ATOMIC THEOKY. 



41 



atomic weights. Lothar Meyer has constructed 

 a graphic representation exhibiting the rela- 

 tion of the physical properties of the elements 

 to their atomic weights and volumes. The 

 elements are arranged at distances from the 

 origin along the axis of abscissae proportional 

 to their atomic weights. The ordinates of the 

 curve indicate their atomic volumes, and the 

 curve the variations of these in their successive 

 order. From the portions of this curve which 

 have been determined, it appears that it repre- 

 sents also variations in the above-mentioned' 

 physical properties. It is seen that the posi- 

 tion of the elements on the ascending or de- 

 scending portions of the curve determines their 

 properties, which may thus be very different 

 for bodies possessing nearly the same atomic 

 weight, and yet harmonize in a remarkable 

 manner with the other terms of the theory. 

 The light metals which occupy the summits 

 and contiguous descending parts of the curve 

 are ductile ; and the heavy metals at the bottom 

 and lower part of the ascending curve are par- 

 tially ductile. In the fourth group the ductil- 

 ity is seen to increase and diminish twice in one 

 period of the variations of density. Fusibil- 

 ity and conductivity, with increasing atomic 

 weights, exhibit the same principle of variabil- 

 ity. Crystalline form and expansibility by 



heat are found also to depend upon atomic 

 weight, according to the same law of perio- 

 dicity. Fizeau's experiments have proved that 

 the co-efficient of expansion rises and sinks reg- 

 ularly as the atomic weight increases. Du- 

 long's law of relativity between atomic weights 

 and specific heats, probably for lack of exact 

 measurements, can only be determined in cases 

 where atomic weights and atomic volume are 

 both low. Dulong's law is not periodic, the 

 specific heat being uniformly inversely propor- 

 tional to the atomic weight. Lecoq de Bois- 

 baudran has proved that, in the homologous 

 series of elements, the wave-lengths of the lu- 

 minous rays which they emit are proportional 

 to their atomic weights. The electro-chemical 

 character of the elements follows the law of 

 periodic variations, the passage from the elec- 

 tro-positive to the electro-negative character 

 taking place in certain groups twice in the 

 same period of density variation. The elec- 

 tro-chemical condition governs the power of 

 combination, to a certain extent; the stable 

 protoxides, for example, being formed with 

 electro-positive metals, and powerful acids rich 

 in oxygen with electro-negative elements. 

 Electro-negative hydrogen, on the contrary, 

 forms its most stable simple compounds with 

 electro-positive elements. 



