136 CONN, HARDING, KLIGLER, FROST, PRUCHA AND ATKINS 



reaction of the culture to litmus, than to use the titration method. 

 Under such conditions it is possible, however, to obtain a rough 

 idea of the hydrogen-ion concentration by the use of Clark and 



TABLE 1 

 Degrees of acidity easily recognized in clear media 



"Neutral". 



"Weak' 



"Moderate" 



"Strong" J 



"Very strong" 



INDICATOR REACTIONS 



Blue or green to brom thymol blue* 



Yellow to brom thymol blue 

 Purple to brom cresol purple* 



Yellow to brom cresol purple 

 Orange to methyl redf 



Maximum red to methyl red 



Blue or green to brom phenol blue* 



Yellow to brom phenol blue 



APPROXIMATE 

 pH-VALUE 



Over 6.2 

 5.2-6.0 



i 4.6-5.0 



3.2-4.4 

 Under 3.0 



* Use a 0.04 per cent alcoholic solution. 

 t Use a 0.02 per cent alcoholic solution. 



TABLE 2 

 Degrees of acidity easily recognized in milk 



* Use a 0.04 per cent alcoholic solution. 



Lubs' series of indicators without making accurate determinations 

 of pH. Four different degrees of acidity can be easily distin- 

 guished by this simple method in sugar broth with an initial 

 reaction of neutrality. The indicator reactions for these differ- 



