“Look here,” he said, and seizing a scrap of paper, he drew the two sketches which I reproduce. “The flask is divided down the middle by a diaphragm _C_, so as to form two chambers, _A_ and _B_. In these chambers are put two liquids, of which one is drugged and the other isn’t. _E_ and _F_ are two half diaphragms, and _D_ is a very light and delicately fitted flap valve which will close the passage to either chamber. When you invert the flask, the liquid in the upper or _B_ chamber runs out along diaphragm _C_, and its weight turns over valve _D_ so that the passage to _A_ chamber is closed. The liquid from _B_ then pours out in the ordinary way. The liquid in _A_, however, cannot escape, because it is caught by the diaphragm _F_. If you want to pour out the liquid from _A_ you simply turn the flask upside down, when the conditions as to the two liquids are reversed. You probably didn’t notice that I used the flask in this way at our lunch. You may remember that I poured out your liqueur first—it was drugged, of course. Then I got a convenient fit of coughing. That gave me an excuse to set down the flask and pick it up again, but when I picked it up I was careful to do so by the other side, so that undrugged liqueur poured into my own cup. I drank my coffee at once to reassure you. Simple, wasn’t it?” “More than simple,” Cheyne answered with unwilling admiration in his tone. “A dangerous toy, but I admit, deuced ingenious. But I don’t follow even yet. That would have left the drugged remains in the cup.” “Quite so, but you have forgotten my other two bottles and my cloth. I poured the dregs from your cup into the empty bottle, washed the cup with water from the other, wiped it with my cloth, poured out another cup of coffee and drank it, leaving harmless grounds for any inquisitive analyst to experiment with.” “By Jove!” said Cheyne, then adding regretfully: “If we had only tried the handle of the cup for fingerprints!” “I put gloves on after you went over.” Cheyne smiled. “You deserved to succeed,” he admitted ruefully. “I succeeded in drugging you,” Blessington answered, “but I did not succeed in getting what I wanted. Now, Mr. Cheyne, you would like to see the tracing. Show it to him, Dangle, while I go back to the other house for Miss Merrill.”