CARBONATES. 315 



Describe an- 796. Another method of manufacturing 

 other method, carbonate of soda, consists, essentially, 

 in separating sulphur from the sulphate, by means of 

 oxide of iron, and substituting carbon in its place. In 

 this process also, the materials are heated with charcoal, 

 in a reverberatory furnace, and the carbonate afterward 

 extracted by water. The impure uncrystallized carbo- 

 nate of soda, is known in commerce, as soda ash, and 

 is largely employed in the manufacture of hard soap, 

 and in other processes. 



What is sal 797. CARBONATE OF AMMONIA. SAL VOL- 



volatile? ATILE. The ordinary sal volatile of the 



shops, used as smelling salts, is a carbonate containing 

 three equivalents of acid to two of base. It wastes away 

 gradually in the air, and passes off in a gaseous form. 



798. PREPARATION. Sal volatile is pre- 



How is sal . 



volatile pre- pared by heating together carbonate of 

 pared \ime and chloride of ammonium. Carbo- 



nate of ammonia immediately passes off', while chloride 

 of calcium remains behind. The carbonate is led into 

 a cold pipe or chamber, where it takes the solid form. 

 The mixture of chalk and sal ammoniac is sometimes 

 used as smelling salts. The production of sal volatile 

 from the mixture is very gradual if heat is not applied. 



799. The property from which 



How is it 



proved to be the salt receives its name, may 

 volatile f be illustratedj by holding in its 

 vicinity a rod or roll of paper, moistened with 

 strong muriatic acid. A dense cloud of sal 

 ammoniac is immediately produced in the 

 air, from the union of the two vapors. The 



