“Listen to me, my friends,” said the engineer, who thereupon made known the result of his observations. His theory was, that a cavity, more or less considerable, existed in the mass of granite which upheld Prospect Plateau, and he undertook to penetrate to it. To do this, it was first necessary to free the present opening, in other words to lower the level of the lake by giving the water a larger issue. To do this they must manufacture an explosive with which to make a drain in another part of the bank. It was this Smith was going to attempt to do, with the minerals Nature had placed at his disposal. All entered into the proposal with enthusiasm. Neb and Pencroff were at once detailed to extract the fat from the dugong and to preserve the flesh for food; and soon after their departure the others, carrying the hurdle, went up the shore to the vein of coal, where were to be found the schistous pyrites of which Smith had procured a specimen. The whole day was employed in bringing a quantity of these pyrites to the Chimneys, and by evening they had several tons. On the next day, the 8th of May, the engineer began his manipulations. The schistous pyrites were principally composed of carbon, of silica, of alumina, and sulphuret of iron,—these were in excess,—it was necessary to separate the sulphuret and change it into sulphate by the quickest means. The sulphate obtained, they would extract the Sulphuric acid, which was what they wanted. Sulphuric acid is one of the agents in most general use, and the industrial importance of a nation can be measured by its consumption. In the future this acid would be of use to the colonists in making candles, tanning skins, etc., but at present the engineer reserved it for another purpose. Smith chose, behind the Chimneys, a place upon which the earth was carefully levelled. On this he made a pile of branches and cut wood, on which were placed pieces of schistous pyrites leaning against each other, and then all was covered over with a thin layer of pyrites previously reduced to the size of nuts. This done, they set the wood on, fire, which in turn inflamed the schist, as it contained carbon and sulphur. Then new layers of pyrites were arranged so as to form an immense heap, surrounded with earth, and grass, with air-holes left here and there, just as is done in reducing a pile of wood to charcoal. Then they left the transformation to complete itself. It would take ten or twelve days for the sulphuret of iron and the alumina to change into sulphates, which substances were equally soluble; the others—silica, burnt carbon, and cinders—were not so. While this chemical process was accomplishing itself, Smith employed his companions upon other branches of the work, which they undertook with the utmost zeal.