LESSONS IN CHEMISTRY. 147 



rocks, and these, broken down and pulverized, yield up a 

 portion of their potassium to growing vegetation. When 

 vegetable structures are burned, the potassium forms a por- 

 tion of the ash in the form of a carbonate, formula K 2 C0 3 . 

 When the wood ashes are leached with water the potassium car- 

 bonate is dissolved out and the solution evaporated yields an 

 impure salt, called potash, which is much used in the manufacture 

 of soft soap and of glass. It is also a valuable fertilizer. The 

 hydroxide or caustic potash is obtained from the solution of po- 

 tassium carbonate by treating it with slaked lime. The chemical 

 equation is K 2 C0 3 +CA0 2 H 2 , calcium hydroxide, =CaC0 3 , calcium 

 carbonate +2KOH, the potassium hydroxide. This compound 

 is a brittle, white solid , having a strong affinity for water, so that 

 it rapidly deliquesces in the air. It is the most powerful alkali 

 in use, and its activity as a chemical agent makes it of great 

 value to the chemist. It is used in medicine as a caustic. It re- 

 places the hydrogen of acids forming salts, as the carbonates, 

 nitrates and sulphates. It decomposes animal and vegetable 

 substances, whether living or dead. Potassium bicarbonate, for- 

 mula HKC0 3 ,is a salt much used in medicine for making efferves- 

 cent solutions by adding citric or tartaric acids. 



Another very common and important salt of this metal is 

 potassium nitrate niter, or saltpeter, formula KN0 3 . It is a nat- 

 ural product of some parts of India and is produced in an artifi- 

 cial way, by heaping up organic matter with lime, ashes and 

 soil, keeping the mass well moistened with urine for two or three 

 years. In the mass nitrates are slowly formed and may be 

 leached out with water and purified for use. The potassium 

 nitrate may also be prepared from the sodium nitrate by treating 

 it with potassium chloride, according to the following equation : 

 NaN0 3 , sodium nitrate, +KCL, potassium chloride, KN0 3 

 niter, -hNaCl sodium chloride, all in solution together. In evap- 

 orating this solution the sodium chloride, being less soluble in 

 boiling water, crystallizes out, leaving the niter still in solu- 

 tion. When the solution is allowed to cool the niter crystallizes 

 out, as it is less soluble in cold water, leaving some chlorides 



