In commerce this acid is manufactured in large quantities and by elaborate processes. The engineer had no such means at his command, but he knew that in Bohemia an acid known as Nordhausen is made by simpler means, which has, moreover, the advantage of being non-concentrated. For obtaining the acid in this way, all the engineer had to do was to calcinize the crystals in a closed jar in such a manner that the sulphuric acid distilled in vapor, which would in turn produce the acid by condensation. It was for this that the refractory jars and the furnace had been made. The operation was a success; and on the 20th of May, twelve days after having begun, Smith was the possessor of the agent which he expected to use later in different ways. What did he want with it now? Simply to produce nitric acid, which was perfectly easy, since the saltpetre, attacked by the sulphuric acid, would give it by distillation. But how would he use this acid? None of the others knew, as he had spoken no word on the subject. The work approached completion, and one more operation would procure the substance which had required all this labor. The engineer mixed the nitric acid with the glycerine, which latter had been previously concentrated by evaporation in a water-bath, and without employing any freezing mixture, obtained many pints of an oily yellow liquid. This last operation Smith had conducted alone, at some distance from the Chimneys, as he feared an explosion, and when he returned, with a flagon of this liquid, to his friends, he simply said:—“Here is some nitro-glycerine!” It was, in truth, that terrible product, whose explosive power is, perhaps, ten times as great as that of gunpowder, and which has caused so many accidents! Although, since means have been found of transforming it into dynamite, that is, of mixing it with clay or sugar or some solid substance sufficiently porous to hold it, the dangerous liquid can be used with more safety. But dynamite was not known when the colonists were at work on Lincoln Island. “And is that stuff going to blow up the rocks?” asked Pencroff, incredulously. “Yes, my friend,” answered the engineer, “and it will do all the better since the granite is very hard and will oppose more resistance to the explosion.” “And when will we see all this, sir?” “To-morrow,” when we have drilled a hole,” answered the engineer. Early the next morning, the 21st of May, the miners betook themselves to a point which formed the east bank of Lake Grant, not more than 500 feet from the coast. At this place the plateau was lower than the lake, which was upheld by the coping of granite. It was plain that could they break this the waters would escape by this vent, and, forming a stream, flow over the inclined surface of the plateau, and be precipitated in a waterfall over the cliff on to the shore. Consequently, there would be a general lowering of the lake, and the orifice of the water would be uncovered—this was to be the result.