TABLE 5 



Composition of "standard colors" prepared with thymol-blue-acid — range 0.02 



per cent watery solution — range pH 1.4 to pH 2.6 



TABLE 6 



Composition of "standard colors" prepared with brom-phenol-blue* 0.02 per cent 

 watery solution — range pH 3.4 to pH 4-6 



* The blue color of this indicator can be brought out with f n NaOH, but is 

 not lasting and fades within twenty-four to forty-eight hours, while the „^„ 

 NaOH makes a lasting range of "color standards." 



TABLE 7 



Composition of "standard colors" pre pun </ with methyl red 0.02 per cent watery 

 solution — range pH 4-6 to pH 5.8 



* There was a very slight difference between the phthalate NaOH mixture and 

 the "standard colors" in the first three pairs: Pair No. 1 = pH4.7; Pair No. 2 = 

 pH 4.9; Pair No. 3 = pH 5.1 according to the phthalate NaOH mixture, the rest 

 were the same in both. 



457 



