Quarterly Journal of Microscopical Science, Vol s3-101, 255-272, Copyright © 1960 by Company of Biologists

Experiments on the Action of Mordants

I. ‘Single-Bath’ Mordant Dyeing

¹ Cytological Laboratory, Department of Zoology, University Museum, Oxford

Aluminium sulphate was chosen as the simplest mordant, and purpurine (1,2,4-hydroxyanthraquinone) as the simplest dye suitable for use in experiments with mordants.

It was shown by a series of experiments that a solution containing about 16 atoms of aluminium to each molecule of purpurine has special properties. A section already dyed with an aluminium/purpurine solution till chromatin is dark and cytoplasm lightly tinged, is in equilibrium with such a solution: that is to say, it neither takes up more dye nor loses any part of what it already holds. If the proportion of dye to mordant is increased, the section will take up more of the dye; if the proportion of the mordant to the dye is increased, the section will lose part or all of the dye it held.

The experiments described in the paper, taken in conjunction with existing knowledge of the behaviour of aluminion ions in solution and of their capacity to form chelate compounds with anthraquinonoid dyes, afford a basis for the following theory of single-bath mordant dyeing by aluminium/purpurine.

One purpurine ion chelates with one hydrated aluminium ion to form a complex ion with double positive charge; this is attracted to sites of negative charge in the tissues, such as the phosphoric groups of the nucleic acids. Electrostatic attraction is replaced by covalent bonds, resistant to solution by neutral ethanol. In extraction (‘differentiation’) by the mordant, the dye partitions itself between the tissue/mordant complex on one hand and the dissolved mordant on the other.