(Ill) 
COLOUR AND CHEMICAL CONSTITUTION. 
Part IL — The Spectra of the Mixed Phthaleins and of the 
sulphone-phthaleins. 
By James Moir, M.A., D.Sc, F.I.C. 
In the first part of this paper (read March 21, 1917; sent in January 
18th) an attempt was made to discover the laws which govern the colour 
of organic dye-stuffs by choosing one of such simple constitution and easy 
manufacture that it was not a troublesome matter to prepare and examine 
a large number (over fifty) of derivatives of the parent substance, and thus 
solve, to a large extent, the problem of the effect on colour of varying the 
substituting groups — without wasting a lifetime in the preparation of the 
necessary compounds. 
Phenolphthalein is a quasi-symmetrical compound, since it contains 
two equal — CgH^OH groups, and the same is true of about forty of the 
compounds described in Part I ; but in addition a number of compounds 
were described which have - G^H- plus — CgH^OH, and are thus mixed 
phthaleins of a kind, althougli not dibasic like the true phthaleins. They 
were made by condensing benzoylbenzoic acid with phenols. 
In April of this year (1917) it struck me that substituted benzoyl-benzoic 
acids, particularly 
^<Z><Z> 
C02H 
(which is easily made from phenolphthaleinoxime), might be used to make 
true dibasic mixed phthaleins containing one - CgHj^OH group as well as 
the residue of another phenol - CgHj_„X„OH. 
On trying the experiments I found that the above-mentioned |?-oxy- 
benzoyl-o-benzoic acid is capable of combining with all sorts of phenols 
with the utmost ease ; in most cases simple boiling of a mixture of the 
ingredients without a condensing agent for ten seconds suffices to give a 
good yield of the desired mixed phthalein. In addition, the acid can 
combine with the most unexpected aromatic substances (phenol-esters, 
anhydrides, and amines, whether free or substituted in the nitrogeinl^ to 
9 
