CARBOHYDRATES. 2Q 



The modified Fehling solution used in the above test differs from 

 the original Fehling solution in that 100 grams of sodium car- 

 bonate is substituted for the 125 grams of potassium hydroxide 

 ordinarily used, thus forming a Fehling solution which is consid- 

 erably less alkaline than the original. This alteration in the com- 

 position of the Fehling solution is of advantage in the detection 

 of sugar in the urine inasmuch as the strong alkalinity of the 

 ordinary Fehling solution has a tendency, when the reagent is 

 boiled with a urine containing a small amount of dextrose, to 

 decompose sufficient of the sugar to render the detection of the 

 remaining portion exceedingly difficult by the usual technique. 

 Benedict claims that for this reason the use of his modified solu- 

 tion permits the detection of much smaller amounts of sugar than 

 does the use of the ordinary Fehling solution. He has further 

 modified his solution for use in the quantitative determination 

 of sugar (see Chapter XXII). 



Second Modification. 1 Very recently Benedict has further modi- 

 fied his solution and has succeeded in obtaining one which does not 

 deteriorate upon long standing. 2 The following is the procedure 

 for the detection of dextrose in solution : To five cubic centimeters 

 of the reagent in a test-tube add eight (not more) drops of the 

 solution under examination. Boil the mixture vigorously for from 

 one to two minutes and then allow the fluid to cool spontaneously. 

 In the, presence of dextrose the entire body of the solution will be 

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

 depending upon the amount of sugar present. If no dextrose is 

 present, the solution will remain perfectly clear. (If urine is being 

 tested, it may show a very faint turbidity, due to precipitated 

 urates.) Even very small quantities of dextrose (o.i per cent) 



1 Private communication from Dr. S. R. Benedict. *i 



2 Benedict's new solution has the following composition : 



Cupric sulphate 17.3 grams. 



Sodium citrate I73-O grams. 



Sodium carbonate (anhydrous) 100.0 grams. 



Distilled water to make I liter. 



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

 of water. Pour (through a folded filter paper if necessary) into a glass gradu- 

 ate and make up to 850 c.c. Dissolve the cupric 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 cupric sulphate solution slowly, with constant 

 stirring. The mixed solution is ready for use and does not deteriorate upon 

 long standing. 



