August 8, 1907] 



NA TURE 



355 



Arrhenius, pursuing the nnalogy which exists between 

 the laws governing matter in the gaseous state and in 

 the state of dilute solution, had previously been led to 

 the view that the electrical conductivity of flames contain- 

 ing salt-vapours was due to ionisation of the salt through- 

 out the volume of the flame. It appeared possible there- 

 fore that the luminosity might be ascribed likewise to 

 the metal separated in the ionic state. Experimental 

 investigation undertaken with a view to elicit inform- 

 ation on this subject seemed to favour the view that the 

 metal was reduced by chemical processes, and that it 

 glowed in the un-ionised condition. Evidence seemed to 

 point to the conclusion that, for example, when common 

 salt is introduced into the flame of coal-gas the sodium 

 chloride yields sodium by the conjoint action of steam and 

 reducing gases ; when liberation of the metal w'as pre- 

 vented by adding a large quantity of hydrochloric acid to 

 the flame the glow disappeared, but the conductivity was 

 not always diminished. The fact that sodium salts, in- 

 cluding the chloride, impart their characteristic glow to 

 the flame of cyanogen and to other flames in which water 

 is absent leads to some difHculty in finding a chemical 

 explanation, and it must be admitted that a direct thermal 

 dissociation of an alkaline halide or oxide is not out of 

 the question. The interval of detachment of the metallic 

 atom may be exceedingly brief, but it must be remembered 

 that even so short a time as the interval between the 

 molecular encounters in a gas at a high temperature is 

 still sufficient for the emission of thousands of undisturbed 

 characteristic vibrations. The experiments to which I 

 have alluded have been followed up with great industry 

 and success by Prof. H. A. Wilson, who has added much 

 to our knowledge of the electrical condition of the flames 

 containing vaporised salts ; but the question of the con- 

 dition of the luminous gas is still far from being settled. 

 Very interesting and important investigations have been 

 carried out by Lenard, who has shown that the stream 

 of luminous vapour produced from a sodium salt in a 

 Bunsen flame is deflected in an electric field in such a 

 way as to indicate that the vapour is positively charged ; 

 but he gives reason for believing that the charged con- 

 dition is intermittent with the neutral condition. The 

 lines in the spectrum of an alkali metal are divisible, as 

 is well known, into distinct groups or series, in each of 

 which the oscillation frequencies corresponding with the 

 lines are in a definite mathematical relationship. The 

 principal series, which include the lines seen individually 

 as such in ordinary flame spectra, are, according to 

 Lenard, due to the electrically neutral atoms. In a salted 

 spirit flame, and in other flames of low temperature where 

 only lines of the principal series are represented, the 

 stream of luminous gns does not behave in an electric 

 field as if it were charged. In the flame of coal-gas burnt 

 in a Bunsen burner the salt-vapour gives, in addition to 

 the distinct lines of the principal series, diffuse bands of 

 luminosity on the dark background, which, according to 

 Lenard, represent the undeveloped subordinate series ; and 

 it is the atoms emitting these series that are deflected in 

 the electric field. It is inferred, therefore, that the light 

 in a salted Bunsen flame comes from different groups of 

 centres of emission — the principal series from the neutral 

 atom, and the lines of the first, second, and third sub- 

 ordinate scries from atoms w-hich have lost respectively 

 one, two, and three electrons. Lenard goes further, and 

 shows that the salt-vapour in a Bunsen flame, as in the 

 flame of the electric arc. emits these different kinds of 

 radiation from different structural regions; thus the 

 vapour at the edge of the flame is electrically neutral and 

 gives only the lines of a principal series. 



The negative electricity in a salted flame would, accord- 

 ing to Lenard, be disembodied, and recent cxneriments by 

 Gold confirm the view that the negative carrier in flames 

 is a free electron. In connection with this subject I 

 ought to allude to an investigation by Tufts, which seems 

 to throw .some doubt on the conclusions which w^re drawn 

 from the experiments made by Prof. Wilson. Dr. Dawson, 

 and myself; and I must also mention an important con- 

 tribution to the subject recently made by Prof. Hartley, 

 in which considerable light is thrown upon the chemical 

 changes undergone by compounds of the alkaline earth 

 metals when they are introduced into flames, and upon 



NO. 197 I, VOL. 76] 



the relation of these changes to the various spectral 

 features. I am afraid, however, that it would be weari- 

 some if I were to prolong this summary, and I must 

 be content to leave it without doing justice to those who 

 are engaged upon the work. The subject is obviously 

 one of fundamental importance in relation to spectrum 

 analysis, and my own slight connection with it has only 

 strengthened my opinion that there is still a great deal 

 connected with the genesis of spectra that requires the 

 attention of the chemist even more than that of the 

 physicist. Spectrum analysis arose under the joint in- 

 fluence of Bunsen and Kirchhoff, and I think its problems 

 still call for more combined work on the part of chemist 

 and physicist than has latterly been the custom. 



Having given a short summary of the present state of 

 knowledge on one particular chemical topic, I may perhaps 

 be permitted to conclude my Address with a few general 

 observations relating to the science as a whole. 



The contemplation of such a life as that of Berthelot 

 makes us realise in a vivid way the progress of chemical 

 science. He was a chemist without limitation, his- 

 activity extending over the whole range of the science, 

 physical, inorganic, and organic. Whilst w'e must not 

 forget his exceptional powers, we cannot help feeling how 

 different in its extent was our science when he entered 

 upon his labours from what it was when they ceased, and 

 we cannot help feeling how vain it now is for anyone to 

 hope for so imperial a sway. 



Yet it is difficult to believe that the state of chemistry 

 can ever have been more interesting than it is at the 

 present moment, or that anyone who sighs for the good 

 old times can do so from anything but the love of a quieter 

 life. We need not go back more than twenty years to 

 find a sharp contrast, .^t that time there was indeed no 

 want of activity, but it w'as that of a band of travellers 

 who had left their frontier adventures far behind, and 

 were marching steadily over a wide and almost un- 

 interrupted plain. To-day we are among the mountains, 

 with new peaks and prospects appearing on every side. 

 Truly a steady head is required; and well may we ask. 

 Whither are we going and where is the path of progress 

 and of safety? I rejoice to live in such times; but I feel 

 no competence to describe them, still less can I pretend 

 to have vision keen and comprehensive enough to let me 

 figure as a guide. 



One of the penalties of devotion to a progressive science 

 is the constant feeling of being left behind, and the know- 

 ledge that, while we are attending to our personal task, 

 things are happening, near or far, that may, for all we 

 know, be affecting the simplest facts and the most 

 elementary principles on which we have been accustomed 

 to rely. This is a feeling that may well prevail at the 

 present day. .^t the same time I do not think there is 

 any occasion for panic, and I cannot help regretting the 

 somewhat sensational language that has been used, even 

 within our own circles, in regard to recent discoveries. 

 The revelations attendant upon the investigation of radio- 

 activitv do indeed mark a distinct epoch in the history 

 of chemical discovery, but that they entail anything like 

 an unsettlement of our scientific articles of faith is not 

 to be admitted for a moment. They make us realise in 

 perhaps a not unprofitable way that scientific knowledge 

 and scientific theories are necessarily proximate, never 

 ultimate, and that ideas which may have been entertained 

 for a long time without modification, and so have begun 

 to seem perpetual, are, after all, only provisional. 



There is certainly some embarrassment on finding that 

 a substance like radium, which according to the conven- 

 tions would be called a chemical clement, breaks up so 

 as to give substances which, according to the same con- 

 ventions, are likewise called elements. But the confusion 

 is one of terminology and not of ideas. I think it likely 

 that few chemists of my own generation have been in- 

 the habit of regarding the conventional elements as the 

 ultimate compositional units of matter. We know that 

 in our own country distinguished men of science like Sir 

 William Crookes and Sir Norman Lockyer have always 

 insisted on the complex nature of the elements, and T 

 suspect there are manv among us who might own to 

 having made sober, if unsuccessful, attempts at the resolu- 

 tion of elements before the davs of radium. 



