ROCHELLE-SALT. 17 



dried at 100, and weighed. 100 parts correspond to 

 16.03 of potassium, or 19.33 of potassa. 



The amount of the chloride of sodium may be 

 ascertained by deducting the weight of the chloride of 

 potassium from that of the mixed chlorides. It is 

 safer, however, to control this result by direct deter- 

 mination, for which purpose the filtered liquid is care- 

 fully evaporated to dryness, and the mass strongly 

 ignited in a covered platinum crucible; in order to 

 insure the complete decomposition of the chloride of 

 platinum, the ignition should be repeated, with addi- 

 tion of a few crystals of oxalic acid. From the cooled 

 mass, the chloride of sodium is extracted with water. 



When, as is frequently the case, the two alkalies 

 are present as sulphates, together with an excess of 

 acid, the greater portion of the latter is expelled by 

 careful evaporation, and the saline mass afterwards 

 ignited in a covered platinum crucible, into which 

 small fragments of carbonate of ammonia are from 

 time to time introduced. The joint weight of the 

 neutral salts thus obtained is then determined. 



In order to convert these sulphates into chlorides, 

 the mass is moistened with water, mixed with pure 

 chloride of ammonium, and heated in a covered cru- 

 cible until the excess of the latter salt is expelled ; 

 this operation is repeated until the weight is constant, 

 when the chlorides are separated by means of bichlo- 

 ride of platinum. 



Or the solution of the sulphates maybe precipitated 

 by a solution of pure acetate of baryta, the precipitate 

 filtered off) the filtrate evaporated to dryness, and the 

 residue ignited. From the carbonized mass, water 

 dissolves the alkalies as carbonates, which are con- 

 verted into chlorides by treatment with hydrochloric 

 acid. 



2* 



