100 NON-METALS AND THEIR COMBINATIONS. 



univalent elements, they combine with hydrogen, forming the 

 acids HF1, HC1, HBr, HI; they combine directly with most 

 metals, forming fluorides, chlorides, bromides, and iodides. The 

 relative combining energy lessens as the atomic weight increases ; 

 fluorine with the lowest atomic weight having the greatest, 

 iodine with the highest atomic weight the smallest, affinity for 

 other elements. The first two members of the group are gases, 

 the third (bromine) is a liquid, the last (iodine) a solid at ordi- 

 nary temperature. They all show a distinct color in the 

 gaseous state, have a disagreeable odor, and possess disinfecting 

 properties. 



Occurrence in nature. Chlorine is chiefly found as sodium 

 chloride or common salt, NaCl, either dissolved in water (small 

 quantities in almost every spring water, larger quantities in 

 some mineral waters, and the principal amount in sea-water), 

 or as solid deposits in the interior of the earth. 



Other chlorides, such as those of potassium, magnesium, cal- 

 cium, are also found in nature. As common salt, chlorine 

 enters the animal system, taking there an active part in many 

 of the physiological and chemical changes. 



Preparation of chlorine. Most methods of liberating chlorine 

 depend on an oxidation of the hydrogen of hydrochloric acid by 

 suitable oxidizing agents, the hydrogen being converted into 

 water, whilst chlorine is set free. 



As oxidizing agents, may be used potassium chlorate, potas- 

 sium bichromate, potassium permanganate, chromic acid, nitric 

 acid, and many other substances. 



The most common and cheapest mode of obtaining chlorine 

 is to heat manganese dioxide, usually called black oxide of 

 manganese, with hydrochloric acid, or a mixture of manganese 

 dioxide and sodium chloride with sulphuric acid : 



MnO 2 + 4HC1 = MnCl 2 + 2H 2 O + 2C1. 



Chlorine is also liberated by the action of acids on bleaching- 

 powder, which is a mixture of calcium chloride and calcium 

 hypochlorite : 



CaCl 2 .Ca2C10 -f 2H 2 S0 4 = 2CaSO 4 + 2PI 2 + 4C1. 



