holding up his hands. "Stop it, Tom!" he pleaded. You'll give me a headache with all those big words."
"Oh, they're easy, once you get used to them," said the young inventor, with a smile. "Perhaps it will be easier if I say that sometimes selenium is found in native sulphur. Selenium is usually obtained from the flue-dust or chamber deposits of some factory where sulphuric acid is made. They take this dust and treat it with acids until they get the pure selenium. Sometimes selenium comes in crystal forms, and again it is combined with various metals for different uses.
"There's one good thing about it. There are several varieties, and I'll try them all before I give up."
"That's the way to talk!" cried Ned. "Never say die! Don't give up the ship, and all that. But, Tom, what you need now is a little fun. You've been poking away at this too long. Come on out on the lake, and have a ride in the motor boat. It will do you good. It will do me good. I'm a bit rusty myself—been working hard lately. Come on—let's go out on the lake."
"I believe I will!" exclaimed Tom, after thinking it over for a moment. "I need a little
