OF ARTS AND SCIENCES. 167 



by the initial letters B and M. la the electro-chemical series taken 

 from Barker's " Text-Book of Chemistry," * 1 is the most electro-posi- 

 tive in an acid solution, and 63 the most negative. 



It appears from these tables that none of the deviations from the 

 serial numbers exceed 0.6 excepting that for Cb among the perissads, 

 and Zn and Mo among the artiads ; Zn differs by just a unit, and 

 seems to foim an exception to the regularity. 



In his account of the Discovery of the Periodic Law,t Newlands 

 points out the irregularity of the single series, illustrating it by several 

 tables, and the data are clearly set forth and tabulated in a recent 

 paper by Venable, on the Recalculation of the Atomic Weights. J 



In the artiad grand group no atomic weight corresponds to 20, 36, 

 83, or 131, and a reference to the electro-chemical series will show 

 that these are the points at which the elements change from a negative 

 to a positive maximum, corresponding also to the maximum atomic 

 volumes, and to the end of the MendeleefF periods. 



These points are marked with asterisks in the table. 



Analogy points to the possibility of elements with atomic weights 

 of 15, 43 or 44, 47, 60, and perhaps of 99, 100, and 143.5. 



The newly discovered philippium and praseodymium may perhaps 

 correspond to 47 and 143.5, respectively, but there appears to be no 

 place in either series for neodymium or 140.3. 



In each of the grand groups, perissads and artiads, the breaks be- 

 tween the minor groups of common difference occur at or near the 

 minimum points of the series of atomic volumes, and therefore mid- 

 way between the dividing lines above mentioned. 



The first term of each of the groups of common difference, except 

 the first, viz. Ga, Ag, Au, Ge, Pd, and Pt, appears to be a heav}' 

 malleable metal, electrically neutral, and with an atomic volume a 

 little above 9 in the artiad, and 10 in the perissad groups. 



With the increase of atomic volume is generally associated an in- 

 crease in electro-negative properties, and, as a rule, the elements be- 

 come fusible, brittle, and diamagnetic. 



With the maximum atomic volume, the elements change from the 

 extreme of negative to positive, from diamagnetic to magnetic, from 

 brittle to malleable ; and with the decrease of volume, they lose their 

 electro-positive properties, and, as a rule, become at last brittle and 

 infusible. 



* Text-Book of Chemistry, p. 16. 



t The Periodic Law, p. 27. 



i Journal of Analytical Chemistry, January, 1889, p. 48. 



