"I'd do anything you asked me to," said the inventor.
"Then never forget," said Simon deliberately, "that I was with you the whole of this morning — from half past ten till one o'clock. That might be rather important." Simon lighted a cigarette ajid stretched himself luxuriously in his chair. "And when you've got that thoroughly settled into your memory, let us try to imagine what Augustus Parnock is doing right now."
It was at that precise moment, as a matter of history, that Mr. Augustus Parnock and his friend who understood those things were staring at a brass ashtray on which no vestige of plating was visible.
"What's the joke, Gus?" demanded Mr. Parnock's friend at length.
"I tell you it isn't a joke!" yelped Mr. Parnock. "That ashtray was perfectly plated all over when I put it in my pocket at lunchtime. The fellow gave me his formula and everything. Look — here it is!"
The friend who understood those things, studied the scrap of paper, and dabbed a stained forefinger on the various items.
"Cu is copper," he said. "Hg is mercury and HNO 3, is nitric acid. What it means is that you dissolve a little mercury in some weak nitric acid; and when you put it on copper the nitric acid eats a little of the copper, and the mercury forms an amalgam. CuHgNO 3 is the amalgam — it'd have a silvery look which might make you think the thing had been plated. The other constituents resolve themselves in H 2 O, which is water, and NO 2, which is a gas. Of course, the nitric acid goes on eating, and after a time it destroys the amalgam and the thing looks like copper again. That's all there is to it."
"But what about the St?" asked Mr. Parnock querulously. His friend shrugged.
"I can't make that out at all — it isn't any chemical symbol," he said; but it dawned on Mr. Parnock later.