(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 when heated, so that these hydrides are distinguished for their considerable stability under heat, but they oxidise very easily.
Thus the analogies and correlation of the metals of these two groups are now clearly marked, not only in their behaviour towards