“But that’s clear water,” said Tom.
“Yes, clear distilled water, but not alone. It contains a great deal of silver.”
“Whereabouts, lecturer?” said the Vicar.
“In solution,” said Uncle Richard gravely. “Here we have one of the wonders of science laboriously worked out by experiment, and when discovered simplicity itself. Tom, suppose I take a piece of bright clear iron and leave it out exposed to all weathers, what happens?”
“Gets rusty,” said Tom.
“Exactly; and what is rust?”
“Red,” said Tom.
“So is your face, Tom, for giving so absurd an answer.”
“Yes, uncle,” said Tom frankly. “I don’t quite know.”
“Oxide of iron,” said the Vicar.