A somewhat simpler application of this method, which is accurate enough for clinical purposes, is as follows: Take 8¾ c.c. (roughly, 9 c.c.) of Purdy's solution in a large test-tube, dilute with an equal volume of water, heat to boiling, and, while keeping the solution hot but not boiling, add the urine drop by drop from a medicine-dropper until the blue color is entirely gone. Toward the end add the drops very slowly, not more than 4 or 5 a minute. Divide 10 by the number of drops required to discharge the blue color; the quotient will be the percentage of glucose. If 20 drops were required, the percentage would be 10÷20 = 0.5 per cent. It is imperative that the drops be of such size that 20 of them will make 1 c.c. Test the dropper with urine, not water. If the drops are too large, draw out the tip of the dropper; if too small, file off the tip. _Purdy's solution_ consists of pure crystalline copper sulphate, 4.752 gm.; potassium hydroxid, 23.5 gm.; ammonia (U.S.P.; sp. gr., 0.9), 350 c.c.; glycerin, 38 c.c.; distilled water, to make {81} 1000 c.c. Dissolve the copper sulphate and glycerin in 200 c.c. of the water by aid of gentle heat. In another 200 c.c. of water dissolve the potassium hydroxid. Mix the two solutions, and when cool, add the ammonia. Lastly, bring the whole up to 1000 c.c. with distilled water. This solution is of such strength that the copper in 35 c.c. will be reduced by exactly 0.02 gm. of glucose. (2) Fehling's Method.--Take 10 c.c. Fehling's solution (made by mixing 5 c.c. each of the copper and alkaline solutions described on page 78) in a flask or beaker, add three or four volumes of water, boil, and add the urine very slowly from a buret until the solution is completely decolorized, heating but not boiling after each addition. Fehling's solution is of such strength that the copper in 10 c.c. will be reduced by exactly 0.05 gm. of glucose. Therefore, the amount of urine required to decolorize the test solution contains just 0.05 gm. glucose, and the percentage is easily calculated. [Illustration: FIG. 25.--Einhorn's saccharimeter.] (3) Fermentation Method.--This is convenient and satisfactory, its chief disadvantage being the time required. It {82} depends upon the fact that glucose is fermented by yeast with evolution of CO_{2}. The amount of gas evolved is an index of the amount of glucose. Einhorn's saccharimeter (Fig. 25) is the simplest apparatus.