“Watch those pumps. They’re putting air under great pressure. That makes it cold. When it’s just so cold, I run it over pipes full of more air. That makes air number two pretty cold. I put air number two under great pressure. Then it is cold enough to turn into a liquid, part of it. It drips off just as condensed steam does.”
“And so-o,” Johnny drawled, “you get liquid air. How much is it worth?”
“From fifty cents to one dollar a quart.”
“Whew!” Johnny whistled. “High priced air I’d say.”
He dropped into a chair. “So that’s how your grandfather got something valuable out of nothing but the sky! Gold from the sky!” Johnny chuckled.
“But say!” he was on his feet again. “Who wants the stuff? What’s it good for?”
“Well,” replied Donald after turning a valve and setting one more pump hissing, “men go about the country lecturing on liquid air, freezing up tennis balls so hard they crack on the floor like an egg shell, making tuning forks out of lead by freezing it up, all that. They buy liquid air.
“Big mills that manufacture locomotives use liquid air. They freeze up whole engine wheels with liquid air, then put on the tires, which are not frozen. When the wheel thaws out it expands and there you have your tire on tight as a drum. Funny business isn’t it?
“But mostly,” he slid another jug into position, “liquid air is split up before it’s used.”
“Split up?” Johnny stared.