LESSONS IN CHEMISTRY. 153 



caustic potash in appearance and quality. It is usually obtained 

 as a by-product in the manufacture of sodium carbonate. It is 

 used in the manufacture of hard soap. Sodium sulphate, Na 2 S0 4 , 

 is a salt called Glauber's salt. It is produced as a by-product in 

 the manufacture of hydrochloric acid. 



Nitrate of soda, or Chili saltpeter, is imported from Peru. It 

 is used as a fertilizer and in the manufacture of potassium ni- 

 trate. Fifteen parts of clean sand fused with eight parts of car- 

 bonate of soda form a silicate of soda, which is soluble in hot 

 water, forming a strongly alkaline solution called soluble glass. 

 It is sometimes used to lessen the inflammability of wood, and 

 sometimes as a matrix in forming some kinds of artificial 

 stone. 



Ammonia, NH 3 , and the hypothetical metal ammonium, NH 4 , 

 have been mentioned ; but several salts of ammonium are inter- 

 esting, and may be considered here as they are somewhat similar 

 to corresponding compounds of sodium and potassium. Am- 

 monium chloride is sometimes found in nature, but is usually 

 prepared from the ammoniacal liquors of gas works. These 

 liquors are treated with hydrochloric acid, the solution evapo- 

 rated and the residue heated, when the ammonium chloride vap- 

 orizes without melting, and is condensed on cold surfaces in a 

 crystalline form. It has a sharp salty taste, and is freely soluble 

 in water, lowering the temperature considerably, so that it is 

 frequently used in making freezing mixtures. From it ammonia 

 and carbonate of ammonia are prepared, and it is used in dye- 

 ing, in soldering copper and brass, and in galvanizing iron. 



Ammonium sulphide (NH 4 ) 2 S,is prepared bypassing hydrogen 

 sulphide through aqua ammonia, 2NH 3 H-H 2 S=(NH 4 ) 2 S. This 

 compound is a colorless liquid of unpleasant odor, which soon 

 becomes yellowish from partial decomposition. It is a very use- 

 ful agent in the laboratory. 



Bicarbonate of ammonia H(NH 4 )C0 3 , called "smelling salts," 

 is frequently used in medicine, and it is also used by bakers and 

 confectioners. Ammonium sulphate, (NH 4 ) 2 S0 4 , is used in the 

 manufacture of artificial manures and ammonium alum. 



