July 6, 1900-] 



SCIENCE. 



33 



point. Following Dr. Venable* we may 

 assume that each of the first seven groups 

 consists of a group element, as in group one, 

 lithium, a type element as sodium, and two 

 series, one of more positive elements as 

 potassium, rubidium and cesium, and the 

 other more negative, as copper, silver and 

 gold. Further, the more positive the type 

 metal, the more closely will the metals of 

 the positive series resemble it ; the more 

 negative the type metal, the more closely 

 will the negative series resemble it. Thus in 

 the first group, the positive series potassium, 

 rubidium and cesium closely resembles the 

 type element sodium ; in the seventh group 

 the negative series, bromium and iodin, 

 resembles the type element chlorin. Now 

 the eighth group differs materially from the 

 other seven in that it contains three series, 

 with no group or type element. These three 

 series are transitional from the least posi- 

 tive among the seven positive series, man- 

 ganese, to the least negative among the 

 negative series, copper, silver and gold. 

 The properties of the metals of group eight 

 show this transition as from a chemical 

 standpoint, iron, cobalt and nickel form a 

 direct gradation between manganese and 

 copper. Now comes a further question as 

 to possible transition elements between the 

 most negative series, fluorin, chlorin, bro- 

 min, iodin, and the most positive series 

 sodium, potassium, rubidium and cesium. 

 From a theoretical standpoint such transi- 

 tion elements should be neither positive 

 nor negative, and should have a valence of 

 zero. A few years ago the realization of 

 such a conclusion would have seemed im- 

 possible, yet since the discoveiy of argon 

 and its congeners, it seems almost probable 

 that these places have been filled in accord- 

 ance with theory. If we take the most 

 generally accepted atomic weights, we find 

 helium preceding lithium, neon following 

 fluorin and preceding sodium, and argon, 

 * See periodic table. 



really between chlorin and potassium, but 

 with an atomic weight apparently slightly 

 greater than that of potassium which fol- 

 lows it, resembling in this respect cobalt 

 and nickel of this same group, and also 

 tellurium and iodin. There would, in ad- 

 dition, be expected from the analogies of 

 group eight, one, two, or three transitional 

 elements between bromin and rubidium, of 

 atomic weight, SO to 85, and Ramsay has 

 suggested that krypton may belong in this 

 place — so also an element or elements of 

 similar character might be expected be- 

 tween iodin and cesium, with atomic weight 

 of about 130. The recently published work 

 of Ladenburg and Kruegel on krypton give 

 it an atomic weight of about 59. This 

 would, as Professor Ladenburg suggests, 

 make it immediately precede copper, but 

 unless we change very materially our ideas 

 of the periodic law, it is difficult to conceive 

 of an element with the properties of kryp- 

 ton lying between nickel and copper. If 

 these inert gases belong in the eighth group 

 it may seem strange that iron and the other 

 familiar metals which belong here should 

 be so unlike such a type element as argon 

 or neon ; it must, however, be borne in 

 mind that this is only an expected exagger- 

 ation of the departures found in the first 

 and seventh groups, where copper departs 

 from its type element sodium, and mangan- 

 ese from its type element chlorin. As to 

 whether three elements are to be expected 

 of atomic weight 150 between the light and 

 the heavy platinum metals we have little 

 data upon which to theorize. As a matter 

 of fact, there is very little definite knowl- 

 edge of the elements between cerium and 

 tantalum. The inter- Jovian planet proved 

 to be an indefinitely large number of aster- 

 oids ; Sir William Crookes' study of the 

 rare earths leads him to the conception 

 of a group of asteroidal meta- elements in 

 this vacant space in the periodic table. 

 We must await further knowledge be- 



