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COLOUR AND CHEMICAL CONSTITUTION. 
Part X. — A General Numerical Solution of the Colour- 
Constitution Problem. 
By James Moir. 
In Part IX of this work it was shown that the spectra and colours of a 
particular class of triphenylcarbinol colours (viz. halogenated phthaleins) 
■could be calculated from the data of a parent-substance by multiplying 
by a factor dependent on the nature, number and position of the substituents. 
I have now discovered that this principle can be applied to all the 
ordinary triphenylcarbinol dyes ("aniline dyes'), the colours of which 
can now be calculated, as will be seen below. 
It has been shown in earlier parts of this work that the colour-phenomenon 
is additive, i. e. that each group present acts in colour-change almost in- 
dependently of other groups and of the rest of the molecule. 
I now find that each combination of group and position, e. g., orthomethyl, 
parahydroxyl, etc., can be assigned a colour-factor by means of which the 
effect on colour of the substitution of the group for hydrogen in the given 
position can be calculated : even if five or six groups are present it is found 
that by multiplying the wave-length of the parent substance by all the 
factors of the groups present in a coloured substance a result is obtained 
which tallies closely with observation. 
The apparent inconsistency between the new factorial notion and the 
additive " notion is merely accidental. It is a well-known fact in mathe- 
matics that (1 + rt ) (1 — h) = 1 a — b without serious error unless a or l> is 
more than or so. The " factors " are of the form 1 + a or 1 — b and the 
additive notion corresponds to the right side of the equation. 
The parent-substance taken is an imaginary one,* Ijeing the anhydride of 
triphenylcarbinol or ^j-phenylenediphenylmethane : 
* Said, however, to have been made; see Beilsteiii, ii, p. 292. 
