NOTES AND COMMENT 



A method for the detection of reducing sugars which is decidedly 

 more exact than the use of the customary FehHng's solution and at the 

 same time better adapted for the use of elementary students, certainly 

 deserves wide-spread adoption in botanical laboratories. The reagent 

 devised by Dr. Stanley R. Benedict, professor of chemistry at Cornell 

 Medical College, and described by him in the Journal of Biological 

 Chemistry (1909, vol. 5, p. 485 and 1911 vol. 9, p. 57) is so superior to 

 Fehling's in every way that it should entirely supercede it. Benedict's 

 reagent is made in one solution, keeps indefinitely even in half-filled 

 colorless cork-stoppered bottles, gives a more obvious reaction and is 

 ten times as sensitive as the other. 



It is prepared as follows: * 



Copper sulphate crystals 17.3 grams, dissolve in 100 cc. distilled water 

 and make up to 150 cc. 



Sodium citrate^ — -173.0 grams. 



Sodium carbonate crystals — ^200.0 grams (100.0 grams anhydrous). 



Dissolve these two together in 700 cc. of hot water and make up to 

 850 cc. 



Pour the copper sulphate solution into the other while stirring, 

 filter and the reagent is ready for use. 



To 5 cc. of this reagent add 8 or 10 drops of the solution to be tested 

 and boil vigorously for one to two minutes. If a reducing sugar be 

 present the whole mass of the fluid will become opaque because of a 

 red, yellow or brown precipitate. If the amount of sugar present be 

 minute the precipitate may not be visible until the reagent is allowed 

 to cool slowly. The bulk, not the color, of the precipitate is the basis 

 of the test. Since alkalinity in this reagent is produced by sodium 

 carbonate the test is more specific than when hydroxides of the alkali 

 metals are used, since these may exert a destructive action on carbo- 

 hydrates present before reduction. 



Benedict's reagent may be employed to give valuable demonstrations 

 of sugars in plant cells. A fresh portion of a leaf or other plant tissue 

 when boiled in the solution and then examined under the microscope, 



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