456 LEON S. MEDALIA 



Thymol-blue-alkaline-range. The extreme acid (yellow) color 

 was brought out by using 0.001 per cent HC1; the extreme alka- 

 line ( blue) color of this indicator was brought out by the use of 

 fs NaOH. 



Brom-phenol-blue. The extreme acid (yellow) color of this 

 indicator was brought out by 0.1 per cent HC1; the extreme alka- 

 line (blue) color was brought out by ^o NaOH solution, instead 

 of & NaOH. 



Methyl-red. The extreme acid (red) color of this indicator, was 

 brought out by 0.1 per cent HC1; the extreme alkaline (yellow) 

 color of this indicator was brought out by -^ NaOH. 



Brom-cresol-purple. The extreme acid (yellow) color of this 

 indicator was brought out by 0.1 per cent HC1; the extreme alka- 

 line (purple) color was brought out by £> NaOH. 



Brom-thymol-blue. The extreme acid (yellow) color of this 

 indicator was brought out by 0.1 per cent HC1; the extreme alka- 

 line (blue) color was brought out by ^ NaOH. 



Phenol-red. The extreme acid (yellow) color of this indicator 

 was brought out by 0.1 per cent HC1; the extreme alkaline (red) 

 color was brought out by £> NaOH. 



Cresol-red. The extreme acid (yellow) color of this indicator 

 was brought out by 0.1 per cent HC1; the extreme alkaline (red) 

 color was brought out by ^ NaOH. 



The procedure is the same as described under part I — seven 

 pairs of tubes are filled, each with 10 cc. amounts of the respec- 

 tive acid and alkaline solutions for each indicator. The seven 

 alkaline (or weak acid) tubes are set up in a row behind the seven 

 acid tubes. The indicator solution is added to the akaline tubes 

 in amount of 0.1 cc. increasing by 0.1 cc. up to 0.7 cc. from left 

 to right — while in the acid row of tubes, 0.7 cc. indicator solution 

 is added decreasing from left to right by 0.1 cc. down to 0.1 cc. 

 in the last tube. In case it is desired to keep the color standards 

 for any length of time, it is best to stopper the tubes with cork 

 stoppers previously dipped in hot melted paraffin. Solutions 

 treated as just described, have been found to keep well for over 

 three months. It is well to check up these "standard colors" 

 by setting up fresh sets, for the purpose, once a month, or oftener. 

 This can be done very easily and does not take up much time. 



