POTASSIUM, RUBIDIUM, CAESJt .M. AND LITHIUM 571 



The atomic weights of the alkali metals, lithium 7, sodium 23, po- 

 tassium 39, rubidium 85, and caesium 133, show that here, as in the 

 halogens, the elements may be arranged according to their atomic 

 weights in order to compare the properties of the analogous compounds 

 of the members of this group. Thus, for example, the platinochlorides 

 of lithium and sodium are soluble in water ; those of potassium, 

 rubidium, and caesium sparingly soluble, and the greater the atomic 

 weight of the metal the less soluble is the salt. In other cases the 

 reverse is observed the greater the atomic weight the more soluble 

 are the corresponding salts. The variation of properties with the varia- 

 tion in atomic weights even shows itself in the metals themselves ; thus 

 lithium volatilises with difficulty, whilst sodium is obtained by means 

 of distillation, potassium volatilises more easily than sodium, and rubi- 

 dium and caesium, as we have seen, are still more volatile. 



Schiitzenberger obtained a compound C 2 H 3 O(OC1), which he called chlorine acetate, by 

 acting on acetic anhydride, (C^HjOJoO, with chlorine monoxide, CloO. With iodine this 

 compound disengages chlorine and forms iodine acetate, C 2 H 3 O(OI), which also is formed 

 by the action of iodine chloride on sodium acetate, C. 2 H 5 O(ONa). Such compounds are 

 very unstable, decompose with an explosion when heated, and are changed by the action 

 of water and of many other re-agents, which is in accordance with the fact that they con- 

 tain very closely-allied elements, as CloO itself, or IC1 or KNa. By the action of chlorine 

 monoxide on a mixture of iodine and acetic anhydride, Schiitzenberger also obtained the 

 compound ^C^H^O^o, which is analogous to IC^, because the group CgHjOo is, like Cl, 

 a halogen, forming salts with the metals. 



