Colour and Chemical Constitution. 
185 
giving a second theoretical value for the band-centre in the supposed 
unknown thymolnaphtholphthalein, viz. 607 x 1*044 or X 634. 
The observed value being X 633, it is seen that both predictions are 
accurate. 
(9) Thy7nol-a-anthrolphthalei7i, from thymoylbenzoic acid and a-anthrol, 
is bluish-olive in alkali with an indefinite spectrum consisting of a strong 
dulling of the yellowish-green and the outer red. The centre of the latter 
band is probably X 710, and the other may be due to the presence of a little 
thymolphthalein. In H^SOj the colour is emerald and the absorption-band 
sharp with centre at X 636. 
(10) Monojplienyl ether of jjhenolphtJialein. — An attempt to make this 
substance from oxybenzoylbenzoic acid and (Cp,H-)oO using HoSO^ as 
condensing agent gave a product which was mostly composed of phenol- 
phthalein, but also contained another substance having a broad band with 
centre at X 470. It is c[uite probable that the latter substance is merely 
/?-oxyanthraquinone (see Part III), the absorption-band of which was 
observed to be at X 475 (a-oxyanthraquinone has its band-centre at X 490). 
Secondary hands of the phthaleins. — The existence of an absorption-band 
possessing f of the wave-length and f of the frequency of the visible band 
having been suspected (and indicated in Part I), an examination of the 
extreme violet end was attempted. Lack of quartz apparatus prevented 
the application of the photographic method. It was found that strong 
solution of alkaline phenolphthalein absorbs the extreme violet, the edge of 
the band coming up to X 380, which is consistent with the presence of a 
band with its centre at f x 554 or X 369. In the case of thymolphthalein 
in strong solution in alkali the absorption of the violet is almost total, the 
edge of the absorption extending to X 420 (| x 597 = X 398 calculated for 
centre). 
B. Derivatives of o-j^-phenolphthalein. 
{a) Fhenolquinolphthalein. — This is obtained as usual from oxybenzoyl- 
benzoic acid and quinol, but purification of the product was unsuccessful, 
and since the al)sorption-band is vague, no further investigation was made. 
The colour of the phthalein in alkali is maroon : band-centre about X 540? 
i.e. lower than that of any of the para-phthaleins. In HoSO^ the phthalein 
gives a yellow solution, the band being extremely far down in the blue, 
at about X 435 — a position similar to that of fluoresceine in H.^SO^j. 
(6) Ethyl ether of foregoing phthalein. — This was obtained by using 
EtO<^ ^OH (from pheiietidine) instead of quinol. The product was 
also unsatisfactory. The alkaline colour is dirty purple with a very broad 
band at about X 552 and signs of another at about X 490. 
(c) Thymol-'p-ethoxyjjhenol-phthalein from EtO 
OH and thymoyl- 
