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COLOUK AND CHEMICAL CONSTITUTION. 
Part XIV. — The Calculation of the Colour of the Dicyclic Dyes. 
The remarkable discovery published last year in the Addendum to Part X, 
whereby I was enabled to calculate the colour of methylene-blue from that 
of a dye containing neither nitrogen nor sulphur, has in the meantime proved 
very fertile. I have now worked out all the factors whereby the colour of 
any dye made up of two ionisable rings and either one or two linkages can 
be calculated. This means calculating quite two-thirds of the known dyes. 
Dioxybenzhydrol, HO ■ C 6 H + ■ CH(OH) ■ C 6 H 4 OH is an example of a 
singly -linked dicyclic dye, and dioxy-xanthhydrol 
is an example of a doubly-linked dicyclic dye. Mono-oxybenzhydrol on the 
other hand is " monocyclic," having only one ionisable ring. 
I find if the assumption is made that the wave-length of an electron- 
orbit going round two phenol rings is about A 1380, that this orbit is 
contracted, by linkage of the rings always in the same proportion for the same 
linkage, whatever other groups are present. Each linkage thus has a colour- 
factor (less than unity) which, when multiplied by 1380, gives the colour of 
the corresponding di-oxyphenyl-dye. 
By James Moir. 
O 
Table of Linkage Factors. 
A. Methylene or 
B. Imino or 
C. Oxo- or ' / O \ 
D. Thio- or / s \ 
CH £ 
Value 0 65. 
Value 078. 
Value 0-89. 
Value 0-92. 
