94 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



COLOR CHANGES OF CLARK AND LUBS INDICATORS 



intensity of the color change from yellow to blue with stan- 

 dard solutions whose pH values are known. 



In figure 48 is given diagrammatically a scale of pH 

 values from 1 to 14. This scale is designated to the left. 

 To the right are designated the pH values of certain solu- 

 tions and of media commonly used in the laboratory. The 

 heavy portions of the lines designating the indicators show 

 those particular ranges in which the color changes are most 

 rapid. It should be remembered that a decrease of 1 in 

 pH value multiplies the hydrogen ion concentration by 

 ten. A pH of means normal concentration of hydrogen 

 ions, and a pH of 14 a normal solution of hydroxyl ions. 





