The Problem of the Green Capsule by John Dickson Carr Page B

stared, bending closer, and Elliot joined him. There, true enough, was the small brass key in the back of the clock. But where the other pin or spindle should have been there was only a tiny round hole.
    “It’s been broken off,” said Elliot, “and broken off inside the outer case of the clock.”
    He bent closer. Inside the microscopic hole he could just see a microscopic bright stump, and there was a fresh scratch round the hole on the somewhat grimy metal back of the clock.
    “It’s been damaged recently,” he explained. “That’s probably what Miss Wills meant when she said she was certain the clock was right. You see, sir? Until a clockmaker gets at this, nobody can alter the position of the hands even if he tries to.”
    Major Crow stared at it.
    “Nonsense,” he said. “Nothing easier. Like this——”
    He turned the clock round again with its face outwards. Opening the round glass door protecting the face of the clock, he laid hold of the hands.
    “All you’ve got to do,” he continued, “is simply push——”
    “Steady on, sir ! ” said Elliot.
    Even Major Crow left off, and knew himself beaten. The metal hands were too delicate. To attempt to push them in either direction was only to bend them in half or break them off; quite plainly, their position could not be altered by the fraction of a second. Elliot stood back. He began to grin in spite of himself. The hands continued their derisive course, the metal screw holding them fast winked back at him, and the ticking of the clock touched in him such a deep inner chord of amusement that he almost laughed in the Chief Constable’s face. Here was a symbol. He was looking at the fiction-writer’s nightmare—a clock that could not be tampered with.
    “So that’s that,” he said.
    “That is not that,” said Major Crow.
    “But, sir——”
    “There is some jiggery-pokery about that clock,” declared the other, with such slow and measured emphasis that he seemed to be making a vow. “I admit I don’t know what it is. But you’ll see it proved before we’re many hours older.”
    It was at this point that the Photoflood bulb, after flaring up with a dense and smoky glare, abruptly burned itself out. It startled them all, and the green-shaded lamp over in the corner now seemed dusky by contrast. But Dr. West had already drawn back; he was an elderly man with a pince-nez, who looked tired.
    “What would you like me to tell you about this?” he said to Major Crow.
    “Well, what killed him?”
    “It is prussic acid or one of the cyanides. I will do a postmortem in the morning and let you know.”
    “‘One of the cyanides?’ Joe Chesney said it was cyanide.”
    Dr. West looked apologetic. “You are probably thinking of potassium cyanide. That is one of a group of cyanide salts derived from prussic acid. But I agree it is the most common.”
    “Let me acknowledge my ignorance,” said Major Crow. “I read up on strychnine for that other business, but I’m out of my depth here. Well, say someone killed Chesney with prussic acid or its cyanide derivatives. Where does the stuff come from? How would you go about getting it?”
    “I have some notes here,” the doctor told him, fumbling in his pocket with what can only be called a sort of slow hurry. He spoke with modest satisfaction. “It’s not often we get the opportunity to see a case of prussic-acid poisoning, you know. It is rare, very rare. I made some notes in the case of Billy Owens, and I thought I had better bring them along.”
    He went on in his grateful way:
    “Pure prussic acid (HCN) is almost inaccessible to the layman. On the other hand, any good chemist could easily prepare it from non-poisonous (I mean unscheduled, not on the poison-list) substances. Its salt, potassium cyanide, is used in a variety of ways. It is used in photography, as you probably know. It is sometimes used as an insecticide on fruit trees——”
    “Fruit trees,” muttered Major Crow.
    “It is