Hardwick computed dizzily on his fingers. A more complex instrument was actually needed, of course. One does not calculate on one's fingers just how long a one per cent solution of ship-fuel in frozen brine has taken to melt, and how completely it has diffused through an upside-down swamp with the pressure of forty feet of soil on top of it, and therefore its effective concentration and dispersal underground.
"I think," said Hardwick, "it's all right. By the way, did they turn the irrigation systems hind end to?"
Young Barnes did not know what this was all about. He had to send for information. Meanwhile he solicitously plied Hardwick with coffee and food. Hardwick grew reflective.
"Queer," he said. "You think of the damage forty tons of ship-fuel can do. Setting off the rest of the store and all. But even by itself it rates some thousands of tons of TNT. I wonder what TNT was, before it became a ton-measure of energy? You think of it exploding in one place, and it's appalling! But think of all that same amount of energy applied to square miles of upside-down swamp. Hundreds or thousands of miles of upside-down swamp. D'you know, lieutenant, on Soris II we pumped a ship-fuel solution onto a swamp we wanted to drain? Flooded it, and let it soak until a day came with a nice, strong, steady wind."
"Yes, sir," said Barnes respectfully.
"Then we detonated it. We didn't have a one per cent solution. It was more like a thousandth of one per cent solution. Nobody's ever measured the speed of propagation of an explosion in ship-fuel, dry. But it's been measured in dilute solution. It isn't the speed of sound. It's lower. It's purely a temperature-phenomenon. In water, at any dilution, ship-fuel goes off just barely below the boiling-point of water. It doesn't detonate from shock when it's diluted enough to be all ionized—but that takes a hell of a lot of dilution. Have you got some more coffee?"
"Yes, sir," said Barnes. "Coming up, sir."
"We floated ship-fuel solution over that swamp, Barnes, and let it stand. It has a high diffusion-rate. It went down into the mud—And there came a day when the wind was right. I dumped a red-hot iron bar into the swamp water that had ship-fuel in solution. It was the weirdest sight you ever saw!"
Barnes served him more coffee. And Hardwick sipped it, and it burned his tongue.
"It went up in steam," he said. "The swamp water that had the ship-fuel dissolved in it. It didn't explode, as a mass. They told me later that it propagated at hundreds of feet per second only. They could see the wall of steam go marching across the swamp. Not even high-pressure steam. There was a whoosh! and a cloud of steam half a mile high that the wind carried away. And all the surface water in the swamp was gone, and all the swamp-vegetation parboiled and dead. So"—he yawned suddenly—"we had a ten-mile by fifty-mile stretch of arable ground ready for the coming colonists."