Site of the Ancient City of the Aurunci. 255 



advance no higher claim than that of being a plausible conjecture. 

 The general occurrence of volcanoes in the neighbourhood of the sea, 

 and the constant disengagement of aqueous vapour and of sea-salt 

 from their interior, are facts, which establish in my mind a convic- 

 tion that water finds its way to the seat of the igneous operations, 

 almost as complete as if I were myself an eyewitness of another 

 Phlegethon discharging itself into the bowels of the earth, in every 

 volcanic district, as in the solitary case of Cephalonia. 



•* Nor is the access of atmospheric air to volcanoes more question- 

 able than that of water ; so that the appearance of hydrogen united 

 with sulphur, and of nitrogen, either alone or combined with hydro- 

 gen, at the mouth of the volcano, seems a direct proof that oxygen 

 has been abstracted, by some process or other, from both. 



*' Having satisfied our minds with regard to the fact of internal 

 oxidation, we naturally turn to consider what principles can have 

 existed, in the interior of the earth, capable of extracting oxygen 

 from water as well as from air ; and this leads us to speculate on the 

 bases of the earths and alkalies as having caused it. But in ascrib- 

 ing the phenomena to the oxidation of these bodies, we ought not to 

 lose sight of the Baconian maxim, that, in every well-established 

 theory, the cause assigned should be not only competent to explain 

 the phenomena, but also known to have a real existence ; which lat- 

 ter circumstance cannot, of course, be affirmed of the alkaline and 

 earthy metalloids, as occurring in the mterior of the earth." 



Miscellaneous Observations, chiefly Chemical. By John Davf, 

 M.D., F.R.S., Lond. and Edin., Inspector-General of Army 

 Hospitals. Communicated by the Author. 



1. In experimenting upon a siliceous sand from Mabaica, 

 in British Guiana, coloured reddish-brown by peroxide of iron, 

 I perceived that it was rendered almost black by the applica- 

 tion of heat, even of a moderate degree. The effect was well 

 shewn by heating the sand either on a thin plate of glass or 

 in a platina capsule. The change of colour was distinct, when 

 the temperature, it may be conjectured, was very little above 

 the boiling point of water, and seemed to be at its maximum 

 before it attained a dull-red heat. On placing the heated 

 capsule suddenly in water, so as to reduce its temperature 

 rapidly, a rapid lightening or brightening of the colour ap- 

 peared, making a pretty experiment. 



The peroxide of iron, colouring the sand, was in the state 



