166 PROCEEDINGS OF THE AMERICAN ACADEMY 



fall naturally into two series, with the common difference of 5 for 

 the perissads and perhaps 4 for the artiads. The latter series, 

 however, is somewhat indefinite. 



Between ICO and 150 the perissads increase regularly, with a com- 

 mon difference of about G|, and the artiads less regularly, with the 

 same difference, as shown in Tables I. and II. 



Too little is known of the atomic weights between 150 and 190, and 

 of those above 210, to justify their classification. Between 1 90 and 210, 

 we find that 4 applies to 195, 199 * 207, and to 196, 200, 204, 208. 



All of the first series are artiads, and in the second all except 200, 

 or II g, are recognized as perissads, and this element is so similar in 

 many respects to Cu, Ag, and Au that for the present it is allowed to 

 remain in its place. There only remain unclassified 9, 14, 59, 104, 

 and 193. Of these numbers, 9 is the atomic weight of Be and ap- 

 pears to differ too much from 8, the serial number of this element, to 

 be recognized in its natural place. 



The remaining numbers, 14, 59, 104 * 193, form a series by them- 

 selves, with a difference of a little less than 45. Ni and Co correspond 

 to 59, Ru and Rh to 104, and Ir to 193. These elements are always 

 classified together, and this regularity of increase has often been 

 noticed. But perhaps 14, or N, falls into this series accidentally. 



In Tables I. and II. the first column shows the symbols for the ele- 

 ments ; the second column, the serial numbers derived from the for- 

 mula; the third column, the observed atomic weights; and the fourth 

 column, the deviations from the serial numbers. The next columns 

 show the specific gravity, the atomic volume, the fusibility, mallea- 

 bility, and place in an electro-chemical series for each element, and the 

 last column the group in the classification of Newlands and Mende- 

 leeff to which the element has been assigned. The horizontal lines 

 divide the series and periods of this system. 



The observed atomic weights are taken from the lists of Clarke,* 

 L. Meyer,f and Van der Plaats,$ and in most cases by selecting for 

 each element that one of the values that differs least from the mean, 

 taking oxygen at 1G for a standard, and expressing but one place of 

 decimal fractions. The data for the next four columns are taken 

 from Meyer's " Modern Theories." To express their fusibility, the 

 elements are divided into seven classes, that represented by 1 being 

 the most fusible. The brittle and malleable elements are distinguished 



* The Constants of Nature. A Recalculation of Atomic Weights, 1882. 

 t Modern Theories of Chemistry, English Translation, 1888. 

 t Verification of the Atomic Weights of M. Stas. 



