The Blackthorn Key

sal ammoniac





litharge





realgar





cinnabar





tartar





marchasite





CORROSIVES



aqua fortis





vinegar





aqua regia





distilled vinegar





oil of vitriol





WEIGHTS & MINERALS



one pound





one ounce





one dram





one scruple





one pinch





one pint





equal amounts





INSTRUCTIONS/PROCESSES



calcination





congestion





fixation





solution





digestion





precipitation





purify





digest





sublimation





separation





ceration





fermentation





multiplication





caput mortuum





oil





filter





sugar





spirit





essence





still





take





alcohol





retort





night





day





honey





wax





powder





distill





mix





compose





receiver





boil





“We already know this is mercury,” I said, pointing to the hole on the left. “The one at the top is . . .”



“. . . air?” I said, puzzled.

Tom reached up and poked his finger in the hole. “Isn’t there air in here already?”

“Maybe that’s the trick.” I turned to the workbenches with the ingredients. “Nothing’s supposed to go in there. But if you don’t have the key, you’d put different things in to try to crack it. So the lock won’t work.” Pretty clever, I thought.

“All right,” Tom said. “Then what’s the last one?”

There were three symbols to match.



A triangle, pointed down. Water.

A curious ladder with a strange zigzag drawn at the bottom. Mix.

A circle, a horizontal line cutting through its center. Salt.

Water, mix, salt.

“Does that mean . . . salt water?” Tom said.

“That’s what I’d guess,” I said. Air on top, mercury on the left, salt water on the right.

We got ourselves ready. I poured water up to the notch in one beaker. I dumped a heaping scoop of salt into it with the spoon on the other table. I stirred it, leaving a cloudy white liquid. A second beaker, filled with mercury, went to Tom.

We stood in front of the dragons. I gave Tom a nod.

Slowly, he poured the mercury in. We heard the faint thunk from behind the plate.

I tipped the salt water. It splashed down inside.

Nothing.

“Did we—”

Clack.

The wall unsealed. A seam appeared, ringed around the inside of the ouroboros. The torch flickered as air rushed through it, whispering in our ears like breath.

The center of the mural swung open. The Archangel Michael beckoned.

I stepped inside.

A new, wide corridor was behind the seal. Here there were no nooks carved in the walls, no more ancient bones, just solid stone. The passage went another twenty feet. It ended in a wooden door.

“Look,” Tom said.

He was staring at the back of the mural. It was glass, so we could see the mechanism behind it, like the design inside my puzzle box. On the right, the mercury held down a lever attached to the lock at the side. On the top, where we’d left nothing but air, was another lever. If anything had been poured inside, it would have slammed down a counterweight, forcing the lock to stay closed.

But the most amazing thing lay opposite the mercury. The salt water I’d poured had gone into a ceramic jar. At its top, between two metal prongs, sparks crackled, brighter than those from a tinderbox. They looked like tiny lightning strikes. With each one came snaps, like baby thunder.