VI
The Detectaphone
FAR after midnight though it had been when we had at last turned in at our apartment, Kennedy was up even earlier than usual in the morning. I found him engrossed in work at the laboratory.
"Just in time to see whether I'm right in my guess about the illness of Brixton," he remarked, scarcely looking up at me.
He had taken a flask with a rubber stopper. Through one hole in it was fitted a long funnel; through another ran a glass tube, connecting with a large U-shaped drying-tube filled with calcium chloride, which in turn connected with a long open tube with an up-turned end.
Into the flask Craig dropped some pure granulated zinc coated with platinum. Then he covered it with dilute sulphuric acid through the funnel tube. "That forms hydrogen gas," he explained, "which passes through the drying-tube and the ignition-tube. Wait a moment until all the air is expelled from the tubes."
He lighted a match and touched it to the open upturned end. The hydrogen, now escaping freely, was ignited with a pale-blue flame.
Next, he took the little piece of wall-paper I had seen him tear off in the den, scraped off some powder
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