70 
Transactions of the Royal Society of South Africa. 
Calculated A = 1400 x 078x0-47 x 1-026 (for phenyl) x (1-012) 2 (= benzo- 
flavine x 0-47 -r- 0-39) = A 541. Observations in commercial specimens vary 
between A 530 and A 540 ; probably some do not contain the methyl groups. 
(31) Methylene violet. — This is isomeric with safranine, but the two 
methyls are on nitrogen not in the ring. Calculated 1473 (see No. 29) X 
0 39 x 0'78 x T026 = A 554. Commercial specimens vary in observation 
between A 550 and A 565, being mixtures. Another way of calculating this 
isomeric substance is to note that the N-methyl group has twice the effect 
of the C-methyl group, the latter having a factor of 1012 ; the former has 
a factor of (1-012)2 = 1-0245 (see Part X, p. 305). Consequently No. 31 
calculated from No. 30 is A 541 x (1-0245)^ -=- (1012) 2 = A 541 x (1-012) 2 
= A554. This doubling of effect on changing from C-substitution to N- 
substitution has already been mentioned under substance No. 9, but it is to 
be noted that phenyl (and probably methyl also) on a linkage has always 
the value 1 026 whether on C or on N. 
(32) Magclala red. — This is safranine with two naphthalene-rings 
attached, and a third in the linkage instead of phenyl. The calculated 
colour of phenyldiaminophenazoniuin salts is A 527, whereas Magdala red 
shows A 559. Assuming that the linkage-naphthyl has the same effect as 
phenyl, this gives a factor of 1*030 for the naphthalene-ring residues, each 
C 4 H 4 . This is a much smaller value than that found from the naphthol- 
phthaleins (1 092), and remains an anomaly until further work can be done 
on naphthalene colours in general.* 
(33) Azine green. — This is about the most complicated member of the 
series. It has the formula : 
NMeo,/ Y . 7 N NHPh 
As shown under No. 32, phenyldiaminophenazonium has A 527. Azine-green 
has, in addition to the latter, a naphthalene-ring, two N-methyls and one 
N-phenyl (value 1 054). Assuming naphthalene to have the normal value 
of 109, because the amino group is outside it in this case, the calculated 
colour of azine-green is 527 X (1-0245) 2 x 1-054 x 1*09 = A 636. I have 
not observed it, but the description in the literature indicates that the 
observed value lies between A 620 and A 640. 
(34) Bioxy anthracene. — The ordinary formula of this substance when 
written hydrated becomes : 
H0 /V CH0H V\0H 
sCH 2 / 
* Since this was written it has been discovered that naphtholphthalein has ortho 
linkages instead of para as hitherto supposed. There is thus no anomaly after all. 
