CHLORINE. 121 



2. Add solution of mercurous salt (mercurous nitrate) : a white 

 precipitate is produced, which blackens on the addition of ammonia: 



Hg 2 2NO 3 + 2NaCl = 2NaNO 3 + Hg 2 Cl 2 . 



3. Add solution of lead acetate : a white precipitate of lead chloride 

 is formed, which is soluble in hot, or in much cold water, and is, there- 

 fore, not formed in dilute solutions. 



4. To a dry chloride add strong sulphuric acid and heat : hydro- 

 chloric acid gas is evolved, which may be recognized by the odor, or 

 by its action on silver nitrate. 



5. Chlorides treated with sulphuric acid and manganese dioxide 

 evolve chlorine. 



Nitre-hydrochloric acid, Aqua reg-ia (Nitro-muriatic add). Ob- 

 tained by mixing 40 c.c. of nitric acid with 180 c.c. of hydrochloric 

 acid. The two acids act chemically upon each other, forming 

 chloronitrous or chloronitric gas, chlorine, and water : 



HNO 3 + 3HC1 = NOC1 + 2H 2 O -f 2C1 , 

 HNO 3 + 3HC1 = NOC1 2 + 2H 2 O + Cl. 



The dissolving power of this acid upon gold and platinum depends 

 on the action of the free chlorine and the action of the chloronitrous 

 and chloronitric gases, both of which part easily with their chlorine. 



The official diluted nitro-hydrochloric add is made by mixing the acids in the 

 quantities above mentioned and adding, when effervescence has ceased, 780 c.c. 

 of water. 



Compounds of chlorine with oxygen. There is no method 

 known by which to combine chlorine and oxygen directly, all the 

 compounds formed by the union of these elements being obtained by 

 indirect processes. The oxides of chlorine are the following : 



Chlorine monoxide or hypochlorous oxide, C1 2 O. 

 Chlorine trioxide or chlorous oxide, C1 2 O 3 . 



Chlorine dioxide, C1O 2 - 



All these oxides are yellow or greenish-yellow gases ; the first and 

 second combine with water, forming the hypochlorous and chlorous 



acids : 



C1 2 O + H 2 O = 2HC1O. 

 C1 2 3 + H 2 = 2HC1O 2 . 



The oxides C1 2 O 5 and C1 2 O 7 from which chloric acid, HC1O 3 , and 

 perchloric acid, HC1O 4 , might be formed, are not known. The chlo- 

 rine oxides, the acids, and many of their salts are distinguished by 

 the great facility with which they decompose, frequently with violent 



