608 PRINCIPLES OF CHEMISTRY 



anhydrous oxide gives, as has already been mentioned in Chapters Til.. 

 and IV., a peroxide, BaO 2 . 56 Neither calcium nor strontium oxides 

 are able to give such a peroxide directly, but they form peroxides under 

 the action of hydrogen peroxide. 



Barium oxide is decomposed when heated with potassium ; and fused 

 barium chloride is decomposed, as Davy showed, by the action of a 

 galvanic current, forming metallic barium ; and Crookes (1862) obtained 

 an amalgam of barium from which the mercury could easily be driven 

 off, by heating sodium amalgam in a saturated solution of barium 

 chloride. The same occurs with strontium. Both metals are soluble in. 

 mercury, and seem to be non-volatile or at least very slightly volatile, 

 They are both heavier than water ; the sp. gr. of barium is 3 -6, and of 

 strontium 2 - 5. They both decompose water at the ordinary temperature,, 

 like the metals of the alkalis. 



Barium and strontium as saline elements are characterised by their 

 powerful basic properties, so that they form acid salts with difficulty, 

 and scarcely form basic salts. On comparing them together and with 

 calcium, it is evident that the alkaline properties in this group (as in 

 the group potassium, rubidium, caesium) increase with the atomic 

 weight, and this succession clearly shows itself in many of their corre- 

 sponding compounds. Thus, for instance, the solubility of the 

 hydroxides RH 2 O 2 and the specific gravity 57 rise in passing from 

 calcium to strontium and barium, while the solubility of the sulphates 

 decreases,^ 8 and therefore in the case of magnesium and beryllium as 

 metals whose atomic weights are still less, we should expect the solu- 

 bility of the sulphates to be greater, and this is the case in reality. 



5t > The property of barium oxide of absorbing oxygen when heated, and giving the 

 peroxide BaOo, is very characteristic for this oxide. It is only proper to the anhydrous 

 oxide. The hydroxide does not absorb oxygen. Peroxides of calcium and strontium may 

 be obtained by means of hydrogen peroxide. Barium peroxide is insoluble in water, but 

 is able to form a hydrate with it, and also to combine with hydrogen peroxide, forming a, 

 very unstable compound having the composition BaH 2 O4 (obtained by Professor Schone), 

 and which in the course of time evolves oxygen (Chapter IV. Note 21). 



57 Even in solutions a gradual progression in the increase of the specific gravity shows 

 itself, not only for equivalent solutions (for instance, KC1 2 + 200H 2 O), but even with an 

 equal percentage composition, as is seen from the curves giving the specific gravity 

 (water 4 = 10000) M 15 (for barium chloride, according to Bourdiakoff's determina- 



tions) : 



BeCl 2 : S - 9992 + 6TZlp + O'lllp 2 



CaCl 2 : S = 9992 + 80'24p + 0'476p* 

 SrCl 2 : 8 = 9992 + 85-572? +0-733^ 2 

 BaClo : 



58 One part of calcium sulphate at the ordinary temperature requires about 500 parts 

 of water for solution, strontium sulphate about 7000 parts, barium sulphate about 400000 

 parts, whilst beryllium sulphate is easily soluble in water. 



