Chromatic Theory Research Articles

Some observations on screened indicators for the direct chelatometric titration of calcium

The screening of five common metallochromic indicators used in the complexometric determination of Ca was studied using tristimulus chromaticity theory. Calcon-tartrazine-Orange II (6.8 + 1 + 4.6, w w ), thymolphthalein complexone-Orange II-tartrazine (14.22 + 1.22 + 1), Arsenazo III-Remazol Brilliant Blue-tartrazine (25.2 + 8.9 + 1), phthalein complexone-tartrazine-Remazol Brilliant Blue (2.47 + 1 + 1.1), and methylthymol Blue-Orange II-tartrazine (13 + 2.9 + 1) are proposed for the titration of calcium against Na 2 EDTA. The clarity and accuracy of titration are improved.

Performance comparison of five metallochromic indicators for barium

The color transitions produced by certain metallochromic indicators used in the complexometric determination of Ba (with EDTA) were studied using tristimulus chromaticity theory. Metalphthalein, thymolphthalein complexone, methylthymol blue, antipyryl- o-arsenazo I, and antipyryl- p-arsenazo I were the indicators studied. The results obtained indicate that, of the indicators considered here, the most suitable for visual titration of Ba with EDTA are metalphthalein and thymolphthalein complexone.

The dichromatic number of a digraph

In this paper the concept of dichromatic number of a digraph which is a generalization of the chromatic number of a graph is introduced. The dichromatic number of a digraph D is defined as the minimum number of colours required to colour the vertices of D in such a way that the chromatic classes induce acyclic subdigraphs in D. Some results relating the dichromatic number of D with the existence of cycles of special lengths in D are presented. Contributions to chromatic theory are also obtained. In particular, we generalize the theorem due to P. Erdös and A. Hajnal ( Acta Math. Acad. Sci. Hungar. 17 (1966), 61–99) which states the existence of odd cycles of length ≥ χ ( G) − 1 in any graph G.