64 



DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



perty of the heated glass, which it has in common with the bodies named above. 

 They state that liquids do not show this effect, at least that mercury, at or below the 

 boiling point, has not the power ; that it is not due to porosity ; that the same body 

 varies very much in its action, according to its state ; and that many other gaseous 

 mixtures besides oxygen and hydrogen are affected, and made to act chemically, 

 when the temperature is raised. They think it probable that spongy platina acquires 

 its power from contact with the acid evolved during its reduction, or from the heat 

 itself to which it is then submitted. 



612. MM. DuLONG and Thenard express themselves with great caution on the 

 theory of this action ; but, referring to the decomposing power of metals on ammonia 

 when heated to temperatures not sufficient alone to affect the alkali. They remark that 

 those metals which in this case are most efficacious, are the least so in causing the 

 combination of oxygen and hydrogen ; whilst platina, gold, &c., which have least 

 power of decomposing ammonia, have most power of combining the elements of water; 

 from which they are led to believe, that amongst gases, some tend to unite under the 

 influence of metals, whilst others tend to separate, and that this property varies in 

 opposite directions with the different metals. At the close of their second paper they 

 observe, that the action is of a kind that cannot be connected with any known theory; 

 and though it is very remarkable that the effects are transient, like those of most 

 electrical actions, yet they state that the greater number of the results observed by 

 them are inexplicable, by supposing them to be of a purely electric origin. 



613. Dr. FusiNiERi has also written on this subject, and given a theory which he 

 considers as sufficient to account for the phenomena*. He expresses the immediate 

 cause thus : " The platina determines upon its surface a continual renovation of con- 

 crete lamince of the combustible substance of the gases or vapours, which flowing over 

 it, are burnt, pass away, and are renewed : this combustion at the surface raises and 

 sustains the temperature of the metal." The combustible substance, thus reduced into 

 imperceptible laminoe, of which the concrete parts are in contact with the oxygen, is 

 presumed to be in a state combinable with the oxygen at a much lower temperature 

 than when it is in the gaseous state, and more in analogy with what is called the 

 nascent condition. That combustible gases should lose their elastic state, and become 

 concrete, assuming the form of exceedingly attenuated but solid strata, is considered 

 as proved by facts, some of which are quoted in the Giornale di Fisica for 1824 -J-; and 

 tliough the theory requires that they should assume this state at high temperatures, 

 and though the similar films of aqueous and other matter are dissipated by the action 

 of heat, still the facts are considered as justifying the conclusion against all oppo- 

 sition of reasoning. 



614. The power or force which makes combustible gas or vapour abandon its 

 elastic state in contact with a solid, that it may cover the latter with a thin stratum 

 of its own proper substance, is considered as being neither attraction nor affinity. It 



* Giomale di Fisica, &c., 1825, torn. viii. p. 259. t PP. 138, 371. 



