POTASSIUM. 29 



Characters. Dark-purple slender prisms, 

 inodorous, with a sweet astringent taste. Solu- 

 ble in 16 parts of cold water. Should be pre- 

 scribed in simple solution. 



Impurities. Sulphate of potash and oxide 

 of manganese; detected by less solubility in 

 water and volumetric test. 



Dose. 1 to 2 gr. 



Preparation. 



Liquor Potassae Permanganatis. 4 gr. in 

 1 fl.oz. of distilled _ water. Dose, 2 to i tl. 



j3. Potassii lodidum. Iodide of Potassium 

 KI. 



Source. Obtained by dissolving Iodine in 

 Liquor Potassae, and evaporating 6KHO+3I 2 =:5KI 

 + KI0 3 + 3H 2 ; then mixing the residue with 

 wood charcoal, fusing, dissolving, and purifying, to 

 convert the iodate, which was formed with the 

 iodide, into iodide 2KI0 3 -f 60 = 2KI + 6CO. 



Characters. Colourless opaque cubical crystals, 

 with some odour of iodine, a saline taste, and feebly 

 alkaline reaction; strikes blue with preparations 

 containing starch on addition of chlorine. 



Impurities. Iodate; detected by blue colour 

 with tartaric acid and starch. Free iodine ; by starch. 

 And the impurities of the liquor. 



Dose. 2 to 10 gr., or more. 



For Preparations, see lodum. 



y. Potassii Bromidum. Bromide of Potas- 

 sium. K5r. 



Source. Obtained from Liquor Potassae, Bro- 

 mine, and Charcoal, by the same process as the 

 iodide. 



Characters. Colourless cubic crystals, without 

 odour, and of a pungent saline taste. Does not 

 strike blue with preparations containing starch, 

 unless it contain iodide as impurity. 



Dose. o to 30 gr. 



e. Potassae Citras. Citrate of Potash. K 3 C 6 H S 7 . 



Source. Made by neutralising a solution of Citrici 

 Acid with Carbonate of Potash, and evaporating. 3K CO 3 

 + 2C 6 H 5 O 7 , H 3 = 2K 3 C 6 H 5 7 + 3H 2 O + aCO^ 



