CHLORINE. CALCULATIONS 143 



and chlorine. When the mixture is warmed, the MnCl 3 breaks 

 down further into MnQ 2 and chlorine. The complete series of 

 reactions may be represented in one equation as follows: 



Mn0 2 + 4HC1 - 2H 2 + MnCl 2 + C1 2 . (1) 



If we had used manganous oxide MnO, we should have had a 

 double decomposition: 



MnO + 2HC1 -> H 2 + MnCl 2 , (2) 



but we should have got no chlorine. The difference between 

 these two actions will be discussed in a later chapter (p. 215). 



Physical Properties. Chlorine is a greenish-yellow gas, and 

 takes its name from the Greek for this color. It has an exceedingly 

 disagreeable odor and irritates the lining of the nose and throat. 

 Alcohol vapor or ammonia, when breathed, relieves the irritation. 



The density of the gas is recorded in the formula C1 2 . The 

 22.4-liter-cube-full weighs 70.92 g., against 28.95 g. for air, so 

 that chlorine is about 2j times heavier. Two volumes of the 

 gas dissolve in one volume of water at 20. The solution is called 

 chlorine-water. 



The gas is liquefied by pressure below 146 (its critical tem- 

 perature), the pressure required at 20 being 6.6 atmospheres. 

 The liquid boils at -33, and solidifies at -102 (its melting- 

 point) . 



Chemical Properties. Chlorine is an element with about 

 the same degree of activity as oxygen (compare p. 141), and it 

 unites with very much the same list of other elements. The 

 compounds are called chlorides. 



Unites with Metals. When powdered antimony (cold) or 

 iron powder (warmed) are thrown into chlorine, they combine 

 with it, and red hot particles of the chlorides, SbCl 3 or FeCl 3 , fall 

 to the bottom. Copper leaf (Dutch metal, used in " gilding "), 



