Colour and Chemical Constitution. 
131 
assume to be the f or g derivative, not the j or Jc derivative : the same holds 
of the positions e, h, i and I, there being only one mono-metabromphenol- 
phthalein. On inspection of the figure it will be seen that only five distinct 
monobromphenolphthaleins are to be expected, or at all events, although six 
are possible {a, h, c, d, e and /), yet the a and the d derivatives either have 
the same spectrum or are never formed together when 3-bromophthalic acid 
is condensed with phenol (this might be expected owing to " protection," 
which would prevent the formation of the d derivative). 
Mo7iohromop7ie7iolp]ithaleins. 
Position of bromine 
atom. 
Method of formation. 
Observed 
band- centre. 
Calculated from 
position-law. 
a 
3-bromophthalic acid and phenol 
X 566 
X 564 
h 
Bye-prodvict of c 
X 556* 
X 555 
c 
4-broniophtlialic acid and plienol 
X561* 
X 562 
e 
OBBAf and monometabromphenol 
X567 
X 569 
f 
OBBAf and mono-orthobromphenol 
X561^ 
X 562 
* Imperfectly separated. f OBBA = 4j-oxybenzoylbenzoic acid. 
For comparison with the first of these, a-monochlorphenolplithalein 
was made. Its band-centre was at x 563. 
As regards the dibromophenolphthaleins, there appear to be 21 possible 
isomers, viz.: (1) a-d from 3-6-dibromphthalic acid; (2) h-c from 4-5- 
dibromphthalic acid ; (3) a-b and (4) c-d from 3-4-dibromphthalic acid ; 
(5) a-c and (6) h~d from 3-5-dibromphthalic acid ; (7) a~e and (8) d~e from 
3-(6)-bromo-4'-oxybenzophenone-2-carboxylic acid and metabromphenol ; 
(9) h-e and (10) c-e from the isomeric 4-(5)-bromo acid ; (11) a-f and (12) 
d-f horn the former acid and orthobromphenol ; (13) 6-/ and (14) c-/from 
the isomeric 4-bromo-4'-oxybenzophenone-2-carboxylic acid and orthobrom- 
phenol ; (15) e-f from OBBAf and 2-3-dibromphenol ; (16) e-g similarly 
from 2-5-dibromphenol ; (17) e-h similarly from 3-5-dibromphenol ; (18)/-^ 
similarly from 2-6-dibromphenol ; (19) e-i from phthalic acid and 2 mols. 
metabromphenol ; (20) f-j from phthalic acid and 2 mols. orthobromphenol ; 
and finally (21) e-j by condensing phthalic acid first with orthobromphenol 
and then with metabromphenol. 
Of these 21 isomers, 4 may be eliminated if we assume that the colour- 
effect of the cZ-position is the same as that of the a-position ; these 4 are 
h-d, c-d, d-e and d-f. Of the 17 remaining I have, of course, only been 
able to prepare and examine a very few, owing to lack of starting-substances 
in South Africa, and the following table exhibits the results obtained : 
