Attgust 25, 1881] 



NATURE 



397 



were they wonld cease to be elementary bodies at once, and 

 would be willed out of our tables. Nor do I think it possible 

 that in the present stage of our knowledge they can be revealed 

 to us in any otlier way than by the spectroscope. It is unfortu- 

 mte that none of these chemists who have given us this view 

 have helped us by showing in what way the possibility, which 

 all of them suggest, and which many of them intensely believe 

 in, could be absolutely demonstrated, but it is obvious that il 

 dissociation is the thing which time out of mind has made 

 compound bodies simpler, in their minds the condition of 

 liigher temperature must have been present. Tlie only difficulty 

 was the way in which the effects of that hi^h temperature could 

 be measured and weighed, and I think that if the spectroscope 

 had been introduced earlier they would probably have left some 

 hints behind them which would have been of the greatest value 

 to those who work with that instrument. 



Passing from the chemists to the physicists, there is one, at 

 all events, who has appreciated exactly how this decomposibility 

 of the terrestrial elements could bs established. I refer to the 

 lamented Clerk Maxwell. In his article on atoms in the 

 " Encyclopcedia Britannica," he says: "The discovery of a 

 particular line in a celestial spectrum which does not coincide 

 with any line in a terrestrial spectrum indicates either that a 

 substance exists in the heavenly body not yet detected by che- 

 mistry on earth, or " (and it is to the " or " X wish to draw atten- 

 tion) " that the temperature of the heavenly body is such that 

 some substance undecomposable by our methods is there split 

 up into components unknown to us in their separate "states." 

 Absolutely nothing could be clearer than this. 



la endeavouring to discuss the bearing of this application of 

 the hypothesis of evolution of chemical forms upon modern 

 chemistry, we must draw a very wide distinction between chemi- 

 cal theory and cliemical fact. 



When we compare the laws given in average chemical text- 

 Ijojks with the laws which lie at the root, let us say, of astronomy, 

 the candid mind cannot fail to be struck by the difficulty whicli 

 chemists must have encountered in endeavouring to reduce the 

 facts of their science to order on the hypothesis they bring before 

 us. An outsider, for instance, thinks that the basis of chemistry, 

 or a large part of the basis of chemistry at all events, lies in the 

 fact that the chemist has determined the existence of a certain 

 number of elementary bodies, each of these elementary bodies 

 having a certain atomic weight, and that this atomic weight 

 determines all the constants of that body. Vet we read in 

 chemical text-books that this atomic weight is fixed according 

 to no invariable rule ; indeed, with Kepler's laws and Newton's 

 laws in one's mind one comes to the conclusion tliat it is not too 

 much to say that it is determined by a series of compromises. 

 An outsider would think that if any one of these elementary 

 bodies were taken as a standard, the weight of an equal volume 

 of vapour of another substance under equal conditions would 

 bear some relationship of a definite character to the atomic 

 weight. This however is not the case. Again, among the 

 questions to be considered as determining the atomic weights 

 taken, is an assumed limitation of combination power, a so- 

 called atomicity, according to which one substance is a monad, 

 because it will combine with that same relative proportion of 

 hydrogen .which exists in half a water-molecule. Another sub- 

 stance is called a dyad, because it will combine with the same 

 relative proportion of hydrogen which exists in a whole water- 

 molecule, and so on. When we thus begin to class the sub- 

 stances into monads, dyads, hexads, and so forth ; in fact, 

 when we thus effect a re-classification of elementary bodies, the 

 solidarity at once breaks down ; we find that the classification 

 after all is useless, because the same substance may behave as a 

 dyad, a tetrad, a hexad, a pseudo-tryad, a pseudo-octad ; in 

 fact, one feels one is dealing with something that is moi-e 

 like a moral than a physical attribute— a sort of expression 

 of free will on the part of the molecules. We are, I think, 

 justified in asking whether these various attempts to formulate a 

 science do not break down after a certain point, because they 

 attempt to give a fixity to what is in truth variable. 



When we pass to the facts of tlie science, the key-note of 

 which is variability from one end of the scale to the other, we 

 find that the view of successive dissociations, the view of variable 

 molecular groupings brought about under different conditions, is 

 really more or less in accordance with the facts where the laws 

 based on the fixity of the facts break down entirely. Thus, for 

 instance, let us take the question of vapour densities. Tlie view 



accounts fully for the so-called anomalous vapour densities, and in 

 this way : it suggests that the elements may really be complex 

 groups which break up into their constituent groups under suit- 

 able conditions of temperature, like phosphoric chloride and 

 many other bodies do when obtained in the condition of vapour. 

 We have dissimilar groups in the one case, and possibly similar 

 groups in the other. In thi.s way, that contradiction in terms, 

 the "monatomic molecule," really becomes the evidence of a 

 higher law. 



Let us pass to allotropic conditions. The explanation of these 

 is that there are bodies which have a large molecular range 

 within the ordinary temperatures at our command. The sub- 

 stances in which allotropism is most marked are all metalloids 

 which have not been found in the sun, and the allotropic forms 

 give us in many cases different spectra — spectra indicating a 

 considerable complexity of the molecules which produce them — 

 spectra of continuous absorption, continuous radiation in the 

 blue, continu lus absorption in the red, fluted spectra, and the 

 like. In the passage from one allotropic condition to the other, 

 energy, without any known exception, is absorbed or given out. 

 What becomes of this energy ; whit is it doing ; unless it is in 

 some way or other controlling the passage from one molecular 

 group to another? These allotropic conditions, occnn-ing very 

 obviously to us in certain limits at our ordinary temperature and 

 pressure are, I hold, but special cases of group-condensation 

 common to all bodies, represented by Dalton's law of multiple 

 proportions. We can indeed imagine a condition of things in 

 which the difterence between iron in Fe,j, and the iron in FeXlj, 

 would be as obvious as the difterence between ordinary and 

 amorphous phosphorus. 



In certain classes of so-called organic substances this grouping 

 of simpler groups to more complex actually takes place, and is 

 recognised under the tenn polyoierism — for instance, with cyan 

 ogen compounds of oxygen we have a simple thing like CNO 

 say, which will form a -eries of compounds, and we have its so- 

 called polymers, C.iNjOj, or C3N3O.J, which will each form a 

 series of compounds, these groups of simpler nature forming 

 by their combination group individuals with related but not 

 identical properties with the simplest or fundamental gi-oup. 



In many cases the amount of this condensation may be deter- 

 mined by the v.ipour densities. In others, again, a dissociation 

 takes place at a certain limit of temperature, a simpler or funda- 

 mental group being the resolution product. 



The resemblance between these cases of polymerism and espe- 

 cially those elementary bodies which exhibit allotropism, is at 

 least striking. 



In the one case, the organic complex bodies, the range of 

 existence is in most cases within our easy attainment ; in the so- 

 called elementary stuffs it is less frequently the case. We can 

 certainly convert ordinary phosphorus and sulphur into allotropic 

 and most likely polymeric forms, but we do not know as yet how 

 many atoms more are contained in the polymeric forms of these 

 substances than in their simpler states. 



And in other substances this range of condition of formation 

 passes gradually out of our reach, but the phenomena are the 

 same in kind up to the temperature of the sun. And. again, 

 when we can obtain the spectra of bodies like amorphous phos- 

 phorus we can prophesy that the relative grouping of the atoms 

 of phosphorus in this to the ordinary form will be exhibited. 



This brings us to the next point — atomicity. What are the 

 associated phenomena? Lowest melting-point, simplest spec- 

 trum, lowest atomicity. Therefore we are justified, I think, in 

 assuming that atomicity may after all be but the measure of the 

 molecular groupings at work. In this way we can associate 

 various atomicities, not with moral phenomena as regards the 

 " behaziotir" of the same molecule, but with different physical 

 states — different complexities of the same substance. Thus in the 

 same substance the more complex or allotropic the molecular 

 grouping, the higher the atomicity. Hence the substances in 

 which the highest atomiticities appear should, as a rule, be 

 formed and br ken up at the lowest temperature. This, 1 am 

 informed, is really what happens in the majority of cases. 



New Analogies between Organic and Inorganic Bodies 

 I have ventured in these few remarks to touch upon the rela- 

 tions of the new view to modern chemical facts, because I think 

 such a discussion shows us that there are several chemical regions 

 in which the views can be tested from a chemical point of view, 

 although I have, from a set purpose in my lectures, dealt with 

 them absolutely from the physical side. In fact, one such 



