162 



SCIENCE. 



[N. S. Vol. IV. No. 84. 



A second supposition that hydrogen is 

 the initial member of a period of seven 

 which precedes Mendeleeff's typical ele- 

 ments, but which are as yet unknown, is 

 much more plausible. The discovery of 

 helium, and perhaps another element with 

 very low atomic weight, lends strength to 

 this supposition. Certainly the present 

 anomalous position of hydrogen is a serious 

 blot upon the system. 



Wurtz has pointed out two difficulties in 

 the system, both of which bear upon the 

 nature of periodicity. The first is the lack 

 of regularity in the differences between suc- 

 cessive elements, and the second is that the 

 gradations in properties do not seem to de- 

 pend upon the degree of these differences. 

 It has been also pointed out that the use of 

 the term periodic in the case of these varia- 

 tions is not a strictly mathematical one, and 

 that these periods, in passing from negative 

 to positive values, should pass through a 

 transition stage of either zero or infinity. It 

 is true that very little has been done to dis- 

 cover the nature or the laws of this so- 

 called periodicity, though some of the modi- 

 fications of Mendeleeff's table make some 

 points clearer and remove some difiiculties. 

 Chemists have generally contented them- 

 selves with calling any successive increases 

 or decreases in properties periodic, whether 

 they exhibited any regularity or not. This 

 is too slovenly and unsatifactory for a true 

 science, and those who love the science must 

 labor to remove such a reproach. The ob- 

 stacles to success are first inaccurate knowl- 

 edge of the properties, and in some cases the 

 absence of any definite standard of measure- 

 ment for these properties. 



Minor difiiculties lie in the relative posi- 

 tion of certain elements. Some are far from 

 satisfied with the position assigned the triad, 

 iron, cobalt and nickel. In some respects 

 they are out of line with some of the elements 

 apparently closely allied to them. Perhaps 

 when what Blanchard has called ' cross an- 



alogies ' are better understood these matters 

 will be made clearer. 



In the cases of at least two sets of ele- 

 ments, tellurium and iodine, and cobalt and 

 nickel, the very best determinations of their 

 atomic weights would place them in differ- 

 ent relative positions from those demanded 

 by the periodic sj^stem. These determina- 

 tions have been repeatedly revised in the 

 past few years, and yet the system still 

 seems at fault. Which is wrong, the system 

 or the investigations of the atomic weights ? 

 So many difiiculties surround these deter- 

 minations, and so many chances for errors 

 lie in their paths, that most will decide in 

 favor of the system and call for more thor- 

 ough and patient search after impurities 

 and imperfections of methods in the pre- 

 vious determinations. 



The discovery of argon and helium has 

 been regarded by some as giving a most 

 telling blow to the periodic system. Arti- 

 cle after article has been written on their 

 possible position in the system. Several 

 originators of systems have claimed to have 

 predicted these new bodies. No supposed 

 property nor absence of property staggers 

 these prophets. They have foreseen every- 

 thing. The whole question is, however, 

 premature. Manifestly the position of any 

 newly discovered element cannot be fixed 

 until two things are definitely settled: first, 

 the elemental character ; and secondly, the 

 more salient properties, as atomic weight, 

 valence, etc. These questions are yet to be 

 settled for the substances named, and there 

 are some serious difficulties in the way of 

 those investigating them. Until these ques- 

 tions are answered nothing can be done, and 

 certainly a system which has answered ad- 

 mirably for so many of the elements is not 

 to be given up on the half knowledge and 

 half guess-work which surround the two 

 newly found bodies. 



F. P. Yenable. 



University of Noeth Caeolina. 



