INSTRUMENTS AND < ni.MK'Ai. Ti:sTS :><;:< 



heat of the ( ). 1'. ; t In- acid radicle is partially or completely v.olaiil- 

 lied, 



Potassium, K. Atomic weight, 39.10. Fusing point, 02.5 C. 



a. Compounds <>f potassium, except silicates, phosphates, ami 

 bo rates, when heated on Wire or in the forceps yield ;i light, violet 

 tlame. When Sodium OF lithium is present, the potassium flame i- 

 masked. In such cases the flame is viewed through the blue cobalt 

 glass, which if dark enough absorbs the sodium and lithium flames 

 but allows the violet rays of potassium to pass through. In place 

 of the blue glass a clear bottle, with flat sides, filled with a solu- 

 tion of potassium permanganate, or better still, a solution of chrome 

 alum, will serve the same purpose. The required depth of color 

 is obtained by experimenting with solutions of different strengths. 

 After a time the permanganate, by decomposition, deposits a 

 brown film on the walls of the bottle ; from this fault a solution of 

 chrome alum is free. Viewed through all these media the potas- 

 sium flame is violet-red. 



Illustration. Heat some sylvite, KC1, on platinum wire hi 

 O. F. and observe the violet flame, also through the blue glass. 



6. In case of silicates, borates, and phosphates, the finely ground 

 mineral is mixed to a stiff paste with water and four parts of 

 potassium flux. It is then fused in the blue mantle of the Bunsen 

 burner flame ; the violet-red of potassium will appear through the 

 blue glass. 



Illustration. Powder some orthoclase, KAlSisOs, in the agate 

 mortar ; add four parts of potassium flux and water to a stiff paste. 

 Hold the mixture on platinum wire in the Bunsen burner flame al >< >ut 

 halfway up and on the side ; observe the potassium flame through 

 the blue glass, when it will appear violet-red. 



c. Platinum chloride test. If to a slightly acid solution of 

 potassium salts hydrochloro-platinic acid, H 2 PtCl 8 , is added, the 

 solution evaporated nearly to dryness, then diluted with alcohol, 

 the potassium will separate as yellow octahedral crystals of potas- 

 sium platinic chloride, K 2 PtCl 6 . The corresponding sodium salt 

 is soluble in alcohol. Ammonium, lithium, rubidium, and caesium 

 yield similar precipitates insoluble in alcohol. 



Illustration. Dissolve a little sylvite in water, add a drop of 

 HC1, and precipitate with K 2 PtCl 6 and alcohol. 



Insoluble silicates must be fused with soda. Fuse 1 part of finely 

 powdered orthoclase with 5 parts of soda, either make several beads 

 on wire, or fuse on platinum foil. The fusion is boiled in water, 



