Abstract
1. The chromatographic behaviour of 22 closely related N-alkyl thionins in a number of solvent systems is described.
2. Details are given of the separation of commercial mixtures of the azures into their components and the application of this to the analysis of Romanowsky stains.
3. A table giving the Rf equivalents and absorption maxima of the dyes is appended and the additive effect of alkyl substitution is discussed.