116 METALS AND THEIR COMBINATIONS. 



phosphates, and sulphates of calcium and magnesium, silica, 

 etc.) is left behind, whilst a lye is obtained containing the 

 soluble constituents, of which potassium carbonate is the prin- 

 cipal one, chlorides and sulphates of potassium and sodium 

 being also present in small quantities. 



By evaporation of this lye to dryness an impure potassium 

 carbonate is obtained, which is sold as crude potash. 



Up to within twenty years ago the chief supply of potash was 

 obtained by this process, and the trees of thousands of acres 

 were burned with the view of obtaining potash. To-day this 

 mode of manufacturing potash is very limited and is rapidly 

 decreasing, as, fortunately, a new supply of soluble potassium 

 salts has been discovered in the salt-mines of Stassfurt, Ger- 

 many, where large quantities of potassium chloride (and some 

 sulphate) are found, from which the carbonate and other salts 

 are manufactured. 



Potassium hydrate, Potassa, KHO = 56 (Caustic potash], may 

 be obtained by the action of the metal on water : 



K + H 2 O = H + KHO. 



The usual process for making potassium hydrate is to boil to- 

 gether a dilute solution of potassium carbonate or bicarbonate 

 and calcium hydrate : 



K 2 CO 3 + Ca2HO = CaC0 3 + 2KHO. 



The two metals exchange places, insoluble calcium carbonate is 

 formed, which gradually subsides, whilst the liquid contains 

 potassium hydrate. By evaporation to dryness the solid com- 

 pound is obtained. 



Potassium hydrate is a white, hard, solid substance, soluble 

 in 0.5 part of water and 2 parts of alcohol ; it fuses at a low 

 red heat, forming an oily liquid, which may be poured into 

 suitable moulds to form pencils; at a strong red heat it is 

 slowly volatilized without decomposition ; it is a very strong 

 base, readily combining with all acids ; when taken internally 

 it acts as a powerful corrosive, and most likely also as a poison. 



Antidotes : dilute acids, vinegar, to form salts ; or fat, oil, or 

 milk, to form soap. 



