A reagent for the detection of reducing sugars. 1908.

It has already been shown that the hydroxides of the alkali metals have a greater destructive action upon dextrose and various other carbohydrates than have the carbonates,’ and in accordance with this fact, a copper-containing solution in which the alkalinity is secured by sodium carbonate makes a more delicate and specific test for the detection of dextrose than does a copper solution which contains sodium hydroxide. A reagent of this nature, containing copper sulphate, Rochelle salt, and sodium carbonate, was suggested in a previous paper.2 This reagent affords a delicate test solution for dextrose, but it has the disadvantage common to so many of the alkaline copper solutions, viz: that after mixing, it rapidly deteriorates and soon becomes useless for detecting small quantities of sugar. For this reason it seemed desirable to obtain a solution in which the alkalinity is secured by carbonate, and which shall at the same time be permanent after mixing. Rochelle salt is the constituent of the alkaline copper solutions which undergoes change upon standing, and forms products which cause a spontaneous reduction of the solution. As a substitute for the tartrate we may (theoretically) use any aliphatic compound which carries two or more OH radicals, and which is in itself incapable of reducing the copper at a boiling temperature. Substances in great number and variety have been proposed in the literature as substitutes for the Rochelle salt in Fehling’s solution. In the present case, where the alkalinity is to be secured by carbonate, it was found that none of the substances usually employed could be used with advantage. Thus glycerol and mannite almost always carry sufficient reducing substance as