CHLORIDES. 295 



740. PREPARATION. Chlorides may be 



How are chlo- , , . . ., , , . , 



rides made made by the action of chlorine or hydro- 



chloric acid on the metals. The combus- 

 tion of antimony in chlorine gas, the solu- 

 tion of gold in aqua regia, and that of zinc in hydro- 

 chloric acid are examples. The chemical action in each 

 of these cases has been explained in previous chapters. 

 The solutions being evaporated, the chlorides are ob- 

 tained in the solid form. The solution of zinc in hy- 

 drochloric acid is a case of single elective affinity: 

 the metal elects or chooses the chlorine. 



741. Chlorides may also be formed by 



How are chlo- 



rides produced the action of hydrochloric acid on oxides. 

 from oxide*? Thug common salt or chloride of sodium 



may be made by mixing hydrochloric acid and soda. 

 The hydrogen of the acid and the oxygen of the soda 

 unite to form water, while the chlorine of the acid and 

 the metal sodium unite, to form the chloride. This is 

 a case of double decomposition, resulting from double 

 elective affinity. The chloride commonly corresponds 

 to the oxide from which it is produced. Thus soda, 

 which is a protoxide, yields common salt, which is a 

 protochloride. Again, sesquioxide of iron, containing 

 three atoms of oxygen to one of metal, yields susqui- 

 chloride of iron containing the same proportion of chlo- 

 rine. 



How are the ^2. The insoluble chlorides may be ob- 

 insolubie chlo- tained directly in a solid form by a similar 



rides obtained 



directly in a, double decomposition. Thus, chloride of 

 solid form? so dium and oxide of silver in solution, 



