42 
Transactions of the Royal Society of South Africa. 
easily goes colourless through hydrolysis to ordinary phenolphthalein and 
possesses a broad absorption band, with its centre about a 523. The 
behaviour towards alkali differs in two respects from that of phenol- 
phthalein : (1) It is coloured by bicarbonates, phenolphthalein remaining 
colourless ; the colour is violet-pink with band-centre at x 560 (phenol- 
phthalein A 554) : (2) the colour is not bleached and the substance is not 
easily hydrolysed by strong alkali ; the shade becomes rather more violet 
and the band centre moves to x 567 (cf similar behaviour of benzaurine). 
Altogether, therefore, the three yellow substances very closely resemble 
benzaurine, and, in fact, their spectra are the same as thatjof benzaurine with 
the band slightly moved towards the red by " loading " with the respective 
substituent groups (viz. para — SO3H, ortho — SO.^H, andortho — CO.OCH3 
respectively) — a phenomenon already discussed in Part I in connection with 
the derivatives of ordinary phenolphthalein. It follows, therefore, that the 
yellow colour is the normal phenomenon, since it occurs in the parent sub- 
stance benzaurine itself, and is due to the quinonoid linkage in benzaurine 
when formulated as mono-para-oxyfuchsone (phenylphenol methylene- 
quinone). The colourlessness of phenolphthalein is abnormal in this sense, 
being due to a tendency to ring-formation with the central carbon-atom 
thus : 
<z>--<z>- — <z>-f<z>- 
Theoretical benzaurine-carboxylic acid Phenolphthalein 
(should be yellow). (colourless). 
Part YI. — The Ultra-violet Spectra of the Phthaleins. 
At the end of Part I, read in March, 1917, I indicated that I suspected 
the phthalein bands seen in H2SO4 solution to be due to the " loading " with 
HoSO^ of bands in the ultra-violet, which thus were brought into the visible 
spectrum, and in Parts III and IV, I showed that by using a strong solution 
of alkaline phenolphthalein its suspected ultra-violet band could be so 
broadened that a portion of it became visible between A 360 and A 400 ; also 
that in the case of otherwise loaded phthaleins, like thymolphthalein, the 
low- violet bands are easily visible generally round about A 400. 
It gives me, therefore, great pleasure to announce that my observations 
have been confirmed and extended by photographic means in America. 
Hitherto I have only had access to an abstract of the new work (H. E. 
Howe and K. S. Gribson, .of Cornell University,'Physical Eeview,' 1917, p. 767), 
but two new ultra-violet bands of alkaline phenolphthalein are described, 
lying at aa 370 and 277, and, in addition, the American authors' measure- 
