Chapter 091: Dry Distillation for Acid Production

By dusk, Luo Chong had finished his laborious task—using a bronze shovel and wooden cart to strip away the topsoil around the livestock pens and latrines. The collected earth formed a sizable mound near the cave entrance, resembling an unmarked grave.

At dawn, he assigned four women to refine saltpeter. They dissolved the soil in large water vats, allowing the mixture to settle before filtering it through dried grass. The resulting liquid was then boiled down in clay pots until yellowish crystals—saltpeter—began to form.

"Chief, is this salt? How can there be salt in latrine soil?" the Elder and Lame exclaimed in astonishment. They had expected something new and remarkable from Luo Chong's latest endeavor, but they never imagined it would yield something resembling salt.

"This is not salt—it's saltpeter, and it's highly toxic. No one is to touch it," Luo Chong warned.

"What? Poisonous? Then why waste so much firewood making this stuff? I need that wood for pottery," Lame grumbled.

"I wouldn't go through the trouble if it wasn't useful. Just do as I say. Now go knead that white clay—I need to mold something later," Luo Chong instructed.

"You mean crucibles again? I already know how to make those. Let me handle it," Lame said confidently, thumping his chest.

"They are crucibles, but not the kind you're used to. Just prepare the clay—I'll handle the molding."

"Oh! New crucibles, huh? I'll get right on it." Excited at the prospect of learning something new, Lame scurried off. He had developed a fascination for burning and crafting materials.

Fire—the fundamental force that separated humanity from beasts. It enabled the cooking of food, fueling brain development and evolution. Fire allowed for pottery, bricks, glassmaking, metal smelting, and even clearing land for agriculture. Without fire, humans would still be nothing more than leaf-eating primates in the treetops.

And on this world, Luo Chong knew more about fire than anyone else.

After demonstrating the saltpeter refinement process twice, he left the women to continue and turned his focus to another crucial task.

Blasting open the salt mine wouldn't be feasible with black powder. Not only would an immense quantity be required, but he was also missing key ingredients. Saltpeter and charcoal were available, but sulfur was in short supply. Extracting it from pyrite (iron sulfide) was possible but inefficient. Instead, he opted for a different approach—to maximize explosive power with minimal resources by creating nitroglycerin.

To do this, he needed glycerin, which could be extracted from animal fat—a commodity the Han Tribe had in abundance after the winter wolf hunt. But the real challenge was obtaining nitric acid.

Nitric acid could be produced by distilling saltpeter with sulfuric acid—but without sulfuric acid, Luo Chong had to extract it from pyrite.

Pyrite wasn't pure iron sulfide; it contained carbon, silica, alumina, and sulfide compounds. To transform it into metal sulfates necessary for sulfuric acid production, it first needed to undergo a reduction reaction.

The process was straightforward—just heat it up.

However, this wasn't something he could simply throw into a furnace—unless he wanted an explosion.

Instead, Luo Chong employed an ancient technique—dry distillation kilns—similar to charcoal-making. He selected a flat area near the carbonization pit and stacked layers of pyrite in a crisscross "井" pattern, surrounding the pile with firewood. The entire structure was built into a mound and buried under a layer of dry grass, then sealed with wet clay—leaving only a few small vents at the bottom and top for airflow.

Lighting a fire beneath the pile, he initiated a slow-burning reaction. The pyrite contained both carbon and sulfur, allowing it to combust within the oxygen-controlled chamber.

This reduction process would take about two weeks, during which time the iron sulfide would convert into iron sulfate, and the alumina would transform into aluminum sulfate—both key precursors for sulfuric acid.

With the reaction underway, Luo Chong set to work crafting specialized equipment.

Equipment for Acid Refining

The key apparatus for sulfuric acid production included:

1. A distillation boiler

2. A cooling system (condenser tubes)

And as always, fire was essential.

Lame had already prepared the refractory clay, and Luo Chong immediately began shaping the necessary vessels while Lame observed carefully—though unbeknownst to him, this would be a one-time lesson. Once a single set of equipment was built, it would suffice indefinitely.

The process was simple:

• A round clay slab formed the base.

• Clay coils were layered to build a cylindrical chamber with no tapering neck—different from smelting crucibles.

• The lid was crucial. Unlike crucibles, which didn't require covers, this distillation boiler needed a tightly sealed top—with a built-in chimney-like vent.

The lid was slightly wider than the crucible's opening, ensuring a snug fit. When in use, the joint would be sealed with wet clay, allowing vapor to escape only through the vent pipe.

If it sounded familiar, that's because it was akin to a pressure cooker, except without a pressure valve.

Next came the condenser pipes, which were simple clay tubes, carefully crafted to fit the boiler vent. Several curved connectors were also molded for assembly. The most critical component was the double-layered condenser—a thin inner tube encased by a wider outer pipe.

The outer pipe was left open at the top, allowing it to be filled with cold water. This would cool the vapor passing through the inner tube, condensing it into liquid sulfuric acid.

The concept was simple—akin to sticking a straw through the middle of a water bottle, where the straw carried hot steam while the surrounding water cooled it into a liquid. Any high school physics student could grasp the principle, but Luo Chong? He was trained at a military academy.

Three complete sets of equipment were built:

1. One for sulfuric acid production

2. One for nitric acid purification

3. One for refining sodium carbonate (soda ash)

The latter was necessary because, while the tribe had collected natural soda minerals, the raw form was unusable without purification.

After molding the pieces, they were left to dry before being fired in the kiln—Lame's responsibility. Once hardened, they could be used alongside everyday ceramic wares.

Signs of Spring

With everything set in motion, Luo Chong finally had time to check on the livestock.

The wild cattle were shedding—patches of fur peeling away to reveal smooth skin underneath. Unlike water buffalo, which remained hairless year-round, these forest cattle grew thick winter coats, which they shed when spring arrived.

What a miraculous adaptation, Luo Chong mused. If only humans could grow and shed their own built-in winter coats—nature's answer to puffer jackets.

The alpacas were also shedding, though not completely bald—merely losing their thick winter undercoats. They still looked as fluffy and round as plush toys.

The rabbits were also shedding—and more importantly, over twenty were pregnant again. Truly prolific breeders.

The shedding of these animals confirmed what Luo Chong had already suspected—spring had officially arrived.

Night temperatures no longer dropped below freezing. It was time to begin planting crops.

He even considered using animal shedding cycles as an annual natural farming calendar. With no modern thermometers available, these creatures had a far better instinct for climate change than humans.

If the animals were shedding, the soil was warm enough.

It was time to sow the fields.