214 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



These two run partly parallel with one another; but a deviation 

 in the parallelism appeal's, 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 lan- 

 thanum at the atomic weight 139, 1 and shifting over as far as 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 diminished 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 determines electro-positiveness has a longer "wave-length" 

 than that which determines valence, if we may describe the perio- 

 dicity of these zigzag curves as waves. Again, the tendency toward 

 low melting point unquestionably 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 immediately following alkali metals the melting point falls. 

 By the time antimony is reached, this analogue of nitrogen has a 

 meltino- point as high as 900° absolute, whereas the next alkali metal 

 has the lowest melting point of all these metals. Clearly the prop- 

 erty of melting has shifted toward the right. Other examples of a 

 similar land have been pointed out by others, for example, the well- 

 known displacement from strict periodicity of argon, cobalt, and 

 tellurium all point to an unequal rate of progression in isolated cases. 

 Thus, this phenomenon seems to be a general one; the various prop- 

 erties of material seem to oscillate with varying rhythms as the 

 atomic weights increase. The variation is so great that one may 

 almost suspect not only varying rhythms but also rhythms repre- 

 sented by different types of mathematical functions. 



These facts suggest a possible reason for the great irregularity of 

 the last part of the periodic table. May it not be that the nature 



i The essential data for discovering this generalization, namely, the heats of oxidation of the metais having 

 great affinity for oxygen, are as follows: Lithium, 72; sodium, 50; magnesium, 72; potassium. 43; calcium 

 76; rubidium, 42; strontium, 71; caesium, 41; barium, 67, and lanthanum, 74. These values correspomd 

 with gram-equivalents, that is, combination with 8 grams of oxygen, and are expressed in kilogram- 

 calories. The typical oxide is always meant. The figures rest chiefly upon the recent work of Rengade. 

 de Forcrand and Guntz. References to most of the papers are to be found in Abegg's "Handbuch der 

 anorganischen Chemie." The work of Guntz is published in Compt. rend., 1903, vol. 136,p. 1071; 1905, vol. 

 140,p.803; Bull.Soc.chiin.,1906(iii),vol. 35,p.503. The work on lanthanum was done by Matignon, Ann. 

 Chim. Phys., 1900 (viii), vol. 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. 



