288 ANNUAL OF SCIENTIFIC DISCOVERY. 



its bottom. Its activity at present is confined to the emission of 

 vapor, and even this seems at times, when viewed from the sea, to 

 be wanting. On the summit, however, these vapors appear dense 

 enough, and are sufficient to prevent the possibility of making the en- 

 tire circuit of the crater. The observer is much struck, not only with 

 the change of form in the summit, as shown by the drawings of Prof. 

 Scacchi, but also with the sharpness of the lip of both craters, which 

 is such that it is hardly possible for more than two persons to stand 

 abreast upon it. During the late eruption, the lava found vent from 

 the base of the cone, on a level with the sand plain which fills the 

 ancient crater of Somma. It here poured out a torrent of scoriaceous red 

 lava through a well defined canal. This is now entirely cold, and we 

 collected from its sides abundant specimens of aphthitalite, which 

 frosted over the rugged cavern like snow. Near this spot also are two 

 fumeroles formed during the last eruption ; the largest about 25 feet 

 high, with an aperture of near ten feet, its outer walls black, rugged 

 and forbidding. The flow of lava from the eruption of 1849 was in the 

 direction of the ancient Pompeii, and it was copious enough to destroy 

 a small village, with its vineyards, at the distance of several miles. 

 Prof. B. SiUiman; Notes on Europe. Silliman's Journal. 



ON THE RESULTS OF THE LATEST RESEARCHES EXPLANATORY OP CAR- 

 BONIC ACID EXHALATIONS. 



BISCHOFF found that carbonic acid was gradually separated from car- 

 bonate of lime by silicic acid with the cooperation of boiling water. 

 This decomposition took place, whether the silicic acid was in a solu- 

 ble or insoluble condition ; for even finely pulverized quartz decomposed 

 the carbonate of lime, the process in that case being rather slower. 

 Carbonate of iron and the carbonate of magnesia behave in like manner ; 

 the latter is decomposed even more easily and in greater quantity than 

 the carbonate of lime. The more facile decomposition of carbonate of 

 magnesia is shown by the fact that even boiling water by itself separ- 

 ates the carbonic acid from it, this not being the case with the car- 

 bonate of iron. When, therefore, either limestone, dolomite, or sparry 

 iron, occurs at a depth beneath the earth's surface where boiling water 

 heat exists and water has access, carbonic acid will be driven off from 

 these carbonated salts. The Soffoni in Tuscany, discharging boiling hot 

 water from crevices in limestone, must come from a depth where boil- 

 ing heat exists, and it is very probable that the accompanying carbonic 

 acid arises from the above-mentioned causes. The same must be ad- 

 mitted for the carbonic acid discharged so abundantly in the neighbor- 

 hood of ancient localities of volcanic action in various parts of central Eu- 

 rope. According to the laws of the increase of temperature towards the 

 centre of the earth, we may calculate that boiling heat exists at a depth 

 of about 8600 feet in these districts, and this depth is certainly within 

 the limits of the clay slate formation of Germany, which is calculated 

 to be at least a mile (German) thick. Calcareous beds (transition lime- 

 stone) and quartzose rocks occur at this depth ; waters penetrate thereto, 

 and carbonic acid is separated from the limestone, as in the above-men- 



