VOLUMETRIC DETERMINATION OF HARIUM AND SULPHATE. I75 



The KgCrO^ solution is prepared by dissolving a ro jghly 

 weighed quantity of pure sulphate free K^CrO^ in sufficieht distilled 

 water to make it tenth-normal, of factor more or less 1.2. The 

 solution should, for convenience, be givep two factors : one, 

 /,, according to the equation — 



2K,^CrO^ + 16HC1 -+- 6KI = 31.^ + lOKCl + 2CrCl3 ; 

 and another, f.^, according to the equation — 



K.^CrO^ + BaCl, ^ BaCrO^ + 2KC1. 



Then obviously /o ^ (f /J, the tenth-normal solution of BaCl.^ 

 , • / mol. weightx .■ 



^'"^( 10 X 2 ) P^'"'^'^- 



Then if we added A cc. of ^^ K.^CrO^ to 50 c c. of the barium 

 salt solution, and we required D cc. of ^n Na.^S^O^ (factor -- V) to 

 remove the liberated iodine, the weight of BaO in 100 cc. of the 

 solution : 



-2 



|_2x /jA--^)x joooJg'^- 



Remark. — If iron is present in the barium solution, it should 

 be separated by NH^Cl and NH^OH in excess, filtering the solution 

 and washing the precipitate, adding the washings to the filtrate. 

 Then proceed as given from (B). 



The method gives results of close agreement, especially if the 

 average of duplicate analyses is taken. 



Working this way, in a solution of BaCU, containing -5028 gm. 

 Ba in 100 cc, was found: — 



1. -5024 gm. Ba in 100 cc j 3. 5023 gm Ba in 100 cc. 



2. -5022 gm. Ba in 100 cc I 4. -5027 gm. Ba in 100 cc. 



A sample of witherite containing, by gravimetric determin- 

 ation, 68-36 per cent. Ba, was found volumetrically to contain; 

 (1) 68-25 per cent. Ba, (2) 6826 per cent. Ba. 



(2) Sulphate. 



Principle. — Excess of a standard /^ BaCl^ solution is added to 

 the neutral or acid sulphate solution, when we have — 



BaCl^ + K^SO^ = BaSO^ + 2KC1. 



The solution is neutralised and excess of standard ^^ K,CrO^ 

 is added, when BaCrO^ is precipitated — 



K^CrO^ + BaCl, = BaCrO^ + 2KCI. 



The excess of K^CrO^ is filtered off, KI and HCl added m 

 excess, and the liberated iodine is titrated with ^^ Na^S^O^. 



Procedure. — From a burette excess of a standard f^ BaCl., 

 solution is run into a measured volume of the sulphate solution. 



