“That’s exactly what we want you to do,” said Mr. Newton. “Can you do it now?” “Oh, I s’pose I can,” was the answer. “I can neglect all my other work to do something that will turn out to be a terrible murder, a mysterious shooting, a horrible suicide, a forgery, a child-stealing, an attempt at arson, or something worse. I can do it, I s’pose, to please you, but——” “You will do it,” said Mr. Newton, with a laugh. “I know you’re as anxious to know what made those blue spots as I am. You’re going to find out, too.” “Yes, I am,” said Mr. Hosfer, suddenly. “I wouldn’t do it for anyone else, but you’ve done me a number of favors, Mr. Newton, and I’d like to oblige you. Come into the laboratory.” Followed by Larry, Mr. Newton accompanied Mr. Hosfer. The laboratory was in the rear of the house. It was a place well filled with all sorts of queer apparatus. There were rows of bottles containing oddly-colored liquids and solids, big flasks, small furnaces, pipes, odd machines, scales, an electrical apparatus, test tubes, alembics, retorts, crucibles, and all that goes to make up a chemist’s workshop. “Now after I start to work,” said Mr. Hosfer, “I don’t want either of you to ask me a question. It bothers me, and I can’t think. When I get through you may talk all you please.” Without more ado he started in. He tore off a small piece of the paper, and put it to soak in a tube which contained some liquid. Another piece he placed in another tube. One piece he burned, and saved the ashes from it on a tiny dish. Still another piece he covered with some white substance. All the while he kept muttering to himself, like some old philosopher in search of the secret of transmuting base metals into gold. After a little while he took up the tube in which he had placed the piece of blue paper. He poured into it a few drops of some liquid, and the stuff in the tube changed color. “Ah, I thought so,” muttered Mr. Hosfer. He rapidly made a number of other experiments, going through similar performances. He tested the ashes of the paper he had burned, and even applied a small portion of them to his tongue, making a wry face as he did so. “We are coming on,” he murmured, nodding his head at Mr. Newton and Larry. “We shall be there presently.” Mindful of the injunction neither of the reporters spoke. They watched Mr. Hosfer with interest. Finally the experiments were over. The chemist holding a test tube, in which was some violet-colored liquid, came toward them. “Are you ready to hear what I have to say?” “Say on,” spoke Mr. Newton, in half tragic tones. “Whatever else that paper may have had on it, and I have not gone far enough to say all the things that were on it, that paper contained nitric acid in some form.” “Are you sure of that?” asked Mr. Newton. “Positively,” replied Mr. Hosfer.