POTASSIUM. 139 



Potassium sulphate exists in small quantities in plants, and in 

 nearly all animal tissues and fluids, more abundantly in urine. 



Potassium hydrogen sulphate, bisulphate, or potassium add sulphate, 

 may be obtained by the action of one molecule of potassium chloride 

 upon one molecule of sulphuric acid : 



KC1 + H 2 S0 4 = HC1 + KHSO 4 . 



Potassium sulphite. Obtained by the decomposition of potassium carbonate 

 by sulphurous acid : 



K 2 C0 3 + H 2 S0 3 = H 2 + C0 2 + K 2 S0 3 . 



Potassa Sulphurata, U. S. P. (Sulphurated potassa, Liver of sulphur, Hepar 

 sulphuris}. A mixture of potassium sulphide, polysulphide, and thiosulphate. 

 It is made by heating a mixtur^ of one part of sulphur and two parts of potas- 

 sium carbonate in a covered crucible, and pouring the fused mass on a marble 

 slab: 



3K 2 C0 3 + 8S = K 2 S 2 3 + 2K 2 S 3 + 3CO 2 . 



The freshly prepared substance has a liver-brown color, turning gradually to 

 greenish yellow ; it is very apt to absorb water and oxygen, both the sulphide 

 and hyposulphite becoming oxidized, and finally converted into sulphates. 



Potassium hypophosphite, Potassii hypophosphis, KPH 2 O 2 = 

 104, may be obtained by decomposing a solution of calcium hypo- 

 phosphite by potassium carbonate : 



Ca(PH 2 O 2 ) 2 + K 2 CO 3 = 2KPH 2 O 2 + CaCO 3 . 



The filtered solution is evaporated at a very gentle heat, stirring 

 constantly from the time it begins to thicken until a dry, granular 

 salt is obtained, which is soluble in 0.6 part of cold and 0.3 part of 

 boiling water. 



Potassium iodide, Potassii iodidum, KI = 165.5 is made by the 

 addition of iodine to a solution of potassium hydroxide until the 

 dark -brown color no longer disappears : 



6KOH + 61 = 5KI + KIO 3 + 3H 2 O. 



Iodide and iodate of potassium are formed, and may be separated 

 by crystallization. A better method, however, is to boil to dryness 

 the liquid containing both salts, and to heat the mass after having 

 mixed it with some charcoal, in a crucible, when the iodate is con- 

 verted into iodide : 



KIO 3 + 30 = KI + SCO. 



Experiment 17. Add to a solution of about 3 grammes of potassium hydroxide 

 in about 25 c.c. of water (or to the solution obtained by making Experiment 

 16) iodine until the brown color no longer disappears. (How much iodine will 

 be needed for 3 grammes of KOH ?) Evaporate the resulting solution (What 



