October 27, 1911] 



SCIENCE 



549 



pressible, because we might infer from 

 their bulk that they are not under as great 

 pressures as the small volumes, and ma- 

 terial under slight pressure is likely to be 

 easily compressible. Moreover, the bulky 

 and easily compressible elements are in 

 most cases more easily melted and volatil- 

 ized than those possessing small volume 

 and slight compressibility. This is just 

 what we might expect ; all these properties 

 combine to indicate that the bulky elements 

 have less cohesion than the compact ones. 



Next, another set of waves may be con- 

 sidered, representing properties not often 

 depicted in this way. These are the heats 

 of formation of sundry similar compounds, 

 also plotted with relation to the atomic 

 weights. In the third curve are given the 

 heats of combination of chlorine with other 

 elements, and below it a heavy line de- 

 picting the heats of the combination of 

 oxygen with these elements, both sets of 

 quantities being expressed in terms of 

 gram-equivalents. 



These two run partly parallel with one 

 another ; but a deviation in the parallelism 

 appears, which is full of suggestiveness. 

 The peaks of the curves representing oxides 

 shift distinctly to the right of the curve 

 representing chlorides as the atomic weight 

 increases. Lithium marks a maximum with 

 both curves, but the oxygen curve lags 

 greatly at the succeeding peaks, having its 

 maximum with lanthanum at the atomic 

 weight 139,''^ and shifting over as far as 



" The essential data for discovering this gen- 

 eralization, namely, the heats of oxidation of the 

 metals having great afBjiity for oxygen, are as 

 follows: lithium, 72; sodium, 50; magnesium, 72; 

 potassium, 43; calcium, 76; rubidium, 42; stron- 

 tium, 71; csesium, 41; barium, 67, and lanthanum, 

 74. These values correspond with gram-equiva- 

 lents, that is, combination with eight grams of 

 oxygen, and are expressed in kilogram-calories. 

 The typical oxide is always meant. The figures 

 rest chiefly upon the recent work of Eengade, 



lead above 200. This simple fact standing 

 alone would perhaps mean but little, but 

 other similar facts seem to point in the 

 same direction. For example, the property 

 of electro-positiveness, exhibited by the 

 alkali metals, instead of reappearing in 

 copper, has been carried over with dimin- 

 ished intensity to zinc ; and finally, 

 among the higher atomic weights the cusp 

 has deserted mercury (the analogue of 

 zinc) and gone as far afield as thallium. 

 Clearly the rate of progression which de- 

 termines electro-positiveness has a longer 

 "wave-length" than that which determines 

 valence, if we may describe the periodicity 

 of these zigzag curves as waves. Again, the 

 tendency towards low melting point un- 

 questionably likewise progresses with a 

 longer "wave-length" than most of the 

 other properties. In the first complete 

 period, nitrogen, oxygen, fluorine and neon 

 all have very low melting points. At each 

 recurrence of these groups with higher 

 atomic weights the melting point rises, 

 whereas with each recurrence of the imme- 

 diately following alkali metals the melting 

 point falls. By the time antimony is 

 reached, this analogue of nitrogen has a 

 melting point as high as 900° absolute, 

 whereas the next alkali metal has the lowest 

 melting point of all these metals. Clearly 

 the property of melting has shifted toward 

 the right. Other examples of a similar 

 kind have been pointed out by others, 

 de Forcrand and Guntz. References to mos/ of 

 the papers are to be found in Abegg's "Hand- 

 buch der anorganischen Chemie. " The work of 

 Guntz is published in Compt. rend., 1903, 136, 

 p. 1071; 1905, 140, p. 863; Bull. Soo. cMm., 1906, 

 (III.), 35, p. 503. The work on lanthanum was 

 done by Matignon, Ann. CMm. Phys., 1906, 

 (VIII.), 8, p. 426. The heat of oxidation of 

 beryllium is not accurately known, but since the 

 oxide may be decomposed by magnesium at high 

 temperatures, the value is very probably less than 

 70 calories per gram-equivalent. 



