470 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



11 The curve ... is divided by five maxima 1 into six sec- 

 tions, which have somewhat the form of a series of suspended 

 chains, of which the second and third, and likewise the 

 fourth and fifth, are similar to one another and occupy nearly 

 equal portions of the horizontal axis. 



" If one considers now the placing of the elements on the 

 curve, one finds in corresponding places on similar portions 

 of the curve elements with similar properties. 



" All easily melted, volatile and gaseous elements are on 

 ascending branches of the curve : those fusible with difficulty 

 ... on descending branches. . . near the minimum," where 

 also are found the few elements that do not obey the law of 

 Dulong and Petit, and so forth (Ann. Chem. Pharm., 1870, 

 7, Suppl., 359-363). 



The chief feature of the atomic volume curve (Fig. 52, 

 pp. 472 473), as Lothar Meyer points out, is its subdivision 

 into a series of six catenary curves, which correspond with the 

 first six periods of the modern table of the elements shown on 

 p. 462. In the region covered by the two short catenaries 

 II and III, Newlands's Law of Octaves may be applied 

 with little modification, but the long catenaries IV and V 

 (which form an equally close pair), indicate clearly that the 

 interval between analogous elements is now much greater 

 than an octave ; the atomic volume curve thus makes the 

 distinction between the short and long periods compulsory 

 rather than optional. 



The subsequent course of the curve is less certain. 

 Lothar Meyer represented the whole of the elements from 

 caesium 133 to bismuth 208, as lying upon a single big 

 catenary VI, corresponding with the big period VI of 32 

 elements shown in Tables 2, 3 and 4. Later writers, fol- 

 lowing Mendeleeff, have assumed that there are two 

 long periods here, separated by a maximum occupied by 

 an unknown alkali-metal. But there is no experimental 



1 Corresponding, in Lothar Meyer's curve, with the five alkali- 

 metals. 



