Potassium cyanide (KCN). When animal matter containing nitrogen is heated with iron and potassium carbonate, complicated changes occur which result in the formation of a substance commonly called yellow prussiate of potash, which has the formula K4FeC6N6. When this substance is heated with potassium, potassium cyanide is formed:
K4FeC6N6 + 2 K = 6KCN + Fe.
Since sodium is much cheaper than potassium it is often used in place of it:
K4FeC6N6 + 2Na = 4KCN + 2NaCN + Fe.
The mixture of cyanides so resulting serves most of the purposes of the pure salt. It is used very extensively in several metallurgical processes, particularly in the extraction of gold. Potassium cyanide is a white solid characterized by its poisonous properties, and must be used with extreme caution.
Potassium carbonate (potash) (K2CO3). This compound occurs in wood ashes in small quantities. It cannot be prepared by the Solvay process, since the acid carbonate is quite soluble in water, but is made by the Le Blanc process. Its chief use is in the manufacture of other potassium salts.
Other salts of potassium. Among the other salts of potassium frequently met with are the sulphate (K2SO4), the acid carbonate (KHCO3), the acid sulphate (KHSO4), and the acid sulphite (KHSO3). These are all white solids.
LITHIUM, RUBIDIUM, CÆSIUM
Of the three remaining elements of the family—lithium, rubidium, and cæsium—lithium is by far the most common, the other two being very rare. Lithium chloride and carbonate are not infrequently found in natural mineral waters, and as these substances are supposed to increase the medicinal value of the water, they are very often added to artificial mineral waters in small quantities.