METHODS FOR QUANTITATIVE DETERMINATIONS. 269 



Gramme. 



Hydrochloric acid, HC1 0.003637 



Hydrocyanic acid, HCN, to first formation of precipitate . . 0.005396 



Hydrocyanic acid, HCN, with indicator . . . . . 0.002698 



Lithium bromide, LiBr 0.008677 



Potassium bromide, KBr 0.011879 



Potassium chloride, KC1 0.007440 



Potassium cyanide, KCN, to first formation of precipitate . . 0.013002 



Potassium cyanide, KCN, with indicator 0.006501 



Potassium iodide, KI 0.016556 



Potassium sulphocyanate, KCNS 0.009699 



Sodium bromide, NaBr 0.010276 



Sodium chloride, NaCl 0.005837 



Sodium iodide, Nal 0.014953 



Zinc bromide, ZnBr 2 0.011231 



Zinc chloride, ZnCl 2 0.006792 



Zinc iodide, ZnI 2 0.015908 



Deci-normal solution of sodium chloride is made by dissolving 

 5.837 grammes of pure sodium chloride in enough water to make 

 1000 c.c. The titration is made in neutral solution, normal potas- 

 sium chromate being used as an indicator. (See explanation in 

 previous paragraph on silver solution.) 



One c.c. of deci-normal sodium chloride solution, containing 

 0.005837 gramme of NaCl, is the equivalent of: 



Gramme 



Silver, Ag 0.010766 



Silver nitrate,. AgNO 8 0.016955 



Silver oxide, Ag 2 O 0.011564 



Deci-normal solution of potassium sulphocyanate ( Volhard's 

 solution). This solution, like the sodium chloride solution, is used 

 as a companion to silver nitrate ; it has the advantage that it can be 

 used in acid solutions, with ferric ammonium sulphate (ferric alum) 

 as indicator. Silver nitrate forms in the potassium sulphocyanate a 

 white precipitate of silver sulphocyanate : 



KCNS + AgNO 3 = AgCNS + KNO 3 . 



As indicator is used ferric alum, which produces with sulpho- 

 cyanate a deep brownish-red color, which, however, does not appear 

 permanently until all silver has been precipitated. 



As potassium sulphocyanate is rarely pure, 10 grammes, which is 

 about 3 per cent, more than the quantity required, are dissolved in 

 1000 c.c. of water. This solution has to be adjusted by standardizing 

 with deci-normal silver solution until equal volumes decompose one 

 another exactly. 



