140 METALS AND THEIR COMBINATIONS. 



does this solution contain now ?) to dryness, mix the powdered mass with about 

 10 per cent, of powdered charcoal and heat the mixture in a crucible until 

 slight deflagration has taken place. Dissolve the fluid mass in hot water, filter 

 and set aside for crystallization; if too much water has been used for dissolving, 

 the liquid must be concentrated by evaporation. 



Potassium iodide forms colorless, cubical crystals, which are soluble 

 in 0.5 part of boiling and 0.8 part of cold water, also soluble in 18 

 parts of alcohol, and 2.5 parts of glycerin. When heated it fuses, 

 and at a bright-red heat is volatilized without decomposition. 



Potassium bromide, Potassii bromidum, KBr = 118.8 may be 

 obtained in a manner analogous to that given for potassium iodide, 

 by the action of bromine upon potassium hydroxide, etc. 



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

 bromide by potassium carbonate : 



FeBr 2 + K 2 CO 3 = 2KBr -f FeCO 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 con- 

 sidered under the head of their respective acids. Some of these salts are 

 potassium chromate and permanganate, and the salts formed from organic 

 acids, such as potassium tartrate, acetate, etc. 



Analytical reactions. 

 (Potassium chloride, KC1, or nitrate, KNO 3 , may be used.) 



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 platinic chloride and some alcohol : a yellow crystalline pre- 

 cipitate falls, which is a double chloride of platinum and potassium, 

 PtCl 4 (KCl) 2 . 



2KC1 + PtCl 4 = PtCl 4 (KCl) 2 ; 

 2KNO 3 + 2HC1 + Pt01 4 = PtCl 4 (KCl) 2 -f 2HNO 3 . 



The last formula shows the necessity of adding hydrochloric acid, 

 which is not required in case potassium chloride is used. The ad- 

 dition of alcohol facilitates the precipitation of the double chloride 

 of potassium and platinum, because it is less soluble in alcohol than 

 in water. 



2. To a neutral or slightly acid solution of a potassium salt add 

 sodium cobaltic nitrite : a yellow precipitate of potassium cobaltic 

 nitrite, (KNO 2 ) 6 .Co 2 (NO 2 ) 6 -f H 2 O, is produced. (The reaction is 



