310 Tmnsactio7is of the Boyal Society of South Africa. 
580, 607, 632. It is unfortunate that the series is incomplete ; but on the 
existing evidence it seems that the change of colour takes one regular 
path in neutral solution, and another, equally regular but different, in acid 
solution. This amounts to the assumption that there are separate colour- 
factors for the ionised — NH.j"^ and — NHMeo"^ groups different from the 
factors for — NH3 and — NMeo, and there the matter may rest until the 
lacunae in the evidence are filled. 
There are other lacunae in a complete colour-scheme for triphenyl- 
carbinol-derivatives, namely, colour-factors for groups and positions which 
occur only once. In a special investigation of benzaurine-derivatives I 
have endeavoured to find approximations to the values of most of the 
remaining colour-factors, and the results are given below : 
Name of substance. 
Source. 
A. 
Name of colour- 
Valvie of 
factor. 
factor. 
1 
a-bromobenzatirine 
Orthobrombenzoic 
acid and phenol 
568 
rt-bromo 
1-027 
2 
/3-bromobenzaurine 
Metabrombenzoic 
565 
/3-bromo 
1-022 
acid and phenol 
3 
y-bromobenzaurine 
Parabrombenzoic 
539 
y-bromo 
0-975 
acid and phenol 
4 
Phenolisophthalein 
Isophthalic acid and 
phenol 
560 
|3-carboxyl 
1-012 
5 
Phenolterephthalein . 
Terephthalic acid 
and phenol 
550 
y-carboxyl 
0-995 
6 
Metasulphobenzaurine 
Metasulphobenzoic 
560 
/3- sulphonyl 
1-01 
acid and phenol 
(vague) 
7 
Parasulphobenzaurine 
ParasnljDhobenzoic 
acid and phenol 
568 
y-sulphonyl 
1-027* 
8 
£-sulphobenzaurine 
Sulphonation of 
559 
£-sulphonyl 
1-010 
benzaurine 
9 
a-aminobenzaurine 
Anthranilic acid 
and i^henol 
565 
0 -amino 
1-022 
10 
Michler's hydrol 
cf. Malachite -green 
619 : 603 
C-phenyl 
l-026t 
* Abnormal : less than unity expected, 
t Hereby the diphenylcarbinol dyes can be calculated from f uchsene. 
The 8-position in benzaurine appears to be difiicult to investigate, or is 
possibly quite abnormal. The only substance bearing on it which I have 
succeeded in making is in the aurine series, and is the S-methyl-derivative 
of oxymalachite green (from Michler's ketone and metacresol). This has 
X 587 when basic and \617 when faintly acid. Malachite- green having \ 619, 
we see that the combination of y-OH and a-CHg is almost self-extinguish- 
ing, the factor being 0*997, so that (in the aurine series) a-CH.^ (=6-CH3) 
is about 1-030, whereas from the metacresolphthaleins the value is about 
1-026. 
In conclusion, I wish to point out an extension of this colour-theory to 
dyes outside the triphenyl-carbinol series, e. g. the ratio of the wave-lengths 
of methylene-blue and thionine, 665-^602, is the same as that of malachite- 
