126 
Transactions of the Royal Society of South Africa. 
p-iodophenol and p-oxybenzoylbenzoic acid) an attempt was made by 
reduction to obtain the unknown parent substance o-^-phenolplithalein 
itself. The product of the condensation was for this purpose digested with 
a large excess of zinc dust, both acid and alkaline media being tried, and 
then reoxidised from phthalme to phthale^?^ with HoOo, but I did not 
succeed in obtaining a product completely free from iodine ; and, most 
remarkable to say, the product resembled ordinary phenolphthalein very 
closely. 
Its alkaline absorption-band is at \ 558 and its H0SO4 band is at X 503, 
the figures for ordinary phenolphthalein being 554 and 499 respectively. 
The absorption-band is broader in the supposed o-p. compound and the 
colour is comparatively easily bleached by excess of alkali, whereas ordinary 
phenolphthalein requires strong alkali to bleach it. Further work on this 
point liad to be abandoned on account of the complication introduced by the 
discovery which I next made, namely that^-oxybenzoylbenzoic acid yields a 
plithalein-like substance when heated alone to over 200° C. or at a lower 
temperature when heated with a little sulphuric acid. The former observa- 
tion has already been made by Orndorff and Murray ('J. Amer. Chem. Soc.,' 
April, 1917, p. 681) in the course of their preparation of another (nearly 
colourless) anhydride of oxybenzoylbenzoic acid, but these authors, misled 
by an approximation in colour, state that the second substance is phenol- 
phthalein. 
The substance can also be obtained by heating " phenolplithaleinoxime " 
with a small quantity of H^SO^ to over 200° C. until a trace withdrawn and 
dissolved in cone. HoSO^, no longer shows a spectrum absorption at X 459 
but only the band at about X 500 due to the new substance. Excess of 
H0SO4 must not be used in this preparation, else another substance, which 
appears to be /3-oxyanthraquinone, is produced, which has a very broad 
absorption-band across F when dissolved in alkali. 
It is probable that " phenolphthalein- oxime " is not an oxime at all, but 
is the j)-oxyanilide of ^-oxybenzoylbenzoic acid, its formation being as 
follows : 
COOH 
+ H • NHOH = H0< 
NHOH ^^2^ 
Plienolphthalein. 
Hydroxylamine. 
" Phenolphthaleinoxime." 
