THE VALENCY AND SPECIFIC HEAT OF THE METALS 591 



are one unit less than the former. 9 They all belong to the number of 

 light metals, as they have but a small specific gravity, in which respect 

 they differ from the ordinary, generally knbwn heavy, or ore, metals (for 

 instance, iron, copper, silver, and lead), which are distinguished by a 

 much greater specific gravity. There is no doubt that their low specific 

 gravity has a significance, not only as a simple point of distinction, but 

 also as- a property which determines the fundamental properties of these 

 metals. Indeed,, all thg light metals have a series of points of resem 

 blance with the metals of the alkalis ; thus both magnesium and 

 calcium, like the metals of the alkalis, decompose water (without the 

 addition of acids), although not so easily as the latter metals. The 

 process of the decomposition is essentially one and the same ; for 

 example, Ca 4- 2H 2 O = CaH 2 O 2 + H 2 that is, hydrogen is liberated 

 and a hydroxide of the metal formed. These hydroxides are bases 

 which neutralise nearly all acids. However, the hydroxides RH 2 O 2 of 

 calcium and magnesium are in no respect so energetic as the hydroxides 

 of the true metals of the alkalis ; thus when heated they lose water, 

 are not so soluble, develop less heat with acids, and form various salts, 

 which are less stable and more easily decomposed by heat than the 

 corresponding salts of sodium and potassium. Thus calcium and 

 m.agnesium carbonates easily part with carbonic anhydride when 

 ignited ; the nitrates are also very easily decomposed by heat, calcium 

 and magnesium oxides, CaO and MgO, being left behind. The chlorides 

 of magnesium and calcium, when heated with water, evolve hydrogen 

 chloride, forming the corresponding hydroxides, and when ignited the 

 oxides themselves. All these points are evidence of a weakening of the 

 alkaline properties. 



These metals have been termed the metals of the alkaline earths, 

 because they, like the alkali metals, form energetic bases. They are 

 called alkaline earths because they are met with in nature in a state of 

 combination, forming the insoluble muss of the earth, and because as 

 oxides, RO, they themselves have an earthy appearance. Not a few 

 salts of these metals are known which are insoluble in water, whilst 

 the corresponding salts of the alkali metals are generally soluble for 

 example, the carbonates, phosphates, borates, and other salts of the 

 alkaline earth metals are nearly insoluble. This enables us to separate 

 the metals of the alkaline earths from the metals of the alkalis. For 

 this purpose a solution of ammonium carbonate is added to a mixed 

 solution of salts of both kinds of metals, when by a double decomposition 

 the insoluble carbonates of the metals of the alkaline earths are formed 



As if NaH = Mg and KH = Ca, which is in accordance with their valency. KH 

 includes two monovalent elements, and is a bivalent group like Ca. 



