130 Transactions of the Royal Society of South A frica. 
I have now completed the study of the effect of bromine on colour by 
preparing the phthaleins derived from the brominated phthalic acids, and 
am now able to give a tabular statement showing how the position of the 
bromine atoms affects the colour, and enabling that of any polybromo- 
derivative to be calculated, since the property is additive. 
L5 3j 
Systematic nomenclature of the positions in alkaline plienolphthalein. 
Table giving Value in Colour-change of a Bromine-atom in the Different 
Substituting Positions. 
Position 
Note. — These values are to be 
added to 554 to get the 
wave-length of the ab- 
sorption of the brominated 
phenolphthalein. 
The unit is 1 in the third place of wave-lengths = 10 Angstrom units. 
The positions are not in alphabetical order, but in order of magnitude. 
It is to be noted, however, that the difference between the positions/, 
g, j and k does not come into play unless there is substitution in both rings 
B and B' : thus there is only one mono-orthobromphenolphthalein, which I 
b or 
A4 has 
value 1 ^ 
j 
B'3 
7 i 
Jc „ 
B'5 
7 ' 
c 
A5 
f 
B3 
8 ! 
9 
B5 
„ 8l 
a 
AS 
„ 10 
cl „ 
A6 
„ 10 
i 
B'2 
„ 13 
I „ 
B'6 
„ 13 
B2 
15 
h „ 
B6 
15/ 
