xvin THE CLASSIFICATION OF THE ELEMENTS 451 



(2) Inflammable or aridiferous element 's, not metallic, 

 hydrogen, nitrogen, sulphur, phosphorus, carbon, and boron 

 (prepared in a crude state from boric anhydride in 1807), 



(3) Metals, 38 in number, as contrasted with Lavoisier's 

 17, including sodium and potassium, barium, strontium, 

 calcium and magnesium; also "aluminum" and "silicum," 

 which Davy had prepared in an impure condition from 

 alumina and silica ( Works, IV. 165-346). 



Elements classified as metals and non-metals. In 

 Lavoisier's system oxygen occupied a unique position as 

 a supporter of combustion for metals and non-metals 

 alike. Davy was fully justified in putting chlorine in the 

 same class, but Gay-Lussac showed in 1814 (p. 246) that 

 chlorine could not stand alone, since sulphur, chlorine and 

 iodine agreed together in their power of uniting both with 

 hydrogen to form hydracids and with oxygen to form oxy- 

 acids. Berzelius in 1825 grouped together under the name 

 of halogens (p. 247) the three elements chlorine, iodine and 

 fluorine (to which bromine was added in 1826), which 

 united directly with metals to form binary haloid-salts ; on 

 the other hand, he grouped together oxygen, sulphur and 

 selenium, all of which could unite with metals and with 

 non-metals to form ternary amphi-salts (p. 248). 



After undergoing so many modifications, the attempt to 

 classify the non-metals as " combustibles " and " supporters 

 of combustion" broke down. Later writers were content 

 to distinguish broadly between METALS and NON-METALS, 

 doubtful elements being described sometimes as METALLOIDS. 

 There is not much difficulty in classifying the elements 

 themselves as metals and non-metals, but confusion and 

 difficulty arise when attempts are made to effect an identical 

 classification by studying the basic or acid qualities of the 

 oxides, or the properties of the chlorides and other com- 

 pounds of the elements. 



G G 2 



