PRESIDENTIAL ADDRESS. l65 



isobaric 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 assump- 

 tion that they are isobarice. Thus the compounds formed from iron are 

 regarded as indicating the existence of three irons, aJl having the same 

 atomic weight. One 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 regai-ded as divisible into three classes : (1) Isotopic 

 elements, each set of which have different atomic weights but identical chemical 

 properties; (2) Isobaric elements which have identical atomic weights but 

 different chemical properties ; (3) Normal elements which differ from each other 

 both in atomic weights and chemical properties. 



The discovery of X-rays may be acclaimed as having added a new sense to 

 aid us in our investigation of material objects, and to 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 which represents the space in the atomic table the element 

 should occupy. The researches of Eutherford and Andrade on Lead and 

 Radium B have proved that ' isotopes ' have the same atomic number. What- 

 ever 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 a.ddition 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 tlie cases of tellurium 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 ele- 

 ments adopted by Newlands in his communication to the Chemical Society of 

 1866, in which he set forth the ' Law of Octaves,' the precursor of the Periodic 

 Law. 



In concluding this brief sketch, cognisance should be taken of the specula- 

 tions of physicists as to the structure of the atom. Already several models of 

 the atom are in the field which leave the uncuttable Daltonian atom far out of 

 view, still in a measure they help to an understanding of some of those regulari- 

 ties 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 of another nature, which 

 appear to me of interest to chemists, and to that extent have a hearing on 

 the welfare of chemistry in this country. 



Among the numerous revelations and surprises of the past five years has 

 been the realisation on the part of the public and the Government of the 

 importance of the chemical industries to the national well-being. The apathy 

 and indifference of pre-war times were replaced by an apparently lively interes't 

 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 of our industrial insufficiencies and emphasised 

 m various ways the importance of research in connection with our industries. 

 Again, the coal-tar colour industry furnished, as it had done again and again, 

 some thirtv. to forty years ago, the text from which research and its importance 

 was preached. This time the reiteration had the effect that the ' aniline 

 phantasm,' as I have seen it described, was recognised as a ' key industry,' 

 important to the vitality of the manufacture of textiles; with the result that 

 the Government, discarding its fiscal policy, was induced to subsidise the 

 1919. Q 



