of sugar, multiply 0.005 by 100, and divide the product by the number of cubic centimeters of dilute urine employed.  The figure thus obtained, multiplied by the extent of dilution—­i.e., if there is 1 of urine in 10, multiply by 10—­gives the required percentage.  The number of grains per fluid ounce can of course be obtained by multiplying the percentage by 4.375.  To observe easily the exact end-reaction a piece of white paper should be placed behind the flask.  If the analyst objects to the escape of the waste ammoniacal fumes, they may be conducted by a suitable arrangement into water or dilute acid.  In addition to glucose there are small quantities of other copper-reducing bodies present in all urine, which always render the reading