63 
Transactions of the Royal Society of South Africa. 
(16) Pyronine. — This lias the formula : 
NMe 2 : 
NMe, 
It is calculated by multiplying A 1548 (for the dimethylaniline rings) by 
factors C and E, viz. 1548 x 0 89 x 0 39 = A 536. Observed X 542 in 
alcohol. 
(17) Rhodamine.— This is the benzoic-acid derivative of pyronine (cf. 
phenolphthalein). The benzoic factor is 1 028 (see p. 67). The calculated 
X is 536 x 1-028 = X 552. Observed X 553. 
(18) Dioxyxanthhydrol. — This is pyronine with 20H instead of 2NMe 2 . 
Calculated 1380 x 0'89 x 0 39 = X 478. Observed A 479. This substance 
is the parent of fluorescein. 
(19) Fluorescein. — The above plus benzoic acid is fluorescein. Calculated 
478 x 1 028 = X 492. Observed X 494. 
(20) Eosine. — This is fluorescein plus four ortho-bromines. Calculated 
X = 492 x (1-0128) 4 (see Part IX) = X 519. Observed X 521. 
(21) Resorufine. — This has the formula : 
X 1380 for the phenol rings is therefore multiplied by factors C and G-. 
The result is 1380 x 0*89 x 0-47 = X 577. Observed X 576. 
(22) Thionol. — This is the foregoing Avith S in place of O. The calculated 
value is 1380 x 0*92 x 047 = X 597. Observed X = 593. 
(23) Methyl ene-blue. — This is the example given in the Addendum to 
Part X. It is thionol with two dimethylaniline rings instead of two phenol 
rings. Calculated 1548 x 0-92 x 0-47 = A 668. Observed A 665. Formanek 
gives A 66 7 ^ in what was probably a better specimen. 
(24) Thionine. — This has the formula : 
Calculated value = 1400 (for two aniline rings) x 0*92 x 0 47 = A 604. 
Observed A 603. 
(25) Gentianine. — This is halfway between Nos. 23 and 24 in constitution. 
Since the scheme is factorial its calculated A is the geometric mean (not the 
arithmetical mean) of the AA of Nos. 23 and 24 — A 635. Formanek observed 
A 638. 
