504 APPENDIX 
which will be valuable in future bacteriological work. They are given 
in Table LIT. 
TasBue LIT 
LIST OF INDICATORS, PREPARED BY CLARK AND LUBS, 1918 
Concen- 
Chemical Name. Common Name. tration, | Color Change. Range 
Per Cent. 
Thymol sulphon phthalein (acid range) | Thymol blue...... 0.04 Red-yellow 1.2-2.8 
Tetra bromo phenol sulphon phthalein}; Brom phenol blue 0.04 Yellow-blue 3.0-4.6 
Ortho carboxy benzine azo di methyl 
aniline... . cc ee ee eet ees Methyl red....... 0.02 Red-yellow 4.4-6.0 
Ortho carboxy *benzine azo di propyl . 
ANUINE. . ee eee eee Propyl red........ 0.02 Red-yellow 4,8-6.4 
Di bromo ortho cresol sulphon phtha- 
Wein. eee tenes Brom cresol purple 0.04 Yellow-purple | 5.2-6.8 
Di bromo thymol sulphon phthalein. | Brom thymol blue. 0.04 Yellow-blue 6.0-7.6 
Phenol sulphon phthalein............ Phenol red........ 0.02 Yellow-red 6.8~8.4 
Ortho cregol sulphon phthalein....... Cresol red........ 0.02 Yellow-red 7.2-8.8 
Thymol sulphon phthalein (see above).| Thymol blue...... 0.04 Yellow-blue 8.0-9.6 
Ortho cresol phthalein.............. Cresol phthalein. .. 0.02 Colorless-red 8.2~-9.8 
PREPARATION OF STANDARD REAGENTS 
A standard solution contains a known amount of reacting substance 
and is to be distinguished from a normal solution. A normal solution 
contains the hydrogen equivalent of the active constituent in grams per 
liter. This is that amount which brings into the reaction 1.008 gms. of 
hydrogen, 8 gms. of oxygen, etc., or the equivalent. This definition has 
so many distinct advantages that it is now generally accepted. 
The following are some of the standard solutions used in bacteriology: 
N Sodium Hydroxide. Weigh out 40.06 or better about 45 gms. of 
sodium hydroxide and dissolve in 1 liter of boiled cooled distilled water. 
Standardize against normal hydrochloric acid. It is best to allow the 
two solutions to stand at the same temperature for several hours or 
overnight. The titration should be repeated several times. Calcula- 
tion is as follows: 
If 50 c.c.NaOH=52.6 cc. NHCl 
the NaOH is too strong by 2.6 ¢.c. per every 50 c.c. 
_2.6X 1000 _ 
50 : 2.6=1000 : : 
1000: 2 20 
50.¢.¢. 
