Abstract: In this paper, the visible absorption spectra of the reineckates of hetrazan and piperazine citrate in acetone were studied and found to be similar to that of the reagent itself rather than of the organic bases. The molecular composition of the reineckates has been confirmed by molecular weight determination. Furthermore, the solubility (in water) and the gram-molecular extinction coefficient of the reineckates were also determined. Based on these experiments and the red colour of the reineckates in acetone, a colorimetric method for the estimation of hetrazan, piperazine citrate, and most of their preparations is proposed. In comparsion with the solvent extration or gravimetric procedure, it is simple, rapid, and accurate, which is therefore quite suitable as a routine method for quality control purpose.