September i8, 1919] 



NATURE 



61 



Theory of Matter " he has given us conceptions of 

 how atoms may be constituted to provide a series 

 so related that they reflect, if not reproduce, many 

 of the chemical characters of the elements and their 

 periodic relation to atomic weights. 



With the discovery of radium and its remarkable 

 properties we have been brought in contact with an 

 element undreamt of in our philosophy. The inter- 

 pretation of the results of the investigation of this 

 element has called for drastic changes in our con- 

 ception of an element. The pursuit of the researches 

 of the radio-active elements, guided by the theory of 

 the spontaneously disintegrating atom propounded tv 

 Rutherford and Soddy, has served to reveal facts 

 which lend a special emphasis to many passages in 

 the address of Sir W. Crookes to vifhich 1 have alreadv 

 referred. 



For instance, the passage in which he said : " Should 

 it not sometimes strike us, chemists of the present 

 day, that after all we are in a position unpleasantlv 

 akin to that of our forerunners, the alchemists of the 

 Middle Ages? The necromancers of a time long past 

 did not, indeed, draw so sharp a line as do we between 

 bodies simple and compound; yet their life-task was 

 devoted to the formation of new combinations, and to 

 the attempt to transmute bodies which we commonlv 

 consider as simple and ultimate — that is, the metals. In 

 the department of synthesis they achieved verv con- 

 siderable successes ; in the transmutation of metals 

 their failure is a matter of history." 



Or again, when he propounded the question : " Is 

 there, then, in the first place, any direct evidence of 

 the transmutation of any supposed ' element ' of our 

 existing list into another, or of its resolution into 

 anything simpler?" — a question to which he, Sir 

 William Crookes, was at that time forced to reply 

 in the negative, whereas to-day many instances might 

 be cited in support of an affirmative answer to this 

 question. Radio-activity has supplied a method of 

 analysis — radio-active analysis — surpassing in delicacy 

 any of the previously known methods for the 

 examination of material substance; the application 

 of these methods has not only added to the list of 

 Clements, but also new classes of elements. First, 

 elements indistinguishable and inseparable by chemical 

 means, yet differing slightly but definitely in their 

 atomic weights. The existence of these "isotopes," 

 as Soddy styles them (a name giving prominence to 

 the fact that such elements occupy the same place in 

 the table of the elements), demonstrates that absolute 

 uniformity in the mass of every ultimate atom of the 

 same chemical element is not an essential, but that 

 "our atomic weights merely represent a mean value 

 around which the actual atomic weights of the atoms 

 \ arv within certain narrow limits " (Crookes, Address 

 to Section B, 1886). 



Whether the possibility of separating isotOf>es, 

 recently suggested by Dr. Lindemann and Dr. Chap- 

 man, will be found capable of experimental realisation, 

 must be left to the future to decide ; in fact, in this 

 matter we must adopt the attitude, prevalent in other 

 than scientific circles, of "wait and see." 



The investigations in the field of radio-activity have 

 further brought to light that identity in atomic weight 

 may be associated with difference in chemical pro- 

 pfrties, revealing the existence of a further class of 

 elements for which Dr. Stewart suggests the name 

 "isobares." Further, Dr. Stewart considers that iso- 

 baric elements are to be found, not alone amongst the 

 radio-active, but some of the normal elements exhibit 

 properties which may be explained on the assumption 

 that they are isobarics. Thus the compounds formed 

 from iron are regarded as indicating the existence of 

 three irons, all having the same atomic weight. One 



NO. 2603, VOL. 104] 



of these, termed ferricum, is tervalent; one, ferrosum, 

 is divalent; whilst the third, ferron, is inert and takes 

 no part in chemical changes. The three are, under 

 certain conditions, mutually interconvertible. This 

 last condition does not apply in the case of the radio- 

 active isobares. 



The elements are to be regarded as divisible into 

 three classes : — (i) Isotopic elements, each set of 

 which have different atomic weights but identical 

 chemical pro{>erties ; (2) isobaric elements which have 

 identical atomic weights but different chemical pro- 

 perties; and (3) normal elements which differ from 

 each other both in atomic weights and chemical pro- 

 perties. 



The discovery of X-rays may be acclaimed as having 

 added a new sense to aid us in our investigation of 

 material objects, and among their innumerable services 

 may be reckoned the results which have followed from 

 the investigations of the X-ray spectra of the elements 

 by the late Lieut. Moseley, whose death in Gallipoli 

 in 1915 is one of the many tragedies of the war 

 specially deplored in the scientific world. From the 

 analysis of the X-ray spectra Moseley has shown that 

 for each element a value can be deduced, which 

 is styled the atomic number and represents the 

 space in the atomic table the element should occupy. 

 The researches of Rutherford and .Andrade on lead 

 and radium B have proved that "isotopes " have the 

 same atomic number. Whatever may be the ultimate 

 explanation of the meaning of the atomic numbers, 

 their experimental determination has. already proved 

 valuable in the solution of some of the anomalies of 

 the periodic table. In addition to the case of isotopes, 

 just referred to, the number of elements between 

 hydrogen and uranium is fixed by finding 92 as the 

 atomic number for uranium, and, further, Moseley's 

 work has revealed that the atomic numbers are in 

 agreement with the order .of the chemical sequence, 

 rather than the order of the atomic weights, which 

 is of special interest and value in the cases of tel- 

 lurium and iodine, and of potassium and argon, the 

 decision in each case proving a welcome support to 

 the position in the table assigned to these elements 

 on chemical considerations. 



Again, Moseley's atomic numbers remind us of the 

 arrangement of the elements adopted by Newlands in 

 his communication to the Chemical Society of 1866, 

 in which he set forth the "law of octaves," the pre- 

 cursor of the periodic law. 



In concluding this brief sketch, cognisance should 

 be taken of the speculations of physicists as to the 

 structure of the atom. Already several models of the 

 atom are in the field which leave the uncuttable Dal- 

 tonian atom far out of view; still, in a measure they 

 help to an understanding of some of those regularities 

 exhibited by the elements, and set forth in the natural 

 system. Valency and its vagaries, which we are 

 accustomed to describe by phrases such as "variable 

 valency," "selective valency," and the like, still call 

 for a full explanation. 



I purpose now to direct attention to matters cf 

 another nature, which appear to me of interest to 

 chemists, and to that extent have a bearing on the 

 welfare of chemistry in this country. 



Among the numerous revelations and surprises cf 

 the past five years has been the realisation on the 

 part of the public and the Government of the import- 

 ance of the chemical industries to the national well- 

 being. The apathy and indifference of pre-war times 

 were replaced by an apparently lively interest in things 

 chemical, and there was what in the religious world 

 would be styled a revival. 



Politicians, the Press in all its varied forms, daily, 

 weekly, monthly, and quarterly, took up the subject 



