Old Stone agreed to the deal, but the expression on his face clearly said, "I'll believe it when I see it."
Gu Xiuyuan didn't mind. He walked to the pile of ore, crouched down, and carefully examined them. The piece with the highest iron content that he'd scanned with his elemental vision was set aside. He picked out a few more pieces of different grades, forming a small pile.
Old Stone came over, watching him pick and choose, unable to resist asking, "What are you picking those for?"
"To run experiments," Gu Xiuyuan said without looking up. "Need different purity grades for comparison."
"Comparison?" Old Stone didn't understand.
Gu Xiuyuan didn't explain, just asked, "Do you have any containers? Ones that can hold water. And a heat source."
Old Stone paused for a moment, then rummaged from a corner and produced a cracked old pottery jar, a few stone bowls, and a flint.
"That's all," he said. "This old man usually uses true fire, don't need these things."
Gu Xiuyuan took the pottery jar and examined it. It was old, with a layer of black grime inside, but still usable. The stone bowls were clean, probably what Old Stone usually ate from.
He asked again, "Is there water?"
Old Stone pointed to a corner of the cave, where there was a shallow depression holding a pool of clear water. The water seeped from rock crevices, very clear, but with a faint sulfur smell.
Gu Xiuyuan went over, cupped some in his hand, and tasted it. The flavor was unpleasant, but usable.
He returned to the stone table, placed the high-iron ore on it, and pulled a small cloth bundle from his pocket.
Old Stone curiously came closer to look.
The bundle contained several small glass bottles and some things he'd never seen before. Gu Xiuyuan carefully took out one bottle containing a transparent liquid. This was the concentrated sulfuric acid he'd brought from the lab, originally for cleaning scale, casually stuffed into his bag, now becoming his "secret weapon" in this alien world. The bottle held about 100 milliliters, enough for several purification experiments, but every drop would have to be used sparingly.
"What's this?" Old Stone asked.
"Sulfuric acid," Gu Xiuyuan said. "Brought from Earth."
Old Stone naturally didn't know where "Earth" was, nor what "sulfuric acid" was. But seeing Gu Xiuyuan's serious expression, he didn't ask further.
Gu Xiuyuan smashed the ore and ground it to powder in a stone bowl. The process was laborious; the ore was hard, requiring several strikes to break. The powder was uneven, so he repeatedly ground it with a flat stone until it was fine.
Old Stone watched from the side, increasingly confused.
"What... what are you doing?" he couldn't help asking.
Gu Xiuyuan didn't answer, focusing on the next step. He poured the ore powder into the pottery jar, added appropriate water, and stirred with a wooden stick. The water in the jar quickly became turbid, taking on a dark red color.
"Why is the water turning red?" Old Stone exclaimed in surprise.
"Iron dissolving," Gu Xiuyuan said. "Or rather, some iron compounds dissolving."
Old Stone didn't understand, but he stopped asking, just watched wide-eyed.
Gu Xiuyuan placed the pottery jar on the fire and started heating. Flames licked the bottom, the liquid inside slowly steaming. He stirred while heating, occasionally pausing to observe color changes.
Old Stone crouched nearby, like a curious child.
After about a stick of incense's time, Gu Xiuyuan took the jar off the fire, letting it cool. When the temperature dropped, he carefully added a few drops of sulfuric acid.
"Sss——"
A pungent fizz of bubbles erupted, white smoke rising. Old Stone jumped back in fright.
"You, what are you doing! This is poison gas!" he shouted, covering his nose.
Gu Xiuyuan also turned away, avoiding the smoke. When it dissipated, he said, "Normal reaction. Sulfides react with sulfuric acid to produce sulfur dioxide, which is toxic. Stand back."
Old Stone quickly retreated to the cave entrance, watching from afar.
Gu Xiuyuan continued. He poured the liquid from the jar into a stone bowl, filtering it through a piece of cloth. The residue was gray-black sediment; the filtered liquid was turbid green. He discarded the residue, looking thoughtfully at the filtered liquid.
"Need precipitation," he murmured to himself.
He took another small bottle from his cloth bundle, containing white powder. This was his self-prepared sodium carbonate, used to adjust pH. He carefully added small amounts to the filtered liquid, stirring constantly.
The green liquid began to change. First, tiny bubbles emerged, then the color deepened, and finally, dark red precipitate formed.
"Iron hydroxide," Gu Xiuyuan murmured.
He stopped adding sodium carbonate, letting the precipitate slowly settle. When the top liquid became clear, he carefully poured it off, leaving the bottom precipitate. Then he added clean water, stirred, let settle, and poured off again. Repeating three times, the precipitate became pure.
Finally, he spread the precipitate on another stone slab and placed it near the fire to dry.
The entire process took nearly two hours. Old Stone had watched from the cave entrance, from initial skepticism to later surprise, and finally to utter amazement.
When Gu Xiuyuan handed him that small pile of dark red powder, his hands were trembling.
"Check the purity," Gu Xiuyuan said.
Old Stone probed with his spiritual sense, then his eyes bulged like copper bells.
"This, this..." he stammered, "purity is at least ninety percent! This old man has mined for centuries, never seen such pure ore!"
Gu Xiuyuan leaned against the cave wall, rubbing his temples. Several hours of concentrated effort, plus multiple uses of elemental vision, had consumed one-third of the Purple Flame Heart's energy. He felt tired, but inwardly satisfied.
"This is called chemical purification," he said. "Not using magic, using reactions. Turn unwanted components into gas or soluble substances, separate them out, what remains is what you need."
Old Stone looked at him, his expression completely changed.
"Master!" He suddenly bowed deeply. "Accept this old man's bow of respect!"
Gu Xiuyuan stepped aside: "No need. It's a deal as agreed. You teach me cultivation, I teach you chemistry."
Old Stone straightened up, face beaming: "Of course, of course! This old man will teach everything he knows! But Master, this word 'chemistry,' this old man has heard it for the first time. What kind of learning is this?"
Gu Xiuyuan thought for a moment, then explained in terms he might understand: "It's the study of the composition, structure, and change patterns of substances. For example, why is this ore red? Because it contains iron oxide. Why can acid remove impurities? Because impurities react with acid to form soluble substances, while iron doesn't react. These are all things chemistry studies."
Old Stone listened, half-understanding, but his eyes were full of reverence.
"Master is brilliant!" he said. "This old man has lived centuries, never seen such a method. Those artifact refiners use true fire to refine, consuming time and effort, with far less purity than Master's method. If this method of Master's spreads, the entire cultivation world would shake!"
Gu Xiuyuan shook his head: "Not looking to spread it for now. The deal between us stays between us two."
Old Stone paused, then nodded: "Understood. Master rest assured, this old man's mouth is tight."
Gu Xiuyuan didn't explain further. It wasn't that he didn't want to spread it, but he didn't know what consequences this method might bring in the cultivation world. Old Stone was right – if this method spread, it might indeed cause upheaval, but not necessarily for the better.
Old Stone rubbed his hands together and asked, "Master, when shall we begin?"
"Begin what?"
"Teaching you cultivation!" Old Stone said. "Master agreed to it."
Gu Xiuyuan nodded: "Now is fine."