1 92 Dr. Playfair on Transformations 



cheaply as a substitute for a captive balloon in meteorological 

 inquiries, or even (on a very extensive scale) for other require- 

 ments in military science, &c. An anemometer, a thermo- 

 meter, an hygrometer, &c. of some registering kinds, &c., 

 might be hauled up and lowered at pleasure (like a flag) by a 

 person standing in the centre of the triangle (above referred 

 to), and by means of a line passing through a little block 

 attached to the kite. The cords and kite should of course be 

 of pure silk, for»the sake of lightness, combined with extreme 

 strength, and the size and thickness in some measure adapted 

 to the breeze or lighter air. The silk might be advantageously 

 covered with a very light coat of elastic varnish. 



XXXV. On Transformations produced by Catalytic Bodies. 

 By Lyon Playfair, Esq,^ 



T> ERZELIUS rendered a most useful work to science, when 

 ■^-^ he collected into one class those varied phaenoraena of 

 chemical action resulting from causes certainly very different 

 from the ordinary manifestations of those affinities, which 

 produce combinations or promote decompositions. This phi- 

 losopher believes the power f? which causes decomposition 

 without the acting body participating in its result, to be a 

 distinct electro-chemical agency different from other recog- 

 nised powers, and he named it the " Catalytic force." Ac- 

 cording to this view, catalytic bodies do not act by chemical 

 affinity, but they excite inherent affinities in other substances, 

 in consequence of which new combinations or decomposi- 

 tions ensue. 



Mitscherlich J, adopting this view, considered a number of 

 catalytic decompositions in detail, and showed the important 

 influence exerted by the state of surface of bodies in favouring 

 this peculiar action, which he denominates decomposition by 

 contact. The examples, adduced in this interesting memoir, 

 of the favourable action of an extended surface upon combi- 

 nation, fully prove that the physical condition of bodies ex- 

 ercises an important influence upon the action of this force ; 

 but they do not remove the necessity for studying the force 

 itself, as it may either be a vis occulta, entirely distinct from 

 powers already recognised, as Berzelius supposes, or may be 

 modified forms of those in continual operation. 



Liebig§ views the catalytic power as a dynamical action 



* Communicated by the Chemical Society ; having been read April 5, 

 1847. 



"t" Jahresbericht, xv. 237. 



X Taylor's Scientific Memoirs, Part xiii. ; or Fogg. Ann, xxxi. 281. 



§ Liebi^'s Chem. of Agriculture, 4th edit., p. 284. 



