Colour and Chemical ConstUntion. 
113 
which easily bleaches tlieir colour; otherwise from their brilliant colours 
they would make excellent indicators. 
Table I. 
Spectra of the Dibasic Mixed Phthaleins. 
No. 
Name. 
Colour in 
Alkali. 
i 
' Wave-lenpfth 
of Absorption 
: Band. 
Percentapfc 
J )iTierence 
from Phonol- 
phthalein. 
1 Wave-leng'th 
in cone, 
i H2SO4. 
1 
Jrnenolthymolpntnalein 
Purple 
Olo 
4'1 
About o^u 
2 
Phenolorthocresolplithalein 
Pink 
OOO 
1*5 
3 
Phenol o-uaiacolphthfilein . 
Piirple 
ooU 
4*4 
About o.::o 
4 
Phenolcarvacrolplithalein . 
ooO 
4"4 
5 
Phenol-a-iiaphtholphtha- 
Indig'o 
o 7 
ODD ana 
lein 
violet. 
a 
D 
Phenol-/3-naphtliolplitlia- 
lein 
(jrreen 
DO i 
lo 0 
7 
Plienolresorcinolphthalein 
Dicliroic- 
OOO anci 4^4 
Abnormal 
oUo 
(mixture of two) 
red 
Plienolphloroglucinolphtlia- 
Til p n T*m f* - 
550 and 490 
lein (mixture of two) 
red 
9 
Phenolpyrogallolphthaloin 
Dichroic- 
580 and 480 
(mixture of two) 
red 
10 
Phenolpyrocatecliolplitlia- 
Purple 
579 
4-3 
522 
lein 
11 
Phenolcoumarinphthalein . 
Pink 
565 (slight 
1-9 
fluorescence) 
12 
Pheiiolquinosolphthalein . 
Blue 
598 
7-3 
520 
13 
Phenolmentliolphtlialein . 
Pink 
About 563 
14 
Phenoltetrahydro-a-naph- 
l^lue- 
588 
5-8 
530 
tholphtlialein 
jnirple 
15 
Phenolanilineplithaloin 
Pink 
558 
0-7 
Ultra-violet. 
16 
Plienolmonometliylanilino- 
Ked- 
576 
3-8 
plitlialein 
purple 
17 
Phenoldimethylaniline- 
Blue- 1 
587^- 
5-6 ! 
plithaloin 
purple 1 
18 
Plienol-nr-naphthylamine- 
Yellow- 
About 740* 
25 ' 
phthalein 
green ; 
1 
(fluorescent) 
1 
* Plus ultra-violet. 
In any case the easy reaction of all these organic compounds with 
oxybenzoylbenzoic acid affords a simple analytical test for phenols and 
amines, the position of the absorption band in the spectrum at once 
indicating what the phenol (or amine) used was. 
If a numerical comparison be made between the spectra of any one 
of these m.ixed phthaleins and the corresponding ordinary phtlialein, the 
remarkable discovery is made that the mixed phthalein spectrum is not 
quite intermediate between those of phenolphthalein and the other phthalein. 
Thus di-phenolphthalein (ordinary phenolphthalein) has A 554, phenolthymol- 
phthalein has A 578, and di-thymolplithalein has A 597. In other words, 
the entrance of one pair of methyl and isopropyl groups depresses the 
