Instead of resorcin one can also use 1-naphthol (see literature).
The diluted residue can be discharged into the drainage.
Due to the seperation of water fructose 5 -(hydroxymethyl)furfural is formed. This reacts with resorcin along with a renewed seperation of water to form the colorant shown below, as well as isomers of this. The formation of furfural derivates, upon which this verification is based, succeeds under these conditions only with certain ketoses.
Verification of fructose
Derived from p. 203, 
Concerning the use of 1-naphthol as a detection agent: to be added,