162 Transactions of the Royal Society of South Africa. 
It is probably unnecessary to describe the method of preparation of 
any of these substances, the information in Part XI about derivatives of 
phenolphthalein sufficing by analogy. It may be noted also that positions 
f and g are radically different in fluorescein, although they are almost the 
same in phenolphthalein. I have assumed, in assigning constitutions to 
these substances, that a substituent will enter the g and j positions firsts 
since the other two or^o-positions, f and k, are " protected " by the oxo- 
linkage. 
Deductions from the Observations. 
A. The observations become consistent for the four " phthalic " 
positions, a, b, c, and d, if we assume a-monobromo- = d-monobromo- 
= +8, and also assume 6-monobromo- to have no effect, and c-monobromo- 
= +4J. 
Hence a-monobromc colour-factor in fluorescein = 1-01 62 
b- „ „ „ =1-0000 
c- „ „ „ =1-0091 
d- „ „ „ =1-0162 
These four factors therefore are smaller than those obtained for phenol- 
phthalein, but their mutual variations resemble those of the phenolphthalein 
series, and the actual discrepancy is not much more than 1 part in 500, 
or than the error of observation. It follows therefore that the phthalic 
part of the fluorescein molecule does not differ much spatially from the 
phthalic part of the phenolphthalein molecule. 
B. It has been impossible to make monobromo-compounds of the 
fgjk class, but by difference I estimate that f-bromo = k-bromo= +6, and 
that g-bromo=j-bromo = 7f. 
Hence f-monobromo colour-factor in fluorescein = 1-0122 
g- „ „ „ =1-0157 
j- „ » „ =1-0157 
k- „ „ „ =1-0122 
These four factors are not smaller than those obtained for phenol- 
phthalein, and vary irregularly like an . experimental error: nevertheless 
I think the small differences are real, and are due to the presence of the 
oxo-linkage. 
As already stated, the h and i bromo colour-factors could not be 
ascertained by direct experiment. By inference from y-orcinphthalein 
and phloroglucin-phthalein, however, I find them to be less than unity, 
viz. both the A-monobromo and the *-monobromo colour-factors are 
