THE VALENCY AND SPECIFIC HEAT OF THE METALS 621 



Be, Mg, Ca, Sr, and Ba. The hydrides of the metals of the alkaline 

 earths were discovered by C. Winkler (1891) in investigating the 

 reducibility of these metals by magnesium. In reducing their oxides 

 by heating them with magnesium powder in a stream of hydrogen, 

 Winkler observed that the hydrogen was absorbed (but very slowly), i.e. 

 at the moment of their separation all the metals of the alkaline earths 

 combine with hydrogen. This absorptive power increases in passing 

 from Be to Mg, Ca, Sr, and Ba, and the resultant hydrides retain the 

 combined hydrogen 62 when heated, so that these hydrides are distin- 

 guished for their considerable stability under heat, but they oxidise 

 very easily. 63 



Thus the analogies and correlation of the metals of these two groups 

 are now clearly marked, not only in their behaviour towards oxygen, 

 chlorine, acids, &C M but also in their capability of combining with 

 nitrogen and hydrogen. 



62 As the hydrides of calcium, magnesium, &c. are very stable under the action of 

 heat, and these metals and hydrogen occur in the sun, it is likely that the formation of 

 their hydrides may take place there. (Private communication from Prof. Winkler, 1894.) 

 It is probable that in the free metals of the alkaline earths hitherto obtained a portion" 

 was frequently in combination with nitrogen and hydrogen. 



63 Thus, for instance, a mixture of 56 parts of CaO and 24 parts of magnesium powder 

 is heated in an iron pipe (placed over a row of gas burners as in the combustion furnace 

 used for organic analysis) in a stream of hydrogen. After being heated for hour the 

 mixture is found to absorb hydrogen (it no longer passes over the mixture, but is retained 

 by it). The product, which is light grey, and slightly coherent, disengages a mass of 

 hydrogen when water is poured over it, and burns when heated in air. The resultant 

 mass contains 33 per cent. CaH, about 28 per cent. CaO, and about 38 per cent. MgO. 

 Neither CaH nor any other MH has yet been obtained in a pure state. 



The acetylene derivatives of the metals of the alkaline earths C 2 M (Chapter VIII., 

 Note 12 bis), for instance, C 2 Ba, obtained by Maquenne and Moissan, belong to the same 

 class of analogous compounds. It must here be remarked that the oxides MO of the 

 metals of the alkaline earths, although not reducible by carbon at a furnace heat, yet 

 under the action of the heat attained in electrical furnaces, not only give up their oxygen 

 to carbon (probably partly owing to the action of the current), but also combine with car- 

 bon. The resultant compounds, C 2 M, evolve acetylene, C 2 H 2 , with HC1, just as N 2 M3 

 give ammonia. We may remark moreover that the series of compounds of the metals of 

 the alkaline earths with hydrogen, nitrogen and carbon is a discovery of recent years, and 

 that probably further research will give rise to similar unexpected compounds, and by 

 extending our knowledge of their reactions prove to be of great interest. 



