CHAPTER XII 

 CHLORINE. CALCULATIONS 



CHLORINE was discovered by Scheele (1774). It was supposed 

 to be a compound containing oxygen, until the contrary was 

 proved by Davy (1809-1818). It is used in immense quantities 

 for making bleaching and disinfecting agents, explosives and 

 dyestuffs. For its use in gas warfare, see Chapter XL. 



Occurrence. Many compounds of chlorine occur in nature, 

 but the most plentiful is common salt (NaCl) . Most of the mat- 

 ter dissolved in sea water is sodium chloride. Salt also occurs 

 underground, either in strata in almost pure form, or mixed with 

 rocky material. Near such deposits, wells and springs of salt 

 water are common. 



Preparation by Electrolysis of a Chloride. Chlorine is 

 liberated by passing a current of electricity through .a concen- 

 trated aqueous solution of a chloride, such as hydrogen chloride 

 or sodium chloride (see Fig. 27, p. 54). Much of it is, in fact, 

 manufactured by electrolyzing natural brines. The chlorine is 

 liberated, first in solution and later as a gas, at the positive wire 

 (anode). 



Other Products of Electrolysis of Chlorides. In elec- 

 trolyzing hydrochloric acid, the hydrogen is set free at the nega- 

 tive wire (cathode) . With a solution of sodium chloride we might 

 expect to get free sodium at this wire. It will be recalled, however, 

 that sodium is very much more active than is hydrogen, and 

 indeed displaces hydrogen from water. Hence the electrical 

 energy sets free the more easily liberated element the hydrogen 



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