t^ On t>M ^ligin ofMeteonc Atones- 



carboD, and yet it assumes the elastic fofna in carbonic acid 

 and carbureted hydrogen gas. In like manner, sulphur in sul- 

 phuric acid and in sulphuretted hydrogen gas, silica in fluoric 

 acid gas, and so of others. Fewer examples can, indeed, be 

 given of metals ; it is, however, known that, in distilling muria- 

 tic acid over clay containing iron, at all times a portion of iron 

 is carried over it. The particles of iron are, indeed, in this case, 

 generally regarded as mechanically suspended ; but I cannot 

 comprehend why muriatic acid gas, in other respects so power- 

 ful, should not be equally efficient in dissolving oxide of iron 

 as the acid in its fluid state. In short, it is to be apprehended, 

 that the solvent powers of the acid gases have not hitherto been 

 sufficiently ascertained : it is more than probable, that they act 

 both on the metals and metallic oxides. Some chemists, indeed, 

 have observed that even hydrogen gas dissolves a portion of 

 iron. 



' Be that as it may, there are not wanting other indications 

 that even the metals, and that, too, at the usual temperature, 

 can assume the aerial or gaseous form. That metals raised to 

 an extreme degree of heat can be volatilized, is a fact, and shews 

 at least, in general, their susceptibility of volatilization. But 

 that they are also subject to it, however inconsiderable in degree, 

 at the ordinary temperature, their smell appear to me unequivo- 

 cally to determine ; and the green hue assumed by copper in 

 combustion cannot well be explained otherwise than by the dif- 

 fusion of a fine metallic vapour. 



Evaporation may perhaps be assumed as the general law 

 of all bodies whatever. That all fluid bodies, without ex- 

 ception, evaporate, is undoubted ; but with respect to solids 

 this is more obscure. However, the same reason applies, as in 

 the case of metals, to all bodies which emit a peculiar odour. I 

 may here also appeal to a common phenomenon, which is indeed 

 usually differently explained, but which may at least deserve a 

 fiiore attentive consideration. Every one knows that in a well 

 closed room, or press, a quantity of dust in time accumulates. 

 Even within a watch, fitted with the utmost nicety^ particles of 

 dust shew themselves from time to time, both in the interior and 

 on the dial-plate. Whence is this ? It is generally explained, 

 without farther investigation, by the entrance of extremely fine 

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