produced by Catalytic Bodies. 193 



on the atoms of a complex molecule, conceiving that the ac- 

 tivity of the atoms of a body in a state of motion may be 

 communicated to those of another body in a state of rest. 

 The atoms of a compound, according to this view, if in a state 

 of exact statical equilibrium, arrange themselves according to 

 new affinities, when the vis inertice is overcome by motion. 

 In proof of this view, Liebig carefully examines a large num- 

 ber of decompositions, and accounts for some of the most 

 difficult transformations in organic chemistry. 



But there are many instances, to which I shall have to 

 draw attention in the present memoir, where catalytic de- 

 compositions ensue when there is no intestine motion in the 

 atoms of the exciting body ; and hence we cannot do more 

 than consider motion as favourable to the development of 

 dormant affinities, in a manner similar to the surface action 

 described by Mitscherlich. The power of peroxide of hy- 

 drogen and of pyruvic acid to reduce oxide of silver is cer- 

 tainly a singular phaenomenon, and appears favourable to 

 Liebig's views ; but the cause of the original decomposition 

 of the peroxide of hydrogen cannot be ascribed to motion, as 

 the atoms of the oxide of silver are not in that state, and 

 those of the peroxide of hydrogen either not at all or only 

 slightly so. Neither will it suffice to suppose that the escape 

 of gas during such decompositions is due to the presentation 

 of angular points from which the gas may escape *, because 

 solutions of alkalies equally effect the decomposition, accord- 

 ing to Thenard -f. The cause, therefore, which enables cer- 

 tain substances to hasten the decomposition of such bodies 

 as peroxide of hydrogen or persulphuret of hydrogen, al- 

 though favoured by the state of surface and by motion, is in- 

 dependent of mere physical condition. 



In further proof of the importance of motion in causing com- 

 bination or decomposition, Liebig cites the favourable effects 

 of agitation on the precipitation of potash by tartaric acid. It 

 may be questioned, however, whether this is not either a me- 

 chanical breaking up of a combination or the simple effect of 

 cohesion. Thus when water is saturated with a gas, a brisk 

 agitation with a rod causes the separation of bubbles of gas 

 previously dissolved. The mechanical force may here be sup- 

 posed to have broken up the compound molecule of water and 

 gas by detaching the former, and thus enabling the gas to 

 escape by its elasticity. In the precipitation of potash by 

 tartaric acid, cohesion may effect the same result that elasti- 

 city does in the case of gas, the agitation knocking off the 



• Ann. der Pharm., ii. 22. 



f Ann. de Chim. et de Phys., xlviii. 79. 



Phil. Mag. S. 3 . Vol. 3 1 . No. 207. Sept. 1 847. O 



