ESTIMATION OF POTASH IN CRUDE POTASH SAI/TS 589 



be contaminated with a trace of phosphoric acid, if the latter be 

 present in large quantity no fear of contamination with mag- 

 nesia need be entertained if a sufficient quantity of the perchloric 

 acid be used. 



493. Removal of the Sulfuric Acid. The practical objec- 

 tion to the removal of the sulfuric acid in the form of barium 

 sulfate rests on -the fact of the mechanical entanglement of some 

 of the potash in the barium salt. Unless special precautions are 

 observed a noticeable amount of the potash will be found with 

 the barium sulfate. 



Caspari has succeeded in reducing this amount to a minimum 

 by the following procedure: 68 The solution of barium chlorid 

 is prepared by dissolving 127 grams of crystallized barium chlorid 

 in water, adding 125 cubic centimeters of 35 per cent, hydro- 

 chloric acid, and bringing the total volume up to one liter with 

 water. 



Five grams of the substance from which the sulfuric acid is to 

 be removed are boiled with 150 cubic centimeters of water and 

 20 of strong hydrochloric acid. While the solution is still in 

 ebullition it is treated, drop by drop, with constant stirring, with 

 the barium chlorid solution above mentioned, until a slight excess 

 is added. This excess does not cause any inconvenience subse- 

 quently. After the precipitation is complete the boiling is con- 

 tinued for a few minutes, the mixture cooled and made up to a 

 quarter of a liter with water. No account is taken of the vol- 

 ume of the barium sulfate formed, since, even with the precau- 

 tions mentioned, a little potassium is thrown down and the vol- 

 ume of the barium sulfate tends to correct this error. With a: 

 solution from which the sulfuric acid had been removed as above 

 indicated, Caspari found a loss of only one milligram of potas- 

 sium perchlorate in a precipitate weighing over 800 milligrams. 



494. Estimation of Potash in Crude Potash Salts by Means 

 of Perchloric Acid. The potash in the raw salt may also be 

 determined by perchloric acid as described below. 69 In the case of 



88 Zeitschrift fur angewandte Chemie, 1893, 6 : 73. 



69 Lunge, Chemisch-technische Untersucliungsmethoden, 5th Edition, 

 1904, 1 : 536. 



