368 



SCIENTIFIC RECREATIONS. 



detected in the strong smell of seaweed. Its combinations with metals are 

 termed bromides. It is a powerful poison. 



IODINE is another relative of chlorine. It is found in seaweed, which 

 by burning is reduced to kelp. When iodine is heated a beautiful violet 

 vapour comes off, and this characteristic has given it its name ("iodes," violet). 

 Iodine was discovered by Courtois, of Paris, and in 1813, Gay Lu ssac made it 

 a special study. It is solid at ordinary temperatures, and assumes 

 crystallized forms in plates of metallic lustre. It is an excellent remedy in 

 "goitre" and such affections. (Symbol I. Atomic weight 127.). 



FLUORINE is very difficult to prepare. Fluor spar is a compound of 

 fluorine and calcium. This element is gaseous, and combines so rapidly 

 that it is very difficult to obtain in a free state. Etching on glass is accom- 



Fig. 363. Apparatus for obtaining dry chlorine gas. 



plished by means of hydrofluoric acid, for fluorine has a great affinity for 

 silicic acid, which is contained in glass. The glass is covered with wax, 

 and the design is traced with a needle. The acid attacks the glass and 

 leaves the wax, so the design is eaten in. (Symbol F. Atomic weight 19.) 



Chlorine, fluorine, bromine, and iodine are termed " Halogens " 

 (producers of salts). They appear, as we have seen, in a gaseous, liquid, and 

 solid form respectively. 



CARBON is the most, or one of the most, largely diffused elements in 

 nature, and claims more than a passing notice at our hands, though ever*, 

 that must be brief. We may put down carbon next to oxygen as the most 

 important element in the world. The forms assumed by carbon arc very 

 variable, and pervade nature in all its phases. We have carbon in crystals,. 



