424 Prof. Odling on the Natural Groupings 



the association, nor availed themselves of it as a means of clas- 

 sification. Oa the contrary, although the groupings of the ele- 

 ments are as real and certain as the natural families of plants and 

 animals, yet we find constantly, in our systematic treatises, that 

 bodies manifesting the strongest analogies are widely separated 

 from one another, while bodies belonging to very different groups 

 are conventionally associated. 



The existence of certain important natural families has been 

 successively pointed out by different chemists. I propose to 

 make some modifications in the groupings hitherto proposed, to 

 construct a few new groups, and to point out the principal ana- 

 logies by which the members of each particular group, old or 

 new, are associated ; relying chiefly upon well-known recorded 

 facts, but occasionally introducing fresh experiments and obser- 

 vations. 



The most prominent relations which obtain among the elements 

 are the relation of parity or equality, and the relation of series 

 or gradation ; but an aliquot or multiple relation is also occasion- 

 ally manifested*. The relation of parity is illustrated in the 

 case of the twin-metals nickel and cobalt, and the relation of 

 series in the triad chlorine, bromine, and iodine. The multiple 

 relation is not shown by any such glaring instance. Some ap- 

 parently multiple relations may indeed be only uncompleted 

 relations of gradation, of which occurrence palladium and plati- 

 num afford a possible example ; while other numerically multiple 

 relations are scarcely supported by analogy of properties, as 

 happens with platinum and gold. Frequently, however, we find 

 that two proportions of one metal are isomorphous with one pro- 

 portion of another, as is the case with copper and silver. 



In attempting a natural classification of the elements, we must 

 have regard, though not an equal regard, to all the properties 

 they manifest ; or in other words, we must be guided by the 

 totality of their characters. If we find that two or more elements 

 form a large number of compounds of analogous composition, 

 and if, moreover, these analogous compounds present a marked 

 similarity of properties, we shall generally be justified in asso- 

 ciating the elements in question, despite the generation by each 

 of compounds to which the other furnishes no analogues. More- 

 over, if we find a marked general accordance in properties, we 

 must overlook a discrepancy in some one particular set of pro- 

 perties, or regard it as pertaining only to the imperfect state of 

 our knowledge. In considering the relation of gradation more 

 especially, we must be cai-eful not to mistake differences in degree 

 for differences in kind. The protosalts of iron and copper show 



* These relations correspond generally with those pointed out by Glad- 

 stone, Phil. Mag. S. 4. May 1853. 



