THE CHEMICAL ELEMENTS.

'We do not know that any one of the bodies denominated elementary is absolutely indecomposable.'-DALTON.

I HAVE recently announced to the Royal Society that, reasoning from the phenomena presented to us in the spectroscope when known compounds are decomposed, I have obtained evidence that the socalled elementary bodies are in reality compound ones.

Although the announcement took this form, which was as sober and as unsensational as I could make it, the interest taken in science now-a-days by the general public is so great, that it is apt to travel beyond the record, and as newspaper editors are not content to wait for what the experimentalist himself has to say, they are often at the mercy of those who, perhaps more from a sanguine temperament than anything else, are prepared to provide columns filled with statements wide of the mark. Nor is this all: if there be a practical side to the work, some application of science' is brought to the front, and the worker's own view of his labour is twisted out of all truth.

This has happened in my case. The idea of simplifying the elements is connected with the philosopher's stone; the use of the philosopher's stone was to transmute metals; therefore I have been supposed to be 'transmuting' metals; and imaginations have been so active in this direction that I am not sure that when my paper was eventually read at the Royal Society, many were not disappointed that I did not incontinently then and there 'transmute' a ton of lead into a ton of gold.

It is in consequence of this general misapprehension of the nature of my work, that I the more willingly meet the wishes of the Editor that I should say something about it in the Nineteenth Century. The paper itself I need not reproduce, as it has appeared in extenso in Nature, but there are many points touching both the origin of the views I have advanced and the work which has led up to them, on which I am glad of the opportunity of addressing a wider public.

I.

It is now upwards of ten years since I began a series of observations having for their object the determination of the chemical constitution of the atmosphere of the sun. The work done, so far as

the number of elementary substances found to exist in it, I summed up in an article printed in the last July number of this Review, but the ten years' work had opened up a great number of problems above and beyond the question of the number of elements which exist in the solar atmosphere, because we were dealing with elements under conditions which it is impossible to represent and experiment on here.

In the first place, the temperature of the sun is beyond all definition; secondly, the vapours are not confined; and thirdly, there is an enormous number of them all mixed together, and free, as it were, to find their own level. Nor is this all. Astronomers have not only determined that the sun is a star, and have approximately fixed his place in nature as regards size and brilliancy, but they have compared the spectrum of this star, this sun of ours, with those of the other bodies which people space, and have thus begun to lay the foundations of a science which we may christen Comparative Stellar Chemistry. Dealing with the knowledge already acquired along this line, we may say roughly that there are four genera of stars recognisable by their spectra.

We have first the brightest and presumably hottest stars, and of these the spectrum is marvellously simple-so simple, in fact, that we say their atmospheres consist in the main of only two substances

a statement founded on the observation that the lines in the spectra are matched by lines which we see in the spectra of hydrogen and calcium; there are traces of magnesium, and perhaps of sodium too, but the faintness of the indication of these two latter substances only intensifies the unmistakeable development of the phenomena by which the existence of the former is indicated.

So much, then, for the first class: now for the second. In this we find our sun. In the spectra of stars of this class, the indications of hydrogen are distinctly enfeebled, the evidences by which the existence of calcium has been traced in stars of the first class are increased in

intensity, and, accompanying these changes, we find all simplicity vanished from the spectrum. The sodium and magnesium indications have increased, and a spectrum in which the lines obviously visible may be counted on the fingers is replaced by one of terrific complexity.

The complexity which we meet with in passing from the first class to the second is one brought about by the addition of the lines produced by bodies of chemical substances of moderate atomic weight. The additional complexity observed when we pass from the second stage to the third is brought about by the addition of lines due in the main to bodies of higher atomic weight. And this is a point of the highest importance at the third stage the hydrogen, which existed in such abundance in stars of the first class, has now entirely disappeared.

In the last class of stars to which I have referred, the fourth, the lines have given place to fluted bands, at the same time that the light and colour of the star indicate that we have almost reached the stage of extinction.

These facts have long been familiar to students of solar and stellar physics; indeed, in a letter written to M. Dumas, December 3, 1873, and printed in the Comptes Rendus, I thus summarised a memoir which has since appeared in the Philosophical Transactions:

Il semble que plus une étoile est chaude plus son spectre est simple, et que les éléments métalliques se font voir dans l'ordre de leurs poids atomiques.1

Ainsi nous avons :

1. Des étoiles très-brillantes où nous ne voyons que l'hydrogène, en quantité énorme, et le magnésium;

2. Des étoiles plus froides, comme notre Soleil, où nous trouvons:

Hydrogène + Magnésium + Sodium

Hydrogène + Magnésium + Sodium + Calcium + Fer,

dans ces étoiles, pas de metalloïdes ;

3. Des étoiles plus froides encore, dans lesquelles tous les éléments métalliques sont ASSOCIÉS, où leurs lignes ne sont plus visibles, et où nous n'avons que les spectres des métalloïdes et des composés.

4. Plus une étoile est âgée, plus l'hydrogène libre disparaît; sur la terre, nous ne trouvons plus d'hydrogène en liberté.

Il me semble que ces faits sont les preuves de plusieurs idées émises par vous. J'ai pensé que nous pouvions imaginer une dissociation céleste,' qui continue le travail de nos fourneaux, et que le metalloïdes sont des composés qui sont dissociés par la température solaire, pendant que les éléments métalliques monatomiques, dont les poids atomiques sont les moindres, sont précisément ceux qui résistent même à la température des étoiles les plus chaudes.

Before I proceed further, I should state that while observations of the sun have since shown that calcium should be introduced between hydrogen and magnesium for that luminary, Dr. Huggins' photographs have demonstrated the same fact for the stars, so that in the present state of our knowledge, independent of all hypotheses, the facts may be represented as follows:2

I have no hesitation in stating my opinion that in this line of facts we have the most important outcome of solar work during the last ten years, and if there were none others in support of them the

1 The old system of atomic weights was the one referred to.

2 Symbols are used here tɔ save space. H-Hydrogen, Ca➡ Calcium, Mg➡ Mag. nesium, Na Sodium, Fe = Iron, Bi Bismuth, Hg Mercury.

conclusion would still stare us in the face that the running down of temperature in a mass of matter which is eventually to form a star, is accompanied by a gradually increasing complexity of chemical forms.

This then is the result of one branch of the inquiry, which has consisted in a careful chronicling of the spectroscopic phenomena presented to our study by the various stars.

Experimentalists have observed the spectrum of hydrogen, of calcium and so forth in their laboratories, and have compared the bright lines visible in the spectra with the dark ones in the stars, and on this ground they have announced the discovery of calcium in the sun or of hydrogen in Sirius.

In all this work they have taken for granted that in the spectrum thus produced in their laboratories, they have been dealing with the vibration of one specific thing, call it atom, molecule, or what you will; that the vibrations of these specific molecules have produced all the lines visible, which they have persistently seen and mapped in each instance.

II.

It is at this point that my recent work comes in, and raises the question whether what has been thus taken for granted is really true. And now that the question is raised, the striking thing about it is that it was not asked long ago.

One reason is this. Time out of mind-or, rather, ever since Nicolas Le Fèvre, who was sent over here by the French king at the request of our English one at the time the Royal Society was established, pointed out that chemistry was the art of separations as well as of transmutations—it has been recognised that with every increase of temperature, or dissociating power, bodies were separated from each other. In this way Priestley, from his 'plomb rouge' separated oxygen, and Davy from potass separated potassium; and as a final result of the labour of generations of chemists, the millionfold chemical complexity of natural bodies in the three kingdoms of nature has been reduced by separations till only some sixty socalled elements are left.

Now this magnificent simplification has been brought about by the employment of moderate temperatures-moderate, that is to say, in comparison with the transcendental dissociating energies of electricity as employed in our modern voltaic arcs and electric sparks.

But, in the observations made during the last thirty years on the spectra of bodies rendered incandescent by electricity, we have actually, though yet scarcely consciously, been employing these transcendental temperatures, and if it be that this higher grade of heat does what all other lower grades have done, then the spectrum

we have observed in each case is not the record of the vibrations of the particular substance which we have put into the arc and with which we have imagined ourselves to be working alone, but of all the simpler substances produced by the short or long series of the 'separations' effected.

The question, then, it will be seen, is an appeal to the law of continuity, nothing more and nothing less. Is a temperature higher than any yet applied to act in the same way as each higher temperature, which has hitherto been applied, has done? Or is there to be some unexplained break in the uniformity of nature's processes?

The definite reason for my asking the question at the present time has been this. The final reduction of four years' work at a special branch of the subject to which I will refer presently, on the assumption that at the temperature of the electric arc we do not get such simplifications,' has landed me in the most hopeless confusion, and if I do not succeed in finding a higher law than that on which I have been working, my four years' work, in this direction at all events, will have missed its aim.

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III.

This and other reasons compel, me to hold that the answer to the question put is, that these transcendental temperatures do dissociate, and that therefore what has hitherto been taken for granted is, in all probability, not true. But before I proceed to give the reasons for the faith that is in me, I must, at the risk of being both technical and tedious when I should wish to be neither, lead up to the understanding of the arguments I have used.

IV.

The spectroscope, however simple or complex it may be, is an instrument which allows us to observe the image of the slit through which the light enters it, in the most perfect manner. If the light contains rays of every wave length, then the images formed by each will be so close together that the spectrum will be continuous, that is, without break. If the light contains only certain wave lengths, then we shall get certain, and not all, of the possible images of the slit, and the spectrum will be discontinuous.

Again, if we have an extremely complex light source, let us say a solid and a mixture of gases giving us light, and we allow the light to enter, so to speak, indiscriminately into the spectroscope, then in each part of the spectrum we shall get a summation-a complex record-of the light of the same wave length proceeding from all the different light waves. But if by means of a lens we form an image of the light-source, so that each particular part shall be impressed in its proper place on the slit plate, then in the spectrum the different kinds of light will be sorted out.