When ordinary laboratory Schiff's reagent is
mixed with solutions of certain aromatic aldehydes
a yellow precipitate is formed instead or the usual
The reaction of almost 50 aldehydes to Schiff's
reagent is given and this abnormal precipitation is
shown to tare place only with aromatic ortho-hydroxy
aldehydes with two exceptions in the cases of cinnan-aldehyde and ìndole aldehyde.
Excess of SO₂ favours the normal reaction
and inhibits the precipitation or the yellow compounds
The precipitates are amorphous insoluble
mixtures and are hydrated Schiff's bases which are
produced by the condensation of the pararosaniline-c-leueosulphonic acid of the Schiff's reagent with the
aldehyde. A theory is put forward to explain the
abnormal reaction. The colouration of Schiff's reagent which results when the reagent is heated has been
examined in detail and an explanation put forward.