rather than by the difficult analyses of the respective cations. 10 ml. 

 of the unknown is pipetted into a 125 ml. erlenmeyer, diluted to 50 ml., 

 and titrated with standard silver nitrate (about 1 molar), using three 

 drops of dichlorof luorescein indicator. The titration must be done as 

 rapidly as possible to avoid masking of the end-point by the purple color 

 of reduced silver. The end-point is taken as the first persistent salmon- 

 pink color in the mixture. 



The indicator is prepared by dissolving 0.1 g. of dichlorof luorescein 

 and 2.5 ml. of O.IN NaOH in 100 ml. of distilled water, and does not work 

 in acid solutions below pH 5.5. The silver nitrate is standardized by 

 titration against accurately weighed 1.1-1.2 g. samples of reagent sodium 

 chloride. The NaCl is placed in a 125 ml. erlenmeyer, dissolved in 50 ml. 

 of distilled water, and titrated by the same method as is used on the un- 

 knowns. It will take about 20 ml. of silver nitrate to titrate NaCl sam- 

 ples of the recommended amount. 



Weight : Volume Factors for Salt Standards 



1.000 Molar gms./ml. ml. /gram 



NaCl 0.05845 17.11 



KCl 0.07456 13.42 



CaCl2»2H20 0.14703 6.81 



MgCl2*6H20 0.20333 4.92 



MgS04.7H20 0.24649 4.06 



NaHCOg 0.08402 11.91 



Solutions Isotonic with Sea Water Salinity 35 °/oo 



NaCl 0.53M 



KCl 0.53M 



CaClg* 2H2O . 34M 



MgClg* 6H2O 0. 37M 



MgS04« 7H2O 0. 90M 



NaHCOg 0.54M 



NaBr 0. 54M 



Na2SO4+10H2O 0. 44M 



CsCl 0.53M 



RbCl 0.58M 



LiCl 0.60M 



C,2H220n 0.81M 



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