August 7, 1896.] 



SCIENCE. 



161 



covered. The properties including tlie im- 

 portant phj^sical constants of even tlie well- 

 known elements and their compounds are 

 quite imperfectly known. A great deal of 

 the future work of the chemist must be de- 

 voted to the detailed and patient studj^ 

 of the multitudinous compounds already 

 known, as well as to the formation of new 

 ones. 



The increased knowledge of the future 

 will render changes and modifications neces- 

 sary in any one of the present systems, or, 

 perhaps, will set all of them aside and 

 evolve out of them one which will perfectly 

 present the truths of the law. Understand- 

 ing the heading of this paper to refer then 

 not to the law itself, but rather to the pres- 

 ent arrangements of the elements under 

 that law, let us briefly look at some of the 

 diflBculties in their way. 



An impartial observer would notice first 

 the large number of unknown elements, 

 necessary for the completion of most of 

 these arrangements. MendeMefi" has blank 

 spaces for at least thirty-five new elements, 

 or, if a hydrogen period below lithium be 

 granted, then forty-one more elements must 

 be discovered somewhere, or more than one- 

 third of the total supposed number. It 

 would almost seem unreasonable to found 

 any system upon the imperfect knowledge 

 of less than two-thirds of the individuals to 

 be included in it, were it not borne in mind 

 that the ones now known constitute all but 

 a small fraction of the matter of which the 

 universe is composed, and again that they 

 fall in the system in regular consecutive 

 order, leaving only one unoccupied space 

 among the first fifty-two members accord- 

 ing to Mendeleeff. Even this blank has 

 been filled, if the recent discovery of an ele- 

 ment in monazite having an atomic weight 

 of approximately 100 be confirmed. 



Modifications of the Mendeleefi" system do 

 not require so large a number of additional 

 elements for their completion, eight or ten 



satisfying all apparent requirements. In 

 case the Mendeleeff" system is correct, where 

 are these to come from ? The close scrutiny 

 to which all terrestrial forms of matter have 

 been subjected by chemical and spectro- 

 scopic analysis leaves little material to be 

 called upon as the source of these elements. 

 Still the recent discoveries of argon and 

 helium teach us not to be too positive in 

 our exclusion of unknown elements because 

 of past investigations. The so-called rare 

 earths will unquestionably yield several 

 new elements. It seems a great pity that 

 this scarce and valuable material cannot be 

 collected and placed in the hands of some 

 patient investigators whose labors might be 

 supported from some research fund and who 

 could tell us then just what the science had 

 to expect from this source. A further 

 thought is that some of these elements may 

 not occur in nature, but that the future vadsy 

 teach us some way of synthesizing them, 

 and then the whole list can be filled out. 

 The brilliant victory over the difficulties 

 surrounding the chemistr}^ of the sugars 

 and their sjmthesis, filling out their system 

 so meagerly outlined in nature, would be 

 ground for encouragement as to possible 

 conquests among the elements. 



The anomalous position of hydrogen 

 forms a second objection to the Periodic 

 Law. It is not counted in anj^ of the 

 periods of seven or of seventeen. Its intro- 

 duction into any system in which the ar- 

 rangement depends upon increasing atomic 

 weight would throw out the sequence of the 

 elements. Placing hydrogen at the head of 

 the system, with connecting lines to all seven 

 of the first period, as has been done by some, 

 is a very questionable expedient. This is 

 simply an unjustifiable return to the Prou- 

 tian hypothesis, and is a violent distortion 

 of all the facts concerning valence, positive 

 and negative properties etc, for which the 

 table is supposed to stand, and lastly it does 

 not relieve the anomaly of the position. 



