56 



PRACTICE 26. (Con't) 



wash with hot water until free of chlorids. Dissolve the precipitate from 

 the filter with as small an amount as possible of warm dilute sulfuric acid 

 (i to 6), catch the solution and washings in a 200 cc. Erlenmeyer flask and 

 treat this solution as directed below for the determination of iron. 



Concentrate the filtrate from the barium hydroxid precipitation to about 

 50 cc., add a few drops of ammonium hydroxid and 10 cc. of ammonium 

 carbonate solution, let stand 30 minutes on the water-bath, filter through 

 an ii cm. filter into a 10 cm. evaporating dish, and wash with hot water 

 until free of chlorids. Evaporate the filtrate to dryness and carefully ig- 

 nite the dish over a Bunsen burner to expel ammonium salts. Take up 

 with about 10 cc. of hot water, add a few drops of ammonium hydroxid 

 and ammonium carbonate, filter through a 9 cm. filter into a 250 cc. 

 beaker, and wash with hot water. Concentrate to about 25 cc., add 5 cc. 

 of ammonium sulfate solution (75 gm. per liter), digest on a water-bath 2 

 hours, and filter into a 250 cc. beaker through a 9 cm. filter. Transfer to a 

 small weighed evaporating dish or large crucible, and evaporate to dryness. 

 Ignite over a Bunsen burner to remove ammonium salts. Add I gm. of 

 powdered ammonium carbonate, heat to full redness, cool in a desiccator, 

 and weigh. 



Weight of dish plus K 2 SO 4 and Na 2 SO 4 



Weight of dish 



Weight of K 8 8O 4 and Na 2 80 4 



Weight of K..SO 4 (computed) 



Weight of Na 2 SO 4 



Weight of Na 



Percent Na 



Average 



Take up with a little hot water, add a few drops of hydrochloric acid 

 and platinic chlorid solution (10 cc. contain I gm. platinum), using .1 cc. of 

 the platinum solution for every 5 mg. of sulfates found, evaporate to a 

 thick syrup, wash seven times with 4 cc. of 80% alcohol, decanting each 

 time through a 9 cm. filter, let the filter dry thoroughly at room tempera- 

 ture, and dissolve any of the potassium platinic chlorid on the filter with 

 hot water, catching the solution in the dish containing the greater part of 

 the salt, evaporate to dryness, heat 30 minutes at IIO Q in an air-bath, cool 

 in the desiccator, and weigh. 



Weight of dish plus K a PtCl 6 



Weight of dish 



Weight of K 2 PtCl 6 



Weight of K 



Percent of K 



Average 



To the 200 cc. Erlenmeyer flask, containing the iron in sulfuric acid 

 solution, add i gm. of zinc dust, stopper with a cork carrying a delivery- 

 tube bent so as to dip into a beaker of distilled water. Let stand over 

 night and titrate the reduced iron with potassium permanganate. (Solu- 



