Chemical and Physical Properties of Elements. 33 



oxygen, including the iron-copper group, the platinoid groups, 

 and all the noble and semi-noble metals. Thus the easily oxi- 

 dizable metals are those which have their atoms exposed at 

 large intervals; the semi-noble metals those which have atoms 

 of medium weight at small intervals; and the noble metals 

 those which have heavy atoms at small intervals. The last 

 may be compared to a Macedonian phalanx of large men with 

 shields interlocked; the semi-noble metals to a phalanx of 

 smaller men; and the alkali and alkaline-earth metals to com- 

 panies of small men in skirmishing order. The melting-points 

 of the elements are no less closely associated with the periodic 

 variations of chemical properties than are the atomic volumes. 

 A glance at the line of melting-points (at the top of the figure) 

 shows the closeness of the connexion. The alkali metals have 

 in every case low melting-points ; the alkaline-earth metals 

 melt at considerably higher temperatures ; and the melting- 

 point rises still higher in the metals of the earths, until it cul- 

 minates in those metals which occupy the intermediate posi- 

 tion in the cycle and have low atomic volumes. High melt- 

 ing-point, however, is not always associated with low atomic 

 volume ; and it is curious how, in the second, third, fourth, 

 and fifth cycles, the curve of melting-points, after attaining 

 its maximum in silicon in the iron group and in the two groups 

 of the platinoid metals, suddenly falls, until the melting-point 

 again becomes very low, the minimum being within the region 

 of moderately low volume (about 15). This depression is suc- 

 ceeded by a moderate rise; and then the melting-point falls to 

 the alkali-metal standard. 



The low melting-point of gallium has been considered to be 

 one of the facts which could not have been anticipated by the 

 light of Mendelejeff's conception; and the Kussian chemist, 

 who apparently occupied himself more systematically with 

 chemical than with physical considerations, does not seem to 

 have assigned a low melting-point to ekaluminium, although 

 he has subsequently somewhat empirically attempted to assi- 

 milate the fact into his system. But gallium, in having a low 

 melting-point accords perfectly with its atomic weight and 

 density and properties in general ; it occupies, in fact, the 

 minimum that immediately succeeds the maximum of melting- 

 point, and is analogous to (nitrogen) phosphorus, indium, 

 and mercury in this respect. 



The magnetic properties of the elements have been shown 

 by Carnelley to follow the periodic variations (Chem. News, 

 vol. xl. no. 1038); and he has stated the law in the following 

 manner : — " Those elements belonging to the even series of 

 Mendelejeff's classification are always paramagnetic, whereas 



Phil. Mag. S. 5. Vol. 13. No. 78.' Jan. 1882. D 



