§ 46. SODIUM. 53 



added to convert both the potassium and the sodiuin into 

 the platinic compounds, and the evaporation with platinic 

 chloride should not be carried to complete dryness, so as 

 to avoid expelling the water of crystallization of the so- 

 dic salt. The filtrate from the potassic salt should have a 

 deep yellow color, and the salt, when examined with the 

 magnifier, should be seen to consist only of yellow octa- 

 hedral crystals or a yellow granular powder. 



c. If suljDhuric acid is present in the solution containing 

 sodium and potassium, the conversion of these metals into 

 chlorides may be efiected by gentle ignition with powder- 

 ed ammonic chloride. Evaporate the solution of the sul- 

 phates to dryness, mix the residue with a little more than 

 its weight of jDure ammonic chloride, heat the mixture 

 gently as long as fumes are evolved, and weigh ; add more 

 ammonic chloride to the contents of the crucible, ignite, 

 and weigh again, and r9peat this operation as long as 

 there is any change in weight. 



d. In case the quantity of one metal in the mixture of 

 the chlorides is not very much larger than that of the 

 other, they may be estimated with accuracy by the indi- 

 rect process. Determine the chlorine in the known 

 weight of the mixture by the volumetric process (§ 63, ^), 

 and then calculate the amount of potassium and sodium 

 in it by the following formulas, in which S = the weight 

 of tlce mixture of the chlorides, and A = the amount of 

 chlorine contained therein. 



^ ^ . [(S-A) X 1.54]-A. 



1 otassmm = -^=-^ „ „^ 



O.bd 



e. If it is more convenient to weigh the metals as sul- 

 phates, the sulphuric acid may be determined in the usual 



