APPENDIX 
Indicator Solutions. The following table is taken from Hawk’s 
Physiological Chemistry and will be found useful in bacterial work. 
The amounts of the indicator solutions and their strengths to be used in 
the determination of hydrogen ion concentrations in 10 c.c. portions 
of unknown solution are indicated below: 
INDICATOR SOLUTIONS 
Drops. Preparation of Solution. 
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pat 
. Alizarin yellow & (p-nitro-~ 
benzine-azo-salicylic acid) | 10-5 | 0.1 gm. in 1000 c.c. water. 
2. Azolitmin (litmus).......] ...... Aqueous solution. 
3. Cochineal...............)....00. Alcoholic solution. 
4, 2.5-dinitro-hydrochinone..| 5-2 | 1 gm. to 1000 ¢.c. alcohol. — 
5. Mauvein.............66. 8-1 | 0.5 gm. to 1000 c.c. 
6. Methyl orange........... 5-3 | 0.1 recrystallized salt to 1000 c.c. water. 
7. Methyl red............. 4-2 | Saturated solution in 50 per cent alcohol. 
8. Methyl violet........... 8~-1 0.5 gm. in 1000 c.c. water. 
9. Neutral red. ............ 20-10 | 0.1 gm. in 500 c.c. alcohol and 500 ec.c. 
water. 
10. p-nitrophenol............ 20-3 | 0.4 gm. to 60 c.c. alcohol, 940 c.c. water. 
11. Phenolphthalein......... 20-3 | 0.5 gm. to 500 c.c. water, 500 c.c. alcohol. 
12. Rosolic acid............. 15-6 | 0.4 gm. in 400 c.c. alcohol, 600 c.c. water. 
13. Thymolphthalein........ 10-3 | 0.4 gm. to 500 c.c. alcohol, 500 c.c. water. 
14. Tropaeolin O............ 10-5 | 0.1 gm. to 1000 c.c. water. 
15. Tropaeolin OO...... ....| & 8 | Of recrystallized salt, 0.1 gm to 1000 c.c. 
water. 
16. TropaeolinOOO......... 10-4 | 0.1 gm. to 1000 c.c. water. 
‘if 
In an extensive study of the application of H-ion determination to 
bacteriological work,.Clark and Lubs (1917 ) have pointed out the 
error in determining reaction by titration. They used the electro- 
metric method and by means of it prepared a series of new indicators 
553 
