Colour and Chemical Constitution. 
37 
Armed with these data we proceed to calculate the colours of the known 
monocyclic coloured substances, and to predict the colours of the unknown 
or unobserved members of the series. 
(1) Fuchsone — This is the diphenyl derivative of the parent- substance. 
Its calculated X is therefore 290A' 2 = 290 x 1 135 x 1 135 = X 374. Meyer 
and Fischer observed \380 in alcohol ('Berichte,' 1913, p. 70). Observations 
in alcohol generally give results about 6 units higher than in water. 
(2) Paraoxybenzhydrol. — This is the mono-phenyl derivative, and its 
calculated X is 329. It has not been observed, but this value is predicted 
for its colour in alkali. Ortho-oxybenzhydrol is known, and is yellow 
with X about 360 (' Beilstein,' ii supplement, p. 694). This is about the 
usual difference in colour between ortho- and para-compounds, so that the 
prediction is probably correct. 
(3) Fuchsimine (fuchsone-imine) .— This is fuchsone with NIL in place 
of OH. The calculated X is — 
f 290 x 1T35 2 x factor D) 
1 = X 426|. 
lor 374 x 1 14 ) 
Observations by Meyer and Fischer {I. c.) gave x 430 in alcohol. My own 
observation, in water, gives X 425. 
(4) Fuchsonedimethylimonium salts. — The calculated value is that of 
fuchsone multiplied by the factor Gr, viz. 374 x 1 22 = X456. Meyer and 
Fischer give X 460 in alcohol. My observation in water is X 455. 
(5) Mono-oxydiphenylphthalide (phenylphenoljjJithalein). — This is the 
ortho-carboxylic acid of fuchsone. Its calculated colour corresponds 
to \ 374 x 1-060 = \ 397. My observation gives X 395 in water. 
In Parts I and III of this work I stated that I had observed a pink 
(instead of a yellow) colour in this substance (X560). This work I now 
find to be erroneous, for if oxydiphenylphthalide is made from a specimen 
of benzoylbenzoic acid which has been purified by frequent crystallisation of 
its ammonium salt (whereby ammonium phthalate is completely eliminated), 
the product gives a pure yellow in alkali without a trace of the band near 
560. The similar compound from salicylic acid (second diagram on p. 125 
of Part III) is also wrong : X 562 should be X 420. 
(6) Phenyl-dimethylaniline phthalein. — As will be seen by writing out 
its formula, this is the ortho-carboxylic acid of No. 4 mentioned above. 
Its calculated colour is therefore that of No. 4 multiplied by 1*06 = X 483. 
The substance is made from benzoylbenzoic acid and dimethylaniline, and my 
observation of its colour gives X 480 for the centre of its absorption band. 
The unknown phenylanilinephthalein should have X 452. 
(7) Para-dimethylaminobenzhydrol. — This is most simply calculated by 
multiplying the colour-figure for oxybenzhydrol (No. 2) by factor Gr. The 
calculated X is 329 x 1 22 = X 401. Observation in a specimen from 
benzaldehyd and dimethylaniline gave X 400. 
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