1823.] Combination of Elastic Fluids. STO 



by experiment. If the proportions of the gaseous mixture differ 

 much from those which form water, or if an incombustible gas, 

 such as azote, be present, the combination goes on slowly, the 

 temperature is but little increased, and water soon condenses in 

 the re<jeiver. 



If the spongy platina be strongly calcined, it loses the pro-» 

 perty of becoming red hot ; but in this case, it effects the com-» 

 bination of the two gases slowly, and without any very sensible 

 increase of temperature. Platina reduced to a very fine powder, 

 by well-known chemical means, does not act upon the gases 

 even slowly, at common temperatures, nor do platina wires or 

 bars. The agreement of these observations may give rise to the 

 idea, that the porosity of the metal is an essential condition ii^ 

 the production of the phenomenon ; but the following facts dis-* 

 prove this conjecture. 



We reduced platina to leaves as thin as the malleability of the 

 metal would allow of. In this state, the platina acts at common 

 temperatures upon the mixture of hydrogen and oxygen, and the 

 action is more rapid when the foil is thinnest. We obtained 

 some which effected the detonation in a few seconds. But 

 what renders this action still more extraordinary is the physical 

 condition indispensable to its production, A very thin sheet of 

 platina rolled on a glass cylinder, or freely suspended in a deto- 

 nating mixture, produced no sensible effect after a lapse of seve-? 

 ral days. The same sheet of platina, if crumpled, acts instanta^ 

 . neously, and causes the mixture to detonate. 



The leaves disposed as we have described, and which produce 

 no effect at common temperatures, the wires, powder, and thick 

 bars of platina, which are inefficient under the same eircum<p 

 stances, act slowly, and without producing explosion at a tem^ 

 perature of 400° to 572° according to their thickness. 



We have found that other metals possess the same property a^ 

 platina. The very remarkable fact discovered by Su' H. Davy 

 during his researches on the safety lamp, viz. that wires of platina 

 and palladium at a low temperature become bright-red wheii 

 immersed in a detonating mixture, having appeared to us to be 

 derived from the same cause as the phenomenon under discussion, 

 we were first induced to try palladium. 



The piece which we made use of was given to one of us by 

 Dr. WoUaston, and consequently must be considered as free 

 from alloy ; nevertheless we were unable to reduce it to very 

 thin leaves, as it cracked under the hammer. We attribute to 

 this circumstance its possessing no action at the temperature of 

 the atmosphere ; but it acted at least as well as platina of the 

 same thickness at a high temperature. Rhodium being brittle 

 could not be subjected to the same preparation ; but it occasioned 

 the formation of water at a temperature of about 464° of Fahr. 



Gold and silver in thin leaves act only at high temperatures, 

 but always below that of boiling mercury. Silver is less power- 



