72 
Transactions of the Royal Society of South Africa. 
sponding substance without the oxo-linkage is benzaurine, which has A 553. 
Oxo-linkage-factor from (a) = 492 ~ 553 = 0-890. 
(b) Fluorescein = A 494 : corresponding substance = phenolphthalein of 
A 554. Oxo-factor = 494 -*- 554 = 0-892. 
(c) Eosine = X 521, whereas tetrabromophenolphthalein has X 584. Oxo- 
factor = 521 -f- 584 = 0-892. 
(d) Resorcin-sulphophthalein — X 498, compared with phenolsulpho- 
phthalein of X 563 gives the oxo-factor = 0*885. 
(e) The tetrabromo-derivatives (3-3'-5-5') of the foregoing two sub- 
stances have X 527 for the resorcin compound and 594 for the pheuol 
compound. The oxo-factor in this case is 0'887. 
(/) Pyronine has X 542 in alcohol, and Michler's hydrol has X 610 in the 
same solvent. The oxo-factor in this case is 0*889. 
(g) Dioxyxanthhydrol has A 479 in water, and dioxybenzhydrol A 539. 
The oxo-factor for this pair is thus 0*888. 
(h) Tetramethyl-rhodamine has A 553 (same as benzaurine). The corre- 
sponding substance "without the oxo-linkage is " dimethylanilinphthalein," 
which I have not observed. It is related to malachite green just as 
phenolphthalein A 554 is to benzaurine A 553, therefore its A must be that 
of malachite green plus 1 = A 620. Hence the oxo-factor for this pair is 
553 ~ 620 = 0-892. 
(/) Resorufine has A 576: the substance without the oxo-linkage is 
indophenol of A 650. The oxo-factor here is 0 887. 
(j) Hexabromo-derivatives of fluorescein and phenolphthalein substituted 
in the same six places (acfgjk of Part XI) have AA 535 and 602 respectively. 
The oxo-factor from this pair is 0*889. 
(k) Isomeric hexabromo-derivatives derived from 3-6 dibromophthalic 
acid (adfgjk of Part XI) have AA 538 and 606 respectively. This oxo-ratio 
is 0-888. 
The average of these eleven observations gives 0*889 for the oxo-ratio, 
but I am of opinion that much more weight should be given to those 
depending on common substances, and that consequently the true value is 
0-891. 
(2) The thio-linkage. — This could be derived from as many substances as 
the oxo-factor, but the substances, thiofluorescein, thiopyronine, etc., are not 
obtainable or capable of being made here. I have therefore calculated it 
from the methylene-blue and thionol classes alone : 
(a) Methylene-blue and Bindschedler's green have AA 665 and 730 
respectively. The ratio is 0 9 12. 
(b) Thionine and indamine have AA 603 and 660 respectively. The ratio 
is 0 915. 
(c) Thionol and indophenol have AA 593 and 650 respectively. The 
ratio is 0*913, 
