produced by Cdtalytic Bodies. 197 



has proved to be the case with regard to atoms of water, and 

 we know of numberless instances in the case of oxides. Thus 

 RO uniting with oxygen forms ROg. In this case RO + O 

 corresponds to RO + A, the acid here representing the chlo- 

 rous element from its oxygenous character. It is not neces- 

 sary to suppose that A and O are associated in one continu- 

 ous line, the probability being that the molecule may really 

 be represented by ARO. Thus also in Rg O3, where the O3 

 are probably grouped equally round Rg, there is room for 

 three more of a chlorous element to gratify the dual affinity, 

 and the general formula Rg Og, 3A is the result, the 3A here 

 representing three of a simple chlorous element. The result, 

 as regards affinity;, will still however be the same, the whole 

 '. depending upon the attraction of the central nucleus R. It 

 ig therefore only for simplicity of expression in studying the 

 phaenomena of catalysis, that I view the atoms of oxygen of 

 an acid as associated in mechanical continuation with the 

 atoms of oxygen of the base, the ejf'ect being represented by 

 this expression : the whole views of molecular or atomic con- 

 stitution of bodies are in my opinion only convenient fictions 

 to enable us to study the forces themselves, and the concep- 

 tion of a mechanical arrangement I only adopt as expressive 

 of the manifestations of powers residing in matter. 



To show that the tendency of bases to N O5, even without 

 being combined, is to attach themselves to the oxygenous 

 part of the acid, a curious phaenomenon observed by Mercer 

 may be cited. 



A portion of alumina may be taken and placed at the bot- 

 tom of a vessel containing warm NO5 ; no action ensues, ex- 

 cept partial solution ; a slip of calico coloured in indigo-blue 

 may now be introduced into the mixture, and remains unaf- 

 fected in the clear acid, but is immediately discharged when 

 pressed with a glass rod into the alumina. Here the alumina 

 acts by placing the oxygen of the nitric acid in a state of ten- 

 sion without however succeeding in decomposing it, but the 

 moment an assistant affinity comes into play, that state is 

 shown by the decomposition of the nitric acid and oxidation 

 of the indigo. The alumina in the presence of the acid could 

 not oxidize (in fact, we know of no higher oxide), and there- 

 fore the indigo appropriates the oxygen. I find that various 

 other oxides, such as calcined Crg O3 and SnOg, have the same 

 power, the latter showing this disposition more strongly than 

 any of the other oxides. The best mode of trying these ex- 

 periments is to heat a certain quantity of nitric acid, and then 

 dilute it till indigo cloth ceases to be bleached. The oxide of 

 tin is now added and allowed to fall to the bottom. On in- 



