120 METALS AND THEIR COMBINATIONS. 



The cooled mass is dissolved in hot water, filtered, and crys- 

 tallized, when potassium iodide is obtained in colorless, cubical 

 crystals, which are very soluble in water. 



Potassium bromide, Potassii bromidum, KBr = 118.8 (Bromide of 

 potassium), may be obtained in a manner analogous to that given 

 for potassium iodide, by the action of bromine upon potassium 

 hydrate, etc. 



Or it may be made by the decomposition of a solution of 

 ferrous bromide by potassium carbonate : 



FeBr 2 -f K 2 CO 3 = 2KBr + FeC0 3 . 



Ferrous carbonate is precipitated, whilst potassium bromide 

 remains in solution, from which it is obtained by crystallization. 



Potassium salts of interest, which have not yet been mentioned, 

 will be considered under the head of their respective acids. 

 Some of these salts are the potassium chromate and permangan- 

 ate, and the salts formed from organic acids, such as potassium 

 tartrate, acetate, etc. 



Analytical reactions. 



1. To a solution of potassium chloride, or to any salt of potas- 

 sium, after a few drops of hydrochloric acid have been mixed 

 with it, add platinum chloride and some alcohol: a yellow crys- 

 talline precipitate falls, which is a double chloride of platinum 

 and potassium, PtCl 4 2KCl. 



2. Add to a concentrated solution of a potassium salt strong 

 solution of tartaric acid: a white precipitate of potassium acid 

 tartrate is slowly formed. 



3. Potassium compounds color the flame of a Bunsen-burner 

 or of alcohol violet. (Presence of sodium interferes with this 

 flame-test.) 



4. All compounds of potassium are white (unless the acid has 

 a coloring effect), soluble in water, and not volatile at a low 

 red heat. 



