PART III 



QUALITATIVE AND QUANTITATIVE METHODS OF 



ANALYSIS 



PREPARATION OF REAGENTS 



Prepare stock solutions of the indicators in dropping bottles. 



Phenolphthalein. — Dissolve 1 gram of pure phenolphthalein in 

 100 cubic centimeters of 86 per cent alcohol. This indicator 

 is recommended for the titration of organic and inorganic acids 

 and strong bases. It should not be used for the titration of 

 ammonia. 



Methyl Orange. — Dissolve 0.02 gram of solid methyl orange 

 in 100 cubic centimeters of hot water, allow to cool, and, if a 

 deposit forms, filter. If the sodium salt is used instead of the 

 acid, take 0.022 gram to 100 cubic centimeters of water. Add 

 0.67 cubic centimeters of 0.1 N hydrochloric acid, let stand, and 

 filter. Methyl orange is used for the titration of strong acids. 



Litmus. — This indicator is obtained from a species of lichen. 

 It is widely used in bacteriology, especially in milk. The chief 

 coloring principle is azolitmin. Dissolve 5 grams of purified 

 litmus in 100 cubic centimeters of water. Heat in the steamer 

 for 1 to 2 hours, with occasional shaking. Allow to settle for 

 several days and then decant the clear liquid. 



Cochineal. — Take 6 grams of cochineal to 50 cubic centimeters 

 of alcohol (95 per cent) and 200 cubic centimeters of distilled 

 water. Shake the cochineal in the mixture of water and alcohol. 

 Allow to stand for two days at room temperature. Filter until 

 clear. The color of this solution should be a deep ruby red; in 

 the presence of alkali a violet color, and in the presence of acid 

 a yellowish-red color. 



Sodium Alizarine Sulfonate. — Dissolve 1 gram in 100 cubic 

 centimeters of distilled water by warming. Filter and make 

 up to volume. 



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