Sturgis listened with deep attention to his friend's narrative, and ruminated in silence long after the artist had ceased speaking. At last he started up with a sudden exclamation, and walking over to the side of the tank, he looked into the depths of its oily contents, as if fascinated by some horrible thing he saw there. Sprague came and stood beside him and gazed curiously into the viscous liquid. There was nothing there that he could see. "What is it?" he asked. Without replying, Sturgis took from his pocket a bone-handled knife and carefully dipped one end of the handle into the fluid in the leaden tank. At once the liquid began to seethe and boil, giving out dark pungent fumes. "I thought so," muttered the reporter, under his breath; "that man is truly a genius--the genius of evil." "Who?" asked Sprague. Sturgis made no reply. His eyes were wandering about the room, as if in search of something. "Hand me a couple of those long glass tubes from that shelf yonder," he said, earnestly. The artist complied with the request. Dipping these tubes into the oily liquid, Sturgis, after considerable difficulty, managed to seize with them a small dark object which lay at the bottom of the tank. With infinite precaution, he brought it to the surface. It had the appearance of a flattened leaden bullet. "What is it?" inquired Sprague. "Sit down," answered Sturgis, in a low, tense voice. "I have just found the last link which completes my chain of evidence; I am now prepared to tell you such a story as you will scarcely credit, even with the absolute proofs before your eyes." CHAPTER XX. THE LEAD-LINED VAT. Sprague seated himself upon the long pine box; and Sturgis, dropping into the only chair, began his narrative. As he talked, he carelessly whittled the cover of the wooden box with the knife which he still held in his hand. He began with an account of his investigation at the Knickerbocker bank, and explained the result of his observations and inferences down to the time of his visit to Murdock's house, omitting, however, to mention any of the names of the actors in the reconstructed drama.