134 METALS AND THEIR COMBINATIONS. 



tions, which usually may be obtained by fusing the metals together, 

 must be looked upon as molecular mixtures, not as definite chemical 

 compounds. All alloys still exhibit the metallic nature in their 

 general physical characters. It is different, however, when metals 

 combine with non-metals ; in this case the metallic characters are 

 lost almost invariably. 



All metals combine with chlorine, fluorine, and oxygen; most 

 metals also with sulphur, bromine, and iodine, forming the respective 

 chlorides, fluorides, oxides, sulphides, bromides, and iodides. Metals 

 replace hydrogen in acids, forming salts. 

 r Most metals may be obtained from their oxides by heating the 



/latter with charcoal, the carbon combining with the oxygen of the 



/ oxide, whilst the metal is liberated : 



MO + C = CO + M; 

 or 



2MO + C = CO 2 + 2M. 



Also hydrogen may be used in some cases as the deoxidizing agent : 

 MO + 2H = H 2 -f M. 



Some metals are found in nature chiefly as sulphides, which usually 

 are converted into oxides (before the metal can be obtained) by roast- 

 ing. The term roasting, when used in metallurgy, means heating 

 strongly in an oxidizing atmosphere, when the sulphides are con- 

 verted into sulphates or oxides, thus : 



MS + 4O = MSO 4 ; 

 or 



MS + 3O = MO + SO 2 . 



19. POTASSIUM (KALIUM). 



K 1 = 39 (39 03). 



General remarks regarding- alkali-metals. The metals potas- 

 sium, sodium, lithium (rubidium and csesium) form the group of the 



~ 



QUESTIONS. 171. How many metals are known, and about how many are 

 of general interest? 172. Mention some metals having very low and some 

 having very high fusing-points. 173. What range of specific gravities do we 

 find among the metals? 174. Mention some univalent and some bivalent 

 metals ; also some which show a different valence under different conditions. 

 175. Mention some metals which are found in nature in an uncombined state ; 

 some which are found as oxides, sulphides, chlorides, and carbonates, respec- 

 tively. 176. Into what two groups are the metals divided? 177. State the 

 three groups of light metals ? 178. What is a metal ? 179. What is an alloy, 

 and what an amalgam? 180. By what process can most metals be obtained 

 from their oxides ? 



