568 AGRICULTURAL ANALYSIS 



blackened filtrate doubtless occurs through the action of the 

 oxygen of the air, it was sought to prevent the solution of the 

 platinum beforehand by the use of a substance like nitric acid 

 easily giving off oxygen. 



479. Rapid Control Method for Potash Salts. For rapid con- 

 trol work where great accuracy is not required, Albert recom- 

 mends that the finely ground substance be placed in a liter flask 

 and about 400 cubic centimeters of water added and three cubic 

 centimeters of hydrochloric acid. 48 After boiling, barium chlorid 

 is added, drop by drop, as long as a precipitate is produced. 

 After cooling, the flask is filled to the mark and shaken and its 

 contents filtered through a dry filter. An aliquot portion of 

 the filtrate is evaporated with platinum chlorid solution in a 

 smooth porcelain dish almost to dryness and the mass treated 

 with alcohol, filtered through a weighed filter, and well washed 

 with alcohol. The filter is then dried in an air-bath to a con- 

 stant .weight. For the different kinds of potash materials on the 

 market the following proportions are recommended : 



Kainit or Carnallit. Twenty grams in one liter: Fifty cubic 

 centimeters of the filtrate are evaporated with 40 cubic centime- 

 ters of platinic chlorid solution. The weight of potassium platino- 

 chlorid obtainedXi9-3 gives the per cent, of K 2 O. 



Sulfate of Potash. Fifteen grams in one liter : Twenty cubic 

 centimeters of the solution are evaporated with 15 cubic centi- 

 meters of platinic chlorid. The weight of potassium platinochlo- 

 rid obtained X 64.33 gives the per cent, of K 2 O. 



Potassium Chlorid. Ten grams in one liter. Twenty-five cub- 

 ic centimeters are evaporated with 15 cubic centimeters of platinic 

 chlorid solution. The weight of the precipitate obtained X 77-2 

 gives the per cent, of K 2 O. 



480. Weighing the Precipitate as Metallic Platinum. Hilgard 

 calls attention to the difficulty of weighing the double chlo- 



48 Zeitschrift fur angewandte Chetnie, iSgr, 4 : 281. 



