41 8 PHYSIOLOGICAL CHEMISTRY 



oxide instead of being a precipitate of cuprous hydroxide or oxide as is the case 

 when the original Fehling solution is reduced. 



Benedict claims that, whereas the original Fehling's test will not 

 serve to detect sugar when present in a concentration of less than o.i 

 per cent, that the above modification will serve to detect sugar when 

 present in as small quantity as 0.015-0.02 per cent. This claim has 

 been corroborated by Harrison. 1 The modified solution used in the 

 above test differs from the original in that 100 grams of sodium car- 

 bonate is substituted for the 125 grams of potassium hydroxide ordi- 

 narily used, thus forming a Fehling solution which is considerably 

 less alkaline than the original. This alteration in the composition of 

 the Fehling solution is of advantage in the detection of sugar in the 

 urine inasmuch as the strong alkalinity of the ordinary Fehling solu- 

 tion has a tendency, when the reagent is boiled with a urine containing 

 a small amount of glucose, to decompose sufficient of the sugar to 

 render the detection of the remaining portion exceedingly difficult 

 by the usual technic. Benedict claims that for this reason the use of 

 his modified solution permits the detection of smaller amounts of sugar 

 than does the use of the ordinary Fehling solution. 



Second Modification. 2 Benedict has further modified his solution and has 

 succeeded in obtaining one which does not deteriorate upon long standing. 3 

 The following is the procedure for the detection of glucose in the urine : To 5 c.c. 

 of the reagent in a test-tube add 8 (not more) drops of the urine to be examined. 

 The fluid is then boiled vigorously for from one to two minutes and then allowed 

 to cool spontaneously. In the presence of glucose the entire body of the solution 

 will be filled with a precipitate, which may be red, yellow, or green in color, de- 

 pending upon the amount of sugar present. If no glucose is present, the solution 

 will either remain perfectly clear, or will show a very faint turbidity, due to 

 precipitated urates. 



Even very small quantities ot glucose in urine (o.i per cent) 

 yield precipitates of surprising bulk with this reagent, and the positive 

 reaction for glucose is the filling of the entire body of the solution 

 with a precipitate, so that the solution becomes opaque. Since amount 



1 Harrison: Pharm. Jour., 87, 746, 1911. 



2 Benedict: Jour. Am.Med. Ass'n, 57, 1193, 1911. 



3 Benedict's new solution has the following composition: 



Copper sulphate 17.3 gm. 



Sodium citrate 173.0 gm. 



Sodium carbonate (anhydrous) 100. o gm. 



Distilled water to 1000.0 c.c. 



With the aid of heat dissolve the sodium citrate and carbonate in about 600 c.c. of water. 

 Pour (through a folded filter if necessary) into a glass graduate and make up to 850 c.c. 

 Dissolve the copper sulphate in about 100 c.c. of water and make up to 150 c.c. Pour the 

 carbonate-citrate solution into a large beaker or casserole and add the copper sulphate 

 solution slowly, with constant stirring. The mixed solution is ready for use, and does not 

 deteriorate upon long standing. 



