(5) 
COLOUE AND CHEMICAL CONSTITUTION: A STUDY OF THE 
PHTHALEINS AND EELATED COMPOUNDS. 
By James Moie, M.A., D.Sc, F.I.C. 
Whilst it has been known for a long time that if a coloured organic sub- 
stance or dye is converted into a substitution product (e. g. aurine into 
eupittonic acid), the colour is much deepened, yet there are remarkably few 
systematic researches on record which give any clue as to the factors govern- 
ing this phenomenon, important as it is from the practical point of view. 
Of the recorded work practically all belongs to the azo-dye series — for 
example, J. T, Hewitt's investigation into the changes of colour produced in 
nitrobenzeneazo-a-naphthol by adding the sulphonic group to its molecule 
in the different possible positions ; also the recent interesting and systematic 
work emanating from the Dacca College, India . 
The present paper purports to be, as far as possible, a complete study of 
the phthaleins and of other derivatives of the parent substance fuchsone, 
and the work has consisted, briefly, in an examination of the colour and 
absorption-spectrum of every phthalein and oxy- derivative of triphenylcar- 
binol that could be made with the materials at my disposal, and of an 
attempt to include all the numerous and puzzling data in a comprehensive 
theory of colour-change. 
The simplest phthalein possible is monoxydiphenylphthalide (also known 
as phenylphenolphthalein, and in Oermany incorrectly as " benzolphenol- 
phthalein"), a colourless substance usually depicted by the formula 
> 
\ 
>C— / NoH 
/ \/ o — 
which, when dissolved in alkali, becomes coloured (a rather purplish pink), 
and is then assumed to have been converted into the quinonoid form : 
■ \ / 
\ / 
COONa 
