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LXIV. On the Natural Groupings of the Elements. By Wil- 

 liam Odling, M.B. Lond., Professor of Practical Chemistry 

 at Guy's Hospital; Sea'etaru to the Chemical Society*. 



Part II. 



IN the former part of tins communication I discussed the cor- 

 relations of the principal chlorous elements, proceeding 

 from the most chlorous downwards. I propose now to com- 

 mence at the other extremity of the scale, and in considering the 

 purely metallic groups, to proceed in the order of their basylous 

 characters. 



Group V. Lithium, Sodium, Potassium. 



The mutual resemblance of these three metals is admitted on 

 all hands. Their chief points of association are the following. 

 Their atomic weights occur in sequence, that of sodium being 

 the mean of the three : — 



Lithium . . 6*5 68*5 _ „« o 



Sodium . . 23-0 -g--w5^-» 



Potassium . . 39-0 



Sum . . . 68-5 Mean difference = 16. 



The three metals are soft, fusible, volatile, and of low specific 

 gravity; they decompose water at all temperatures, and are 

 readily combustible. Each metal forms only one class of salts. 

 Nearly all the salts are soluble in water, and undecomposed by 

 heat. Corresponding potassium, sodium, and probably lithium 

 salts are isodimorphous ; but the isomorphism of the group is 

 not striking, inasmuch as the con-cspondiug salts frequently 

 crystallize with different ^proportions of water of crystallization. 

 Very many of the salts present gradatioiial properties : thus the 

 carbonate of lithium is very sparingly soluble in water, that of 

 sodium moderately soluble, that of potassium extremely soluble. 



The specific gravities of the three metals, Li = 0*593, Na=0"972, 

 and K = 0"865, are not sequential. The atomic volume of sodium 

 approximates to the mean of the three. Thus — 



Li = 136 993__„- 

 Na = 295 -3- -^"^^ 

 K = 562 



Sum 993 



* Communicated bv the Author. 



