The drops of liquid hit the copper—and suddenly, a loud hiss filled the room. The liquid bubbled up against the copper, and a sharp, intense stench ripped through the air. The fumes coming off the copper were so strong Nick could almost feel them pressing him backward. He started to cough.

“Probably should have told you to hold your breath, too,” Hailey said, between gasps. “Sulfuric acid is an oxidizing agent. When it meets copper, a redox reaction occurs. The acid gets reduced to sulfuric dioxide, a nasty, toxic gas.”

Nick staggered back a foot, still coughing.

“Libra. Sublimation.”

“You’re a fast learner,” Hailey said.

She poured a few more drops onto the page. More hissing, more noxious fumes rising up—but this time Nick stayed a healthy distance away. Even so, he could see Hailey open her eyes wide behind her goggles.

He looked down at the copper page again, and where the acidic liquid had touched the metal, he could now clearly see—the page was no longer blank. It was covered in letters, etched right into the copper.

“How—” he started, but Hailey was already ahead of him.

“It’s pretty simple, actually. You write the letters right onto the copper using something impervious to sulfur. Any oil would work. In Revere’s time, that would most likely be whale oil, which also happens to be very stable. Once the oil dries, it would be invisible against the copper.”

As she was talking, Nick was looking at the page. The noxious fumes had dissipated enough for him to clearly see what was written across the copper. At least a dozen lines of text, running from the top of the page to the bottom. Amazing, how just a moment ago the book had been blank. And now it was filled with—

“Gibberish,” Nick said. “It just looks like random letters. No words, no punctuation.”

Hailey studied the page for a moment. Then she signaled Nick to back up again, and went to work on the next page with the flask and the battery acid. Carefully, she continued through the book. By the time she’d reached the end, the air in the room was thick with vapor. Nick’s lungs felt tight from coughing, and his eyes watered at the edges.

“Lucky for us, the filtration systems in these old labs are made for this sort of thing,” Hailey said, as she tightened the cap back on the flask.

When Nick had recovered sufficiently from the sulfuric dioxide, he joined her back over the book, as she leafed through the rest of the pages. Like the first, they were all filled with row after row of what seemed like random letters. There were no spaces to indicate words, no periods or commas or numbers.