54 Royal Society : — 



purposes, where a gentle and equable heat was required for several 

 hours. 



Pursuing my experiments with the oxides of the metals, heated 

 on wire gauze, I tried as many uo i could procure or make, and by 

 a tolerably wide induction I found that the sesquioxides have the 

 strongest tendency to produce and maintain the catalytic glow, and 

 do produce it in every case in which they are not decomposed by the 

 amount of heat required to begin the operation. 



When hydrated Fe., O., is heated and placed over alcohol, its colour 

 is deepened towards black, but not uniformly, and when cold the 

 original colour returns. But if it be made red-hot and quenched in 

 boiling alcohol out of contact with air, it is converted into hydrated 

 Fe.j O^. and remains permanently a deep black magnetic powder, 

 soluble in acids. A strong solution of ammonia may be substituted 

 for the alcohol with the same effect, but in this case some of the 

 sesquioxide will remain unaltered and mixed with the black oxide. 

 The alcohol or ammonia is correspondingly changed by oxidation 

 derived from the oxygen which has been released from combination 

 with the iron. If the hydrated Fe^ O^ be heated in contact with air, 

 it immediately (even when it has been kept for many months) be- 

 comes Fe., 0.5 by oxidation from the atmosphere, but if heated to red- 

 ness in vacuo, it cools unchanged. [Can the black powder of alu- 

 mina be AI3 Oj, formed in a similar way ?] The process of catalysa- 

 tion l)y Fe., O3 is thus evident ; the heated sesquioxide loses a por- 

 tion of oxygen to the alcohol and becomes Fe.^ O^, which is instantly 

 reconverted into Fe„ O3 by receiving oxygen from the air, and this 

 alternation is constantly going on in every portion of the glowing 

 mass. It is not a mere action cle presence, but alternate reduction 

 and oxidation of the sesquioxide, producing a continuous oxidation 

 of the alcohol. 



This suggests a consideration apparently adverse to the atomic 

 hypothesis of Dr. Dalton. How can a single comj)ound molecule 

 Fe, Og be changed by deoxidation into another compound molecule 

 FcyO^, when, according to theory, there are in it but two combining 

 proportions of iron, whereas the resultant contains three ? and how 

 (bjr deoxidation) can the resultant molecule contain /ok/- combining 

 proportions of oxygen when the primary contained only t/tree ? We 

 can indeed represent to the imagination that three molecules of the 

 sesquioxide, acting as if they were one triple molecule, lose otie com- 

 bining proportion of oxygen, and are converted into two molecules 

 of the black oxide ; and conversely, that two molecules of the black 

 oxide, acting as if they were 07ie double molecule, combine with one 

 atom of oxygen, and are converted into three atoms of sesquioxide. 

 'I'he only way to account for this, in accordance with the popular 

 atomic theory, seems to be, to assume that the notation for these 

 oxides is incorrect, and that 



for FcoOy we should write Fe^O^, 

 and for Fe., O^ we should write Fe^ Og. . 



If the current notation be retained, and any law be admitted, in 



