258 METALS AND THEIR COMBINATIONS. 



Potassium nitrate, Potassii nitras, KNO 3 = 100.43 (Niter, Salt- 

 peter). Potassium and sodium nitrate are found as an incrustation upon 

 and throughout the soil of certain localities in dry and hot countries, 

 as, for instance, in Peru, Chile, and India. The formation of these 

 nitrates is to be explained by the absorption of ammonia by the soil, 

 where it gradually is oxidized and converted into nitric acid. This 

 nitrification, i.4. 9 the conversion of ammonia into nitric acid, seems to 

 be due largely to the action of micro-organisms, termed the nitrifying 

 ferment. The acid after being formed combines with the strongest 

 base present in the soil. If this base be potash, potassium nitrate 

 will be formed ; if soda, sodium nitrate ; if lime, calcium nitrate. 



Upon the same principle is based the manufacture of niter on a large scale, 

 which is accomplished by mixing animal refuse matter with earth and lime, 

 and placing the mixture in heaps under a roof to prevent lixiviation by rain. 

 By decomposition (putrefaction) of the animal matter ammonia is formed, 

 Which, by oxidation, is converted into nitric acid, which then combines with 

 the calcium of the lime, forming calcium nitrate. This is dissolved in water, 

 and to the solution potassium carbonate (or chloride) is added, when calcium 

 carbonate (or chloride) and potassium nitrate are formed : 



Ca(N0 3 ) 2 + K 2 CO 3 == 2KN0 3 + CaCO,. 



Large quantities of potassium nitrate are made also by mixing hot concen- 

 trated solutions of sodium nitrate and potassium chloride, when, on cooling, 

 potassium nitrate separates in crystals, because it is much less soluble in cold 

 water than sodium nitrate is. (See page 193.) 



NaNO 3 + KC1 = KNO 3 + NaCl. 



Potassium nitrate crystallizes in six-sided prisms ; it is soluble in 

 about 3.8 parts of cold, and 0.4 part of boiling water. It has a cool- 

 ing, saline, and pungent taste, and a neutral reaction. When heated 

 with deoxidizing agents or combustible substances, these are readily 

 oxidized. 



It is this oxidizing power which is made use of in the manufacture 

 of gunpowder an intimate mixture of potassium nitrate, sulphur, 

 and carbon. Upon heating or igniting the gunpowder, the sulphur 

 and carbon are oxidized, a considerable quantity of various gases 

 (CO, CO 2 , N, SO 2 , etc.) being formed, the sudden generation and 

 expansion of which cause the explosion. 



Potassium chlorate, Potassii chloras, KC1O 3 =121.68 (Chlorate 

 of potash). This salt may be obtained by the action of chlorine on a 

 boiling solution of potassium hydroxidej as explained on page 237. 



A cheaper process for its manufacture is the action of chlorine 



