IS 15.] An Address to Chemists. 125 



ment guided and accompanied by speculation, that can give us new 

 information. Let me be allowed here to give an example. Hydrate 

 of iron is so cemposed that the oxygen of the oxide is twice that of 

 the water; but both Mr, Dalton and myself give to this oxide three 

 atoms of oxygen. This hydrate, then, is F O^ + 1^ H -O. I 

 should certainly be disposed to explain this at once, by supposing 

 that tlie oxide of iron contains six atoms cf oxygen. But in order 

 to see whether there he other proofs for such an idea, let us run 

 over the comljinations of the oxide of iron with other bodies. Let 

 us examine, for example, the combinations of this oxide with acids 

 which contain six atoms of oxygen, but which in their neutral 

 saline combinations contain only three times as much oxygen as the 

 base. If in these neutral combinations with these acids, the .red 

 oxide of iron does not constitute an exception to the general law, it 

 ought likewise to contain six atoms of oxygen ; for otherwise in the 

 arseniale or chromate of iron there would be for each atom of iron 

 half an atom of arsenic or chromium. Let us extend these re- 

 searches still farther, and examine if the arseniates, chromates, &c. 

 can be formed with oxides in which there is evidently no more than 

 three atoms of oxygen, &c. The ultimate result of our researches 

 will probably be that four and six atoms of oxygen, instead of three, 

 are much more general than we have hitherto supposed ; and that 

 not only oxide of iron, but silica and various other oxides contain 

 in fact six atoms of oxygen instead of three. 1 suppose that Mr. 

 Dalton will agree with me that by such researclies we may render 

 mucli more complete the beautiful theory for which he feels himself 

 so much interested, and for which we are in a great measure in- 

 debted to him. 



1 have considered it as a great difficulty attached to the atomic 

 theory that it does not explain the laws concerning the combina- 

 tions of the oxides with each other, namely, why the ox3'gen in the 

 one is always a multiple by a whole number of that in the otiier. 

 Mr. Dalton removes this difficulty by saying, " It is not the peculiar 

 business of the atomic theory to explain it any more than to show 

 why all the metallic oxides do not mutually combine with each 

 other." But we must recollect that the principal circumstance in 

 favour of the atomic theory is, that it gives a mechanical and very 

 satisfactory cause why elementary atoms unite only in jjroportions 

 wliich are multiples of eacli other. We have observed likewise 

 that the compound atoms, that is to say, most of those which 

 contain oxygen, combine likewise in a mi/hiplex ralio, provided we 

 attend only to the oxygen which they contain. It is clear that this 

 must be owing to a cause similar to that which occa-^ions similar 

 proportions between elementary atoms ; but the atomic theory 

 throws no light on the subject. 'J'his must be admitted a^ some- 

 thing still wanting in tlie theory ; for wiicn a theory only explaiijs 

 one half of the plienomcna which result from the [)rinciple which 

 regulates these phenomena, it is surely incomplete. 1 differ, then, 

 from Mr. Dalton, and must continue to coni.iclcr the atonn'c theory 



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