CHLORINE, BROMINE, IODINE, AND FLUORINE. 159 



ing, to a remarkable degree, and are said to form a natural 

 group; the most important member of this group is chlo- 

 rine. 



209. Occurrence of Chlorine. All common salt is made 

 up of this element and a metal called sodium. Afterward, 

 when you have learned the remarkable properties of the 

 constituents of salt, how one is a suffocating yellow gas, and 

 the other a very light, soft metal which burns on water, it 

 will seem rather strange that a union of these two bodies, 

 both of them so corrosive and dangerous, should produce 

 such a mild, healthful substance as common salt. And yet 

 this is only another example of the marvelous change which 

 elements experience when united, each one losing its iden- 

 tity, and the compound having the properties of neither of 

 them. Chlorine forms more than one half of common salt ; 

 so that, as salt is abundant in sea-water and in salt-mines, 

 and is also present to some extent in the soil and in animals 

 and vegetables, chlorine 



is one of the elements 

 that exists in large quan- 

 tities in the earth. 



210. Preparation of 

 Chlorine. Chlorine is 

 never found free in nat- 

 ure ; we can make it 

 from common salt. Mix 

 some common salt, or 

 chloride of sodium, with 

 manganese dioxide, put 

 the mixture into a flask 

 fitted with a tube, as in ^ 

 Fig. 65, and then add 

 some sulphuric acid 



somewhat diluted. K"ow Fig. G&. 



