620 PEINCIPLES OF CHEMISTRY 



at a red heat, but gaseous hydrochloric acid is decomposed by it when 

 slightly heated, with evolution of hydrogen and development of a con- 

 siderable amount of heat. Even dilute hydrochloric acid acts in the 

 same manner at the ordinary temperature. Beryllium also acts easily 

 on sulphuric acid, but it is remarkable that neither dilute nor strong 

 nitric acid acts on beryllium, which seems especially able to resist 

 oxidising agents. Potassium hydroxide acts on beryllium as on 

 aluminium, hydrogen beiog disengaged and the metal dissolved, but 

 ammonia has no action on it. These properties of metallic beryllium 

 seem to isolate it from the series of the other metals described in this 

 chapter, but if we compare the properties of calcium, magnesium, and 

 beryllium we shall see that magnesium occupies a position intermediate 

 between the other two. Whilst calcium decomposes water with great 

 ease, magnesium does so with difficulty, and beryllium not at all. The 

 peculiarities of beryllium among the metals of the alkaline earths recall 

 the fact that in the series of the halogens we saw that fluorine differed 

 from the other halogens in many of its properties and had the smallest 

 atomic weight. The same is the case with regard to beryllium among 

 the other metals of the alkaline earths. 



In addition to the above characteristics of the compounds of "the 

 metals of the alkaline earths, we must add that they, like the 

 alkali metals, combine with nitrogen and hydrogen, and while sodium 

 nitride (obtained by igniting the amide of sodium, Chapter XII., 

 Note 44 bis) and lithium nitride (obtained by heating lithium in nitrogen, 

 Chapter XIII., Note 39) have the composition . R 3 N, so the nitrides 

 of magnesium (Note 14), calcium, strontium, and barium, have the 

 composition R 3 N 2 , for example, Ba 3 N 2 , as might be expected from the 

 diatomicityof the metals of the alkaline earths and from the relation of 

 the nitrides to ammonia, which is obtained from all of these compounds 

 by the action of water. The nitrides of Ca, Sr, and Ba are formed 

 directly (Maquenne, 1892) by heating the metals in nitrogen. They all 

 have the appearance of an amorphous powder of dark colour ; as 

 regards their reactions, it is known that besides disengaging ammonia 

 with water, they form cyanides when heated with carbonic oxide ; for 

 instance, Ba 3 N 2 + 2CO = Ba(CN) 2 + 2BaO. 61 



The metals of the alkaline earths, just like Na and K, absorb 

 hydrogen under certain conditions, and form pulverulent easily oxidis- 

 able metallic hydrides, whose composition corresponds exactly to that 

 of 3S"a 2 H and K 2 H, with the substitution of K 2 and Na 2 by the atoms 



61 Thus in the nitrides of the metals we have substances by means of which we can 

 easily obtain from the nitrogen of the air, not only ammonia, but also with the aid ol 

 CO, by synthesis, a whole series of complex carbon and nitrogen compounds. 



