Dichromatism of bromphenol blue, with an improvement in the mercuric bromphenol blue technic for protein.

Staining of protein in sections using the mercuric bromphenol blue technic is improved by staining with 1% HgCl2 and 0.05% bromphenol blue in 2% aqueous acetic acid for 15 min at room temperature. Rinse slides 20 min in 2 changes of 0.5% aqueous acetic acid. Blot and give 2 fast changes in absolute ethanol with agitation before transferring to xylene. Transfer slide to 0.5% n-butylamine in xylene for a few seconds until the section is blue, then, after 2 changes of xylene, mount in DPX. Spectrophotometric analysis of this blue dye at different concentrations and with or without heparin showed that the reddish hues are due to dichromatism and not metachromasia.