538 



SCIENCE. 



[N. S. Vol. II. No. 43. 



whicli would form a continuation of the 

 second period and whicli, following out the 

 above order, would have an atomic weight 

 between 35.45 and 39.11 and a valency of 

 or 8. A valency of would imply ab- 

 sence of combining power, in other words, 

 great inertness and molecules consisting of 

 single atoms, both of which characterize 

 argon. As pointed out above, the atomic 

 weight of argon may prove to be less than the 

 upper limit of 39.11. 



Lecoq de Boisbaudran and Julius Thom- 

 sen have advanced hypotheses which con- 

 sist essentially in the assumption of an 

 eighth group of elements, intermediate be- 

 tween and transitional from the halogens 

 to the alkali metals. Thomsen's table is 

 here given, the hypothetical transitional 

 elements being printed in heavy type. It 

 is otherwise simply an abbreviated form of 

 Lothar Meyer's table of the Periodic Sys- 

 tem. The dashes represent some of the 

 missing elements above referred to, and the 

 dots places of elements omitted for the 

 sake of clearness. 



I. Hydrogen 1 — — — 4 



II. Lithium-fluorine 7 9 11 12 14 16 19 20 



III. Sodium-chlorine 23 24 27 28 31 32 35.5 3G 



IV. Potassium-bromine 39 40 79 SO S4 



V. Rubidium-iodine 85 87 125 127 132 



VI. Cffisium 133 137 — — 212 



The atomic weights 4 and 36 would cor- 

 respond to the chief ingredients of what 

 we now call helium and argon. It must 

 be borne in mind that the figures in the 

 last column may be altered several units 

 without affecting the theory. 



It has been shown, however, as above 

 stated, that helium and perhaps argon 

 are more or less contaminated with 

 other new elements. Until the atomic 

 weights of these contaminating substances 

 have been determined, it would be useless 

 to assign them places in Thomsen's sys- 

 tem. There are several possibilities. They 

 may be other members of the last column. 



Instead of only one transitional element 

 between each period there may be several, 

 and we would have, instead of only one, 

 two or even three new columns on the 

 right of the table. There remain several 

 places open between hydrogen and lithium, 

 and we cannot at present deny the possi- 

 bility of unknown elements even preced- 

 ing hydrogen. Although this element heads 

 the list, there is no evidence of a natural 

 reason for its occupying this unique posi- 

 tion. On the hypothesis of a common ori- 

 gin of the elements from one primitive sub- 

 stance, the ' protyle ' of Crookes, the exist- 

 ence of such substances is by no means 

 improbable. The most exact atomic weight 

 determinations indicate that the true unit 

 of the whole system, the greatest common 

 divisor of all atomic weights, if it exists at 

 all, must be a comparatively small fraction 

 of the atomic weight of hydrogen, a mass 

 which could give rise to several elements 

 still lower in the scale. The discovery of 

 such elements would be scarcely more sur- 

 prising than that of helium, and that they 

 have not been thus far detected, even by 

 the spectroscope, is no more remarkable 

 than that tliis instrument overlooked argon. 

 While Thomsen's view cannot at present 

 be regarded as more than a suggestion, it is 

 certainly the one which best accords with 

 our present knowledge. The Periodic Sys- 

 tem, imperfect as it still is, bears unques- 

 tionable evidence of some fundamental na- 

 tural law, but it is at present as great a 

 mysteiy as the natural system of plants 

 and animals before the daj'S of the evolu- 

 tion theorjr. The problem which the chem- 

 ist faces to-day has much resemblance to 

 that which confronted the biologist in those 

 times. There appears to be no reason for 

 expecting the recent discoveries to be in any 

 way revolutionary, but they will doubtless 

 contribute to the solution of the great prob- 

 lem of the chemist, not only bj^ the en- 

 larged conceptions which they iuvolve, but 



