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tact with the platina wires or plates, which had acted as poles j for 

 under these circumstances they gradually diminished in volume, water 

 was reproduced, and at last the whole of the gases disappeared. On 

 inquiring into the cause of this reunion of the elements of water, the 

 author found that it was occasioned principally by the action of the 

 piece of platina, which had served for the positive pole ; and also that 

 the same piece of platina would produce a similar effect on a mixture 

 of oxygen and hydrogen gases obtained by other and more ordinary 

 kinds of chemical action. By closer examination, it was ascertained 

 that the platina, which had been the negative pole, could produce the 

 same effect. Finally, it was found that the only condition requisite 

 for rendering the pieces of platina effective in this recombination of 

 oxygen and hydrogen is their being perfectly clean, and that ordinary 

 mechanical processes of cleaning are quite sufficient for bringing them 

 into that condition, without the use of the battery. Plates of platina, 

 cleaned by means of a cork, with a little emery and water, or dilute 

 sulphuric acid, were rendered very active ; but they acquired the 

 greatest power when first heated in a strong solution of caustic alkali, 

 then dipped in water to wash off the alkali, next dipped in hot strong 

 oil of vitriol, and finally left for ten or fifteen minutes in distilled 

 water. Plates thus prepared, placed in tubes containing mixtures of 

 oxygen and hydrogen gases, determined the gradual combination of 

 their elements : the effect was at first slow, but became by degrees 

 more rapid; and heat was evolved to such a degree, indeed, as fre- 

 quently to give rise to ignition and explosion. 



The author regards this phenomenon as of the same kind as that 

 discovered by Davy in the glowing platina ; that observed by Dobe- 

 reiner in spongy platina, acting on a jet of hydrogen gas in atmo- 

 spheric air ; and those so well experimented on by MM. Dulong and 

 Thehard. In discussing the theory of these remarkable effects, the 

 author advances some new views of the conditions of elasticity at the 

 exterior of a mass of gaseous matter confined by solid surfaces. The 

 elasticity of gases he considers as being dependent on the mutual ac- 

 tion of the particles, especially of those which are contiguous to each 

 other 5 but this reciprocity of condition is wanting on the sides of the 

 exterior particles which are next to the solid substance. Then, rea- 

 soning on the principle established by Dalton, that the particles of 

 different gases are indifferent to one another, so that those of one gas 

 may come within almost any distance of those of another gas, what- 

 ever may be the respective degrees of tension in each gas among the 

 particles of its own kind, he concludes that the particles of a gas, or 

 of a mixture of gases, which are next to the platina, or other solid body 

 not of their own chemical nature, touch that surface by a contact as 

 close as that by which the particles of a solid or liquid body touch 

 each other. This proximity, together with the absence of any mutual 

 relation of the gaseous particles to particles of their own kind, combined 

 also with the direct attractive force exerted by the platina, or other 

 solid body, on the particles of the gases, is sufficient, in the opinion 

 of the author, to supply what is wanting in order to render effective 

 the affinity between the particles of oxygen and hydrogen ; being, in 



