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the part of Solfatara which is formed by this tufa, has once made a part of the bottom of the sea, and been thrown up by the action of submarine fires. Nor is it improbable that the rest of it has had the same origin, and that all the substances of this volcano have issued froin the waters of the sea. Such we know to have been the origin of many other mountains, either now actually burning, or which have ceased to burn.

It is well known that, for a long time, alum and sal-ammoniac have been extracted from this half-extinguished volcano. The method employed for each was as follows. In the process for the alum, certain square places were cleared out in the plain of Solfatara, in which it effioresced, and the efflorescences were swept together, and, from them, by methods well know!), the salt was collected purified. The sal-ammoniac was obtained by placing a number of pieces of tile round the apertures from which that salt issued, in the form of a subtle vapoar, upon which the vapour was condensed, A description of these two meibods is to be found in almost all the authors who have written on Solfatara; some of whom, with reason, censure them as imperfect, and consequently not likely to produce the profit which might be obtained. But we may now hope that both these manufactures

may

become objects of importance, under the direction of the Abbé Breislak, and the liberal patronage of Baron Don Giuseppe Brentano, who has taken this celebated Phlegrean field at a constant rent. The Abbé, proceeding on the principle that the quantity of alum procured from Solfatara must be proportionate to the area of the space on which it effloresces, instead of the narrow squares formerly appropriated to this purpose, and called gardens, has greatly extended the spaces allotted ; and that the preparation of this salt may not be prevented by the rain-water draining into the bottom from the steep sides of the volcano, he has surrounded them with small ditches, with deep wells at intervals, which receives the water, and where it is soon absorbed by the spongy earth. In the lower part of these sides he has likewise opened a number of cavities equally proper to furnish alum,

The same principle appears to have guided the Abbé in his attempts to increase the quantity produced of sal-ammoniac, by making use of long and capacious tubes of earth, open at both extremities, and baked in the furnace. These receive, at their lower ends, the va

pours abounding with this salt, which attaches itself to their inner sides, and forms there a crust, that in time increases to a considerable thickness. I have seen with pleasure at Naples the effects of these two methods; and it is expected they will be still more productive, when some alterations suggested by persons well acquainted with this business have been made.

Forinerly sulphur was extracted from the crater of this volcano; but the small quantity of it, and the low price of the commodity, have caused this labour to be abandoned.

[Spalanzani.]

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END OF VOL. I.

R. Wilks, Printer, 89, Chancery-lane.

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