POTASSIUM, RUBIDIUM, CESIUM, AND LITHIUM 577 



they bear to each other. The isolated metals, 42 rubidium and caesium, 

 have respectively the specific gravities 1*52 and 2*366, and melting 

 points 39 b and 27 as N.N. Beketoff showed (1894), he having obtained 

 csesium by heating GsA10 2 with Mg ( 42 bls ). 



Judging by the properties of the free metals, and of their corre- 

 sponding and even very complex compounds, lithium, sodium, potas- 

 sium, rubidium, and caesium present an indubitable chemical resem- 

 blance. The fact that the metals easily decompose water, and that their 



42 Bunsen obtained rubidium by distilling a mixture of the tartrate with soot, and 

 Beketoff (188B) by heating the hydroxide with aluminium, 2RbHO + Al = RbA10 2 + H 2 + Rb. 

 By the action of 85 grams of rubidium on water, 94,000 heat units are evolved. Setterberg 

 obtained caesium (1882) by the electrolysis of a fused mixture of cyanide of caesium and 

 of barium. Winkler (1890) showed that metallic magnesium reduces the hydrates and 

 carbonates of Rb and Cs like the other alkaline metals. N. N. Beketoff obtained them 

 with aluminium (see following note). 



42 bla Beketoff (1888) showed that metallic aluminium reduces the hydrates of the 

 alkaline metals at a red heat (they should be perfectly dry) with the formation of 

 aluminates (Chapter XVII.), RA1O 2 for example, 2KHO + Al = KAlO 2 + K-f H 2 . Ifc is 

 evident that in this case only half of the alkaline metal is obtained free. On the other 

 hand, K. Winkler (1889) showed that magnesium powder is also able to reduce the 

 alkaline metals from their hydrates and carbonates. N. N. Beketoff and Tscherbacheff 

 (1894) prepared caesium upon this principle by heating its aluminate CsAlO 2 vriih 

 magnesium, powder. In this case aluminate of magnesium is formed, and the whole of 

 the caesium is obtained as metal: 2C8A10 2 + Mg = MgOAl 2 O 3 + 2C8. A certain excess of 

 alumina was taken (in order to obtain a less hygroscopic mass of aluminate), and 

 magnesium powder (in order to decompose the last traces of water) ; the CsA10 2 was 

 prepared by the precipitation of caesium -alums by caustic baryta, and evaporating the 

 resultant solution. We may add that N. N. Beketoff (1887) pr'epared oxide of potassium, 

 K 2 O, by heating the peroxide, KO, in the vapour of potassium (disengaged from its alloy 

 with silver), and showed that in dissolving in an excess of water it evolves (for the above- 

 given molecular weight) 67,400 calories (while 2KHO in dissolving in water evolve? 

 24,920 cal. ; so that K 2 O + H 2 O gives 42,480 cal.), whence (knowing that K 3 + O + H 2 O in 

 an excess of water evolves 164,500) it follows that K 2 + O evolves 97,100 cal. This quantity 

 is somewhat less than that (100,260 cal.) which corresponds to sodium, and the energy of 

 the action of potassium upon water is explained by the fact that K 2 O evolves more heat 

 than Na^O in combining with water (see Chapter II. Note 9). Just as hydrogen displaces 

 half the Na from Na-jO forming NaHO, so also N. N. Beketoff found from experiment 

 and thermo-chemical reasonings that hydrogen-displaces half the potassium from K 2 O, 

 forming KHO and evolving 7,190 calories. Oxide of lithium, Li 2 O, which is easily 

 formed by igniting Li 2 CO 3 with carbon (when Li 2 O + 2CO is formed), disengages 

 26,000 cals. with an excess of water, while the, reaction Li 2 + O gives 114,000 cals. and 

 the reaction Li 2 + H 2 O gives only 13,000 cals., and metallic lithium cannot be liberated 

 from oxide of lithium with hydrogen (nor with carbon). Thus in the series Li, Na, K, 

 the formation of R-jO gives most heat with Li and least with K, while the formation of 

 RC1 evolves most heat with K (105,000 cals.) and least of all with Li (98,500 cals.). 

 Rubidium, in forming Rb 2 O, gives 94,000 'cals. (Beketoff). Caesium, in acting upon an 

 excess of water, evolves 51,500 cals., and the reaction Cs 2 + O evolves about 100,000 cals. 

 i.e. more than K and Rb, and almost as much as Na and oxide of caesium reacts 

 with hydrogen (according to the equation Cs 2 O + H = CsHO + Cs) more easily than any 

 of the oxides of the alkali metals, and this reaction takes place at the ordinary tem- 

 perature (the hydrogen is absorbed), as Beketoff showed (1893). He also obtained a 

 mixed oxide, AgCsO, which was easily formed in the presence of silver, and absorbed 

 hydrogen with the formation of CsHO. 



