“I have it, I guess. I should have guessed long ago. It’s oxygen.”
“What’s so obvious about that? Or, for that matter, why shouldn’t it be?”
“To the latter question, no reason. I simply rejected it as a possibility at first because it’s so active. I never stopped to think that it’s little if any more active at that temperature than sulfur is at ours. It’s perfectly possible to have it free in an atmosphere — provided there’s a process constantly replacing what goes into combination. You need the same for sulfur. Blast it, the two elements are so much alike! I should have thought of that right away!”
“What do you mean — a replacement process?”
“You know we breath sulfur and form sulfides with our metabolic processes. Mineral-eating life such as most plants, on the other hand, breaks down the sulfides and releases free sulfur, using solar energy for the purpose. Probably there is a similar division of life forms on this planet — one forming oxides and the other breaking them down. Now that I think of it, I believe there are some micro-organisms on Sarr that use oxygen instead of sulfur.”
“Is it pure oxygen?”
“No — only about a fifth or less. You remember how quickly the sodium and magnesium went out, and what the pressure drop was with them.”
“No, I don’t, and I can’t say that it means much to me anyway, but I’ll take your word for it. What else is there in the atmosphere? The titanium took about all of it, I do remember.”
“Right. It’s either nitrogen or some of its oxides — I can’t tell which without better controlled samples for quantity measurement. The only titanium compounds I could find in that mess were oxides and nitrides, though. The carbon oxidized, I guess — the reason there was no pressure change except that due to heat was that the principal oxide of carbon has two atoms of oxygen, and there is therefore no volume change. I should have thought of that, too.”
“I’ll have to take your word for that, too, I guess. All we have to do, then, is cook up a four-to-one mixture of nitrogen and oxygen and fill the caves the boss mentioned to about two-thirds normal pressure with it?”