280 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



been expected, proved to be muriate of soda" (A.C.R. 

 VI. 25). 



Common salt was thus shown to be a binary compound 

 of sodium and chlorine, a fact which is expressed by the 

 name SODIUM CHLORIDE. 



Sodium, like potassium, combined with non-metals such 

 as sulphur and phosphorus, formed alloys with tin and other 

 metals, and a solid amalgam with mercury. 



The bases of potash and soda are metals." Should the 

 bases of potash and soda be called metals ? " This question 

 Davy answered in the affirmative. u They agree with metals 

 in opacity, lustre, malleability, conducting powers as to heat 

 and electricity, and in their qualities of chemical combination. 

 Their low specific gravity does not appear a sufficient reason 

 for making them a new class ; for amongst the metals them- 

 selves there are remarkable differences in this respect, 

 platina being nearly four times as heavy as tellurium." 

 Davy therefore decided " to adopt the termination which 

 by common consent has been applied to other newly- 

 discovered metals," and to call the new substances 

 potassium and sodium. He added, "Whatever future 

 changes may take place in theory, there seems, however, 

 every reason to believe that the metallic bases of the 

 alkalies, and the common metals, will stand in the same 

 arrangement of substances ; and as yet we have no good 

 reasons for assuming the compound nature of this class of 

 bodies" (A.C.R. VI. 3335). 



Davy (1808) separates new metals from the alkaline 

 earths. Although the nature of the caustic alkalies had 

 scarcely even been conjectured l before their decomposition 

 by Davy, the similarity between the alkaline earths, such as 

 lime and baryta, and the metallic oxides, had long been 



1 Lavoisier, in 1789, regarded the alkalis as "evidently compound, 

 although we are still ignorant of the nature of the principles which 

 enter into their composition" (Works, I. 137). 



