234 
Transactions of the Royal Society of South Africa. 
7. C-phenyl-derivative of foregoing, from benzoylbenzoic acid and 
a-naphthol, has A 401 in alkali. In strong sulphuric acid, however, it has 
the much higher colour A 543. 
8. l-4'-dioxybenznaphthydrol, from _p-oxybenzaldehyd and a-naphthol, 
is violet with A 590 in alkali. I have assumed the constitution to be 
OH 
ho/ 
on the analogy of naphtholphthalein (Berichte, 1920, 1445). 
9. The corresponding substance from /3-naphthol, 
<::> 
HO— <^ CHOH— <^ N , 
OH 
or 2-4'-dioxybenznaphthydrol, has A 556, with a pink colour. 
10. Phenol-/3-naphtholphthalein, the benzoic acid-derivative of the 
foregoing, 
OH_ 
HO—/ ^_COH— <^ ^> 
I <::>- 
C 6 H 4 C0 2 H 
is now found to have A 570 (broad). My statement in Part II (1918, p. 113), 
that it has A 637, is erroneous. 
The naphthol/phenol colour-factor from these two substances is quite 
different from that obtained when the C 4 H 4 group of the naphthalene-ring 
is joined metapara to the benzhydrol linkage, viz. 1-026 for orthometa- as 
against 1-082 for metopara-attachment. 
From these data I can roughly predict the wave-length of the still 
unknown j9-j9-a-naphtholphthalein to be about A 628, that of the commercial 
o-o-a-naphtholphthalein being A 662.* 
B. Further Derivatives of Phenolphthalein (Part IN— continued). 
(a) 3- (or 6)-oxyphenolphthalein, from 3-oxyphthalic acid, has A 556 
in NaOH and is higher in bicarbonate (A 562). 
* When, however, the hydroxyl is para to the benzhydrol linkage, a third 
naphthol/phenol factor comes into play. Its value is 1-042 (see Part XV, Naphtho- 
fluorescein). The true calculated A of p-p-a -naphtholphthalein is 602. This is also 
the factor for safranines like Magdala-red. 
