/;/ determining Gaseous Combination, 355 



marked preeminence of platina, and of a few metals closely 

 allied to it in chemical properties, over all other metals and 

 solid bodies that have been the subjects of experiment. Thus 

 platina has been shown to induce gaseous union at so low a 

 temperature as —4° Fahrenheit*, and palladium and gold in 

 the form of plates, and rhodium and iridium in the state of 

 powder, at atmospheric temperatures. All other metals and 

 solids are entirely inert at the temperature of the atmosphere, 

 and, with the exception of silver and osmium, require, in order 

 to effectuate gaseous union, to be heated nearly to the boiling 

 point of mercury. Now the statical condition of the film of 

 gaseous niatter contiguous to the metallic superficies (one of 

 the causes assigned by Dr. Faraday of greater density in that 

 portion of the gaseous mixture) being quite independent of 

 the nature of the bounding solid, must cause an equal degree 

 of condensation upon all the metals, and, indeed, upon all con- 

 tinuous surfaces. The attractive force (the other postulate in 

 Dr. Faraday's theory) may be supposed to be of variable 

 amount in different solid bodies. But no experimental proof 

 has yet been given that platina possesses a stronger attraction 

 than the other metals for gaseous fluids; on the contrary, the 

 experiments of Magnus f have shown that iron, nickel, and 

 cobalt absorb or condense the different gases to a large 

 amount. 



The following experiments (in several of which I was in- 

 debted for valuable assistance to my friend Mr. Joseph Ran- 

 some,) were designed to investigate the cause of the inferiority 

 of the other metals to platina in determining the union of hy- 

 drogen and oxygen. Since these actions, whatever be their 

 essential character, manifestly reside on surfaces, it seemed 

 probable that by employing the metals in that state in which 

 they present the largest amount of superficial extension, and 

 by thus augmenting the energy of the operating forces, their 

 true nature might be unfolded. Mechanical processes seemed 

 inadequate to ensure an absolutely untarnished surface ; and 

 the chemical agents, employed with success by Dr. Faraday, 

 for cleansing the surface of platina, were obviously inapplica- 

 ble to the oxidizable metals. The most promising mode of 

 obtaining this class of metals in the requisite state of purity 

 and mechanical division appeared to consist in precipitating 

 them from their salts in the condition of oxides, and in re- 

 ducing those oxides by heating them in hydrogen gas. 



Several preliminary experiments showed that bright copper 

 turnings, zinc-foil, iron turnings, box-wood charcoal recently 



* Delarive and Marcet, Ann. de Cliim. et de Phys., torn, xxxix. p. 328. 

 t Ann. de Chinu et de Phys.y torn. xxx. p. 103. 



2 Z2 



