372 SMITH'S INTERMEDIATE CHEMISTRY 



Its properties are much like those of sodium hydroxide. It is 

 used in making soft soap and other compounds of potassium. 



Potassium Nitrate KHQ. The supply of the natural nitrate 

 being insufficient, the salt is made by double decomposition from 

 the Chile saltpeter NaNO 3 : 



NaNO 3 + KC1 ^KN0 3 + Nad J, . 



Sodium chloride is not much more soluble in hot water than in 

 cold. The three other salts, however, become very soluble as the 

 temperature rises. Hence, when sodium nitrate and potassium 

 chloride are heated with very little water, they dissolve, sodium 

 chloride is precipitated, and potassium nitrate remains in solution. 

 The mass is filtered quickly through canvas to separate the pre- 

 cipitate, and potassium nitrate crystallizes from the filtrate as it 

 cools. 



The salt is used in making gunpowder and fireworks. It is 

 employed also in preserving ham and corned beef. 



Gunpowder. Gunpowder is composed of potassium nitrate 

 (75 per cent), charcoal (15 per cent) and sulphur (10 per cent). 

 The ingredients are moistened with water, and intimately mixed 

 by grinding uftder the heavy rollers of a mill. The " mill cake " 

 is then broken up and granulated to the required size. 



The explosion results largely from the union of the charcoal with 

 the oxygen from the nitrate and of the sulphur with the potassium. 

 One gram of powder yields 264 c.c. of gas (C0 2 , CO, and N 2 ) 

 measured at and 760 mm., and a much larger volume at the 

 temperature of the explosion. One gram produces about 660 

 calories of heat. The explosion is due to the suddenness with 

 which the gases are generated and the heat is developed. The 

 smoke is composed of particles of solid compounds of potassium 

 and is therefore very slow in dissipating itself. Smokeless powder 

 (p. 483) produces no solids when it explodes. 



