The summary above says what has to happen. This says how, with the numbers that decide whether it works.
1 · Build the safety practice before the plant
Acid burns disfigure and blind, and there is no medical recovery from a serious eye exposure at this tier. Before any acid is made:
- Eye protection worn by everyone in the room, always.
- Running water within a few steps — a tank with a tap at head height — for flushing.
- Ventilation or outdoor work: sulphur dioxide and nitrogen oxides cause serious lung injury.
- Nobody works alone.
- Acids stored in glass or glazed stoneware, below eye level, and away from alkalis and anything that burns.
Acid on skin or in eyes: flush with running water for at least 20 minutes. Do not neutralise on the body.
✓ Check: Eye protection, a flushing water supply and a second person are present before any acid work begins, every time.
2 · Get sulphur
Native sulphur from volcanic and some sedimentary deposits is yellow, soft, and burns with a blue flame and a choking smell. Iron pyrite — fool's gold, brassy cubes much harder than gold — is common and gives sulphur dioxide directly when roasted.
Pyrite roasting releases large volumes of sulphur dioxide: do it in a closed flue that feeds the acid process, never in open air near people. The iron oxide left behind is useful ore — see smelting.
✓ Check: The sulphur source is identified — a sample burns with a blue flame and a choking smell, or pyrite roasting gives a sharp sulphurous gas inside a flue.
3 · Learn at bell-jar scale first
Burn a little sulphur mixed with saltpetre in a dish floating on water, under a large glass bell or jar. The nitre supplies oxygen and nitrogen oxides that carry the sulphur dioxide on to sulphuric acid, which dissolves in the water below. Repeat many times with the same water to build strength.
Small, slow, and enough to learn the chemistry, the handling and the hazards before anything is scaled up. Scaling up before the small version is reliably understood is a named failure of this step.
✓ Check: Water under the bell has become acidic enough to turn red-cabbage indicator red and to dissolve a scrap of iron with bubbling.
4 · Scale up with a lead chamber
A large chamber lined with lead sheet — lead resists sulphuric acid, which is why lead smelting matters here. Sulphur dioxide from the burner, nitrogen oxides, air and steam feed in; dilute acid collects on the floor.
Chamber acid comes off at roughly 60–70%. The process is slow and continuous, and it is entirely achievable at tier 3. Keep the nitrogen oxides in the system rather than venting them — later plants recovered them in towers. Lead chambers leak where the lead is joined; inspect seams and floor regularly.
✓ Check: Acid collected from the chamber floor weighs roughly 1.5–1.6 kg per litre, and the chamber shows no leaks at its seams.
5 · Measure strength by weighing a litre, and concentrate in glass
Weigh exactly one litre at room temperature — the fastest reliable test you have:
- Water: 1.00 kg.
- About 62% acid: about 1.52 kg.
- About 70%: about 1.61 kg.
- About 98% — oil of vitriol: about 1.84 kg.
Concentrate chamber acid by boiling off water in glass or glazed stoneware, under good ventilation. Near full strength it gives off dense white fumes; stop there. Dilute acid eats iron and copper — use lead, glass or glazed stoneware.
✓ Check: Each batch has a measured weight per litre written on its label, and concentrated acid is held only in glass or glazed stoneware.
6 · Dilute acid into water — never water into acid
Mixing concentrated sulphuric acid with water releases a great deal of heat. Water poured onto acid floats, boils instantly at the surface and throws concentrated acid out of the vessel.
Pour acid slowly into a larger volume of water, in a heat-resistant vessel, stirring, in a thin stream, stopping if it gets hot. Set the vessel in a basin of cold water for large dilutions. Label the result with its strength immediately.
✓ Check: Everyone who handles acid can say, unprompted, which liquid goes into which, and has diluted a batch that way under supervision.
7 · Derive hydrochloric and nitric acid, with their hazards
- Hydrochloric acid: heat salt with sulphuric acid; hydrogen chloride gas comes off and is absorbed in water, up to about 36%. The gas is choking and corrosive; absorb it all.
- Nitric acid: distil saltpetre with sulphuric acid in a glass retort. It attacks almost everything except glass, gold and platinum, and stains skin yellow.
Store nitric acid away from wood, straw, oils and anything organic — it can set them alight.
Brown nitrogen dioxide fumes from nitric acid work cause delayed lung injury: the victim can feel fine and then drown in fluid in the lungs 6–24 hours later. Anyone who breathed brown fumes rests and is watched through the next day.
✓ Check: Each acid is in labelled glass with a glass stopper, nitric acid stored apart from anything organic.
8 · Use it where the return is largest: superphosphate
Phosphate is the nutrient with no substitute. Treating ground bone ash or rock phosphate with sulphuric acid converts insoluble phosphate into a form plants take up quickly — superphosphate, the first industrial fertiliser and a large jump in crop yield on phosphate-poor soil.
Mix in small batches in a lined pit under ventilation, let it cure for weeks, and dry it. Prove it on a test plot: treated and untreated strips side by side, same crop, yields weighed. Then scale. Other uses: pickling metal before plating, battery electrolyte, dye chemistry.
✓ Check: A side-by-side test plot shows a weighed yield difference between the superphosphate strip and the untreated strip.