large, but through many and smaller passages, distributed throughout the thickness of the upper part of the cone.
Second.—That some of these passages communicate with the loose cover of ashes and stones which envelopes the rocky support of the cone.
Although I have mentioned some facts which seem to indicate the existence of such favorable conditions, and which are moreover strengthened by an observation by Captain Campbell, who saw vapour issuing, and sulphur being deposited near a rocky shoulder about two-thirds of the height on the eastern descent of the cone, still their presence can only be ascertained satisfactorily by experimental digging.
The Solfatara at Puzuoli, near Naples, is a similar instance of the production of sulphur. It is a crater in which exhalations of watery vapour, sulphurous acid and hydrochloric acid take place, and where sulphur is also deposited. The sulphur is gained there by distilling it out the sand of the crater, to a depth of 10 metres or 32 feet—it becomes too hot lower down—and returning the sand which after 25 or 30 years is again charged with sulphur. The permanency of the volcano of Barren Island as a source of sulphur would depend on the rapidity with which the sulphur would be replaced after the sand had been once exhausted. The time required for this is not necessarily fixed to periods of 25 or 30 years. In Iceland, at a similar spot, the sulphur is renewed every two or three years.
If a preliminary experiment should make it appear advantageous to work the cone regularly, the material about the apex, after being exhausted of the sulphur that is present, could by blasting and other operations be disposed in such a way as to direct the jets of vapour in the most convenient manner through uncharged portions of ground. If the sulphur should aggregate in periods of not too long duration, it would be possible to carry on the work of filling up new ground on one side, and taking away saturated earth on the other at the same time, so that after working round the whole circumference, the earth that had been first put on would be ready to be taken away.
If the periods should prove too long to allow the work permanently to be carried on, an interval of time might be allowed to pass, before resuming operations.
c
