DR. DAUBENY ON THE ERUPTION OF VESUVIUS. 159 



of the lava at the same time disengaged ; that a portion of what was originally ejected 

 still continues in a compressed state within the cavities of the rock, especially in its 

 interior ; and that it is only by slow degrees that they find means of escape through 

 chinks and crevices to the surface. 



We know that many trap rocks contain a portion of water and of muriatic acid, 

 and that the latter body has even been detected in the domite of Auvergne, a vol- 

 canic production, which, comparatively speaking, must be regarded as of extreme 

 antiquity* ; so that we may more readily conceive, in what manner lavas of recent 

 origin retain larger quantities of the same volatile principles, and even certain saline 

 substances, diffused through their pores and fissures. 



Perhaps indeed, although chemical attraction in these cases is out of the question, 

 a certain degree of adhesive affinity may have been exerted, between the substances 

 exhaled, and the walls of the cavities that had contained them. Dr. Faraday, in the 

 Sixth Series of his Researches on Electricity, published in our Transactions, has in- 

 troduced some pertinent remarks on this kind of influence, referring to it, amongst 

 other phenomena, the operation of platina in determining the union of oxygen and 

 hydrogen in Dobereiner's experiment. Nor indeed does it seem improbable, that, as 

 heat exercises a repulsive power, not only between the particles of bodies, but like- 

 wise between masses of them-}-, so likewise a species of aflinity may exist between 

 masses of matter even where their particles are not mutually attractive ; and that this 

 may retard the operation of heat upon bodies possessing intrinsically a considerable 

 degree of volatility, and prevent their entire disengagement all at once from the cavi- 

 ties of the substance which entangled them. 



Be that as it may, it seems certain from the above observations, that ammonia is 

 one of the original products of volcanic action in the case of Vesuvius ; and it 

 would be easy to extend the same inference to other volcanos, — a fact, I am aware, by 

 no means new, but still one, the circumstances of which seem to deserve investiga- 

 tion, especially, as from the readiness with which nascent hydrogen enters into com- 

 bination with azote, it might be imagined, that the ammonia was somehow or other 

 generated in the open air, owing to a disengagement of hydrogen from the lava. 



I trust, that the having traced it to the vapour directly issuing from the mass effec- 

 tually dispels such a suspicion, and will serve as an additional argument in support of 

 an opinion I have long entertained, that atmospheric air and water both find their way 

 to the seat of volcanic operations, and are alike deprived of their oxygen by certain 

 principles there existing ; whilst the residuary nitrogen and hydrogen are evolved, in 

 in some cases separately, in others united, in the form of ammonia. 



* I might likewise refer to the existence of carburetted hydrogen in a condensed state in cavities of rock- 

 salt at Wielitzka, and that of sal ammoniac in that of the Tyrol, as facts of the same description. The latter 

 might lead to some speculations with regard to the origin of sea-salt, to which I may perhaps on some future 



occasion recur. 



t See Professor Powell's Paper in the Philosophical Transactions for 1834, Part II. 



