CASPARI'S METHOD 581 



heated, with vigorous stirring, to boiling, with one and a half 

 times their weight of water. By this process the potassium 

 chlorid which has formed during the first reaction is dissolved 

 and is thus removed. The residual salt is washed with addi- 

 tional quantities of cold water and finally dried. To remove the 

 potassium base from the crude potassium perchlorate obtained as 

 above, recourse is had to hydrofluosilicic acid. The reaction is 

 represented by the following formula: 2KClO 4 -j-tI 2 SiF 6 K 2 SiF 6 

 -|-HC1O 4 . In order to effect this decomposition the potassium 

 perchlorate is dissolved in seven times its weight of hot water 

 and an excess of hydrofluosilicic added to the boiling solution. 

 A porcelain dish may be used. The boiling is continued, with 

 addition of water to compensate for evaporation, for about an 

 hour until particles of potassium perchlorate can no longer be 

 detected. 



On cooling, the gelatinous potassium silicofluorid is deposited 

 and the perchloric acid separated therefrom as completely as pos- 

 sible by decantation. The residue is again boiled with water and 

 a little hydrofluosilicic acid and the clear liquor thus obtained 

 added to the first lot. The second boiling may generally be omit- 

 ted. Finally, any residual perchloric acid may be removed on 

 an asbestos felt under pressure. The clear liquid thus obtained 

 is evaporated on a steam-bath to the greatest possible degree of 

 concentration and allowed to stand in a cool place for 24 hours, 

 whereby is effected the separation of any remaining potassium 

 silicofluorid or potassium perchlorate. The residual liquid when 

 filtered through an asbestos felt should give a perfectly clear fil- 

 trate. In order to throw out the last traces of hydrofluosilicic 

 acid and any sulfuric acid present, an equal volume of water is 

 added, and while cold small quantities of barium chlorid are suc- 

 cessively added until the barium salt is present in a very slight 

 excess. The clear supernatant liquid is poured off after a few 

 hours and evaporated until the acid is all expelled and white 

 fumes of perchloric acid are noticed. Any potassium perchlorate 

 still remaining will now be separated and, in the cold, sodium 

 perchlorate will also be separated in crystals. The clear residue 

 is again diluted with an equal volume of water and any barium 



