Beyond their knowledge of the working of metals, in which they had great facility, Zenas Wright soon found that the scientists of Nematzin could avail him little in his search for explosive compounds. Ordinary gunpowder, indeed, he knew he could make easily enough, after a fashion, but he sought for something more powerful by far than that. From the descriptions which he had heard of the Kimbrian Wall, he judged that it would be a rare task to shake it down. "We might do it with nitroglycerin," he told Everson. "But we would have to set all of the old wives of Ruthar to soap-making to get our glycerin, and it would be a difficult job to get it pure enough to serve our turn. Besides, nitroglycerin is mean and uncertain to handle." The two men sat before a ruddy coal fire in the big laboratory room which had been turned over to the uses of the geologist--a fire well screened from the rest of the room, so that no flying spark should raise mischief among the experiments of Zenas. Three weeks had elapsed since their arrival at Zele-omaz. Polaris Janess was well along the road to health. Everson and Oleric, laboring tirelessly, had established five great training camps, one on the plain near the city, and four others in the forests to the north beyond the Illia. Already the levies of Ruthar were pouring into the camps, where they were drilled by the zinds and captains, under the direction of the naval lieutenant and the red captain. Everson had thrown his whole heart into the work. Already he had made considerable progress in the learning of the Rutharian language. He was beginning to take a vast pride in the army he was welding. Born soldiers he found these Rutharians, amenable to the strict discipline which he preached, and to whom his word was law. He had ridden in this day from a tour of inspection of his camps to visit Wright and learn of the progress of the work on which depended their entire scheme of campaign. "Nitroglycerin," said Everson. "So you have found a source of nitric acid, then?" "Yes," replied Wright. "One of the first things which took my eye among a number of specimens of rock which I found in a case here, was a chunk of sodium nitrate. You know the stuff--Chile saltpeter, they call it." "Why not a picrate powder, if you have nitrates to work with?" suggested the lieutenant. "Picrate--nitric acid--phenol," said old Zenas. "That's the way of it. And to get phenol--lots of it--" He broke off and stared into the depths of the fire. "Hey!" he cried, and jumped to his feet so suddenly that Everson started. Zenas pointed at the fire, his little black eyes dancing and his beard wagging with his excitement. "Well?" queried Everson.