CHAPTER XV. 



CHLORINE, BROMINE AND IODINE. 



CHLORINE is a greenish yellow gas, never found free in nature, 

 but existing in great quantities as an ingredient of common salt. 

 It also occurs in combination with potassium, magnesium and 

 silver. Its formula is Cl and combining weight 35.5. If common 

 salt be mixed with sulphuric acid and heated, a transparent in- 

 tensely acid gas will be given off, which must be collected over 

 mercury, as water absorbs it greedily. The sodium of the com- 

 mon salt and hydrogen of the sulphuric acid change places and 

 the acid is formed, which, dissolved in water, is the hydrochloric 

 acid of commerce. The equation is common salt, 2NaCl-KH 2 S0 4 

 =Na 2 S0 4 , sodium sulphate, -+-2HC1, hydrochloric acid. 



This acid is one of the most useful agents in the chemical labor- 

 atory, and is extensively used in manufacturing industries. As 

 an acid it forms the class of salts called chlorides, as sodium chlo- 

 ride, or common salt. A mixture of hydrochloric and nitric acids, 

 called aqua regia, is the only solvent for gold, the acids decom- 

 pose each other, and the chlorine, when set free, attacks the gold. 



If hydrochloric acid be well mixed with the binoxide of man- 

 ganese, and the mixture heated gradually, chlorine gas will be 

 set free. As it is heavier than air it may be collected in an open 

 jar by carrying a delivery tube to the bottom of the jar, its 

 color enabling one to see when it has filled the jar. The equa- 

 tion is, Mn0 2 +4HCl=MNCl 2 -f 2H 2 0+2C1. Chlorine is usually pre- 

 pared by heating a mixture of common salt, oxide of manganese 

 and sulphuric acid. 



Chlorine combines readily with many elements and decom- 

 poses many compounds from its strong affinity for hydrogen. 

 If a piece of paper, soaked in oil of turpentine that has been 

 slightly warmed, be dropped into a jar of chlorine there will be 

 (120) 



