182 Wisconsin Academy of Sciences, Arts, and Letters. 
The indicators used were of U. S. P. strength. Those not offi¬ 
cial were prepared according to a table given by Clark and Lub. 107 
The following table represents the results obtained. 108 
Indicator 
p. c. 
No. 1 
No. 2 
No. 3 
No. 4 
No. 5 
No. 6 
Cresol red .. 
.04 
acid— 
alkaline 
do. 
do. 
do.+ 
neutral 
Phenol red . 
.04 
acid— 
alkaline 
do. 
do. 
do. 
neutral 
Brazil wood . 
u. s. 
acid 
alkaline 
do. 
do. 
do. 
neutral 
Litmus . 
u. s. 
acid 
alkaline 
do. 
do. 
do. 
neutral 
Hematoxylin ... 
u. s. 
acid 
alkaline 
do.+ 
do.+ 
do.-f 
neutral 
Brom-cresol—purple .. 
.04 
neut. 
alkaline 
do. 
do. 
do. 
neutral 
Brom-thymol—blue ... 
.04 
neut. 
alkaline 
do. 
do. 
do. 
neutral 
Rosolic acid .. 
u. s. 
neut. 
alkaline 
do. 
do. 
do. 
neutral 
Thymol blue . 
.04 
neut. 
alkaline 
do. 
do. 
do. 
neutral 
Phenolphthalein. 
1.0 
“neut.” 
alkaline 
do. 
do. 
do. 
109 neutral 
Cochineal . 
u. s. 
neut. 
alkaline 
do.+ 
do. 
do. 
neutral 
Alkali blue . 
0.5 
neut. 
alkaline— 
do.+ 
do.+ + 
do.+ 
neutral 
Methyl red . 
0.2 
neut. 
alkaline 
do. 
do. 
do. 
neutral 
Par a-nitro-phenol ..... 
1.0 
neut. 
alkaline 
do. 
do. 
do. 
neutral 
Congo red . 
0.5 
neut. 
alkaline 
do.— 
do. 
do. 
neutral 
Turmeric. 
U. S. 
neut. 
alkaline 
do. 
do. 
do 
neutral 
Methyl orange. 
0.1 
no distinction in color of soli 
jtions 
Btom-phenol—blue. 
0.4 
no distinction in color of solutions 
Iodeosin . 
0.1 
no distinction in color of solutions 
Eosin .. 
0.1 
no distinction in color of solutions 
A survey of the table reveals that only six out of twenty indica¬ 
tors show an acid reaction towards an aqueous solution of arsenic 
trioxide. Three of these viz. litmus, turmeric and hematoxylin are 
plant pigments, the composition of which is not well understood. 
The other three phenol red and cresol red are phenol-sulphone- 
phthalein, and ortho-cresol-sulphone-phthalein respectively, and 
phenolphthalein. 
A peculiar change was noticed in the two series of solutions con- 
107 Journal of Bacteriology, vol. 2, p. 1 (1917.) 
108 Tube No. 6 (H 2 0) was taken as a standard, i. e. it was considered neutral, 
and any other tube showing same color was considered neutral. 
109 Phenolphthalein naturally does not reveal the acid reaction of the As 2 O s 
solution. 
