OCTOBEK 27, 1911] 



SCIENCE 



541 



mathematical relationship between atomic 

 weights would afford us an immeasurably 

 precious insight into the ultimate nature 

 of things. 



But weight is only one of the funda- 

 mental properties of an element. Volume 

 is almost, if not quite, as important in its 

 own way, although far more variable and 

 confusing. All gases, indeed, approach 

 closely to a simple relationship of volumes, 

 defined by the law of Gay Lussae and the 

 rule of Avogadro, and well known to you 

 all. In the liquid and solid state, however, 

 great irregularities are manifest, and very 

 little system as regards volume is generally 

 recognized. 



About twelve years ago, the study of 

 such small irregularities as exist among 

 gases led me to the suspicion of a possible 

 cause for the greater irregularities in 

 liquids and solids.^ On applying van der 

 Waals's well-known equation to several 

 gases, in some tentative and unpublished 

 computations, it seemed clear that the 

 quantity & is not really a constant quan- 

 tity, but is subject to change under the 

 influence of both pressure and temperature. 

 This conclusion has also been reached inde- 

 pendently by van der Waals himself.^" 

 But if the quantity h (supposed to be de- 

 pendent upon the space actually occupied 

 by the molecules) is changeable, are not the 

 molecules themselves compressible?" 



The next step in the train of thought is 

 perhaps equally obvioiis. If changes in 



" Richards, ' ' The Significance of Changing 

 Atomic Volume," Froc. Amer. Acad., 1901, 37, 

 p. 1; 1902, 37, p. 300; 1902, 38, p. 293; 1904, 39, 

 p. 581; Zeitsch. physilcal. Chem., 1902, 40, pp. 169, 

 597; 1903, 42, p. 129; 1904, 49, p. 15. 



" Van der Waals, Zeitsch. pTiysikal. Chem., 1903, 

 28, p. 257. His earlier publication on this topic 

 {Froc. B. ATcad. Wetensch. Amsterdam, 1898, 29, 

 p. 138) was unknown to me at that time. See also 

 Lewis, Froc. Amer. Acad., 1899, 35, p. 21. 



" Van der Waals speaks cautiously, but with 

 some conviction, as to the probable compressibility 

 of the molecules on p. 283 of the paper cited above. 



the bulk of molecules are to be inferred 

 even from gases, may not the expansion 

 and contraction of solids and liquids afford 

 a much better clue to the relative expansion 

 and contraction of these molecules? 



Most physical chemists refer all changes 

 in volume to changes in the extent of the 

 empty space between the molecules. But 

 are there, after all, any such empty spaces 

 in solids and liquids 1 Solids do not behave 

 as if the atoms were far apart within them ; 

 porosity is often conspicuous by its absence. 

 Take, for instance, the case of glass; the 

 careful experiments of Landolt on the con- 

 servation of weight^ ^ show that glass is 

 highly impermeable to oxygen, nitrogen 

 and water for long periods. Such porosity 

 as occurs in rigid, compact solids usually 

 permits the passage only of substances 

 which enter into the chemical structure of 

 the solids themselves. Thus, nitrogen can 

 not free itself from imprisonment within 

 hot cupric oxide, although oxygen can es- 

 cape ;^^ again, water can not evaporate into 

 even the driest of atmospheres from acci- 

 dental incarceration in crystals lacking 

 water of crystallization.^* Palladium, on 

 occluding hydrogen, is obliged to expand 

 its bulk in order to make room for even this 

 small addition to its substance. The be- 

 havior of platinum, nickel and iron is prob- 

 ably analogous, although less marked." 

 Fused quartz, impermeable when cold, al- 

 lows of the passage of helium and hydrogen 

 at high temperatures;'" but most other 

 gases seem to be refused admission, and 



^ H. Landolt, ' ' Ueber die Erhaltung der Masse 

 bei chem. XJmwandlungen, " Abhandlung der 

 Iconigl. preuss. ATcad. der Wissenschaften, 1910. 



" Eichards, Zeitsch. anorg. Chem., 1892, 1, p. 

 196; Froc. Amer. Acad., 1893, 28, p. 200. 



" Baker and Adlam, J. Chem. Soc. Trans., 1911, 

 99, p. 507. 



'■'Richards and Behr, Fubl. Carnegie Inst., 1906, 

 No. 61. 



" Jacquerod and Perrot, Compt. rend., 1907, 144, 

 p. 135. 



