The preparation of silver and gold.

“The preparation of silver and gold. Diocletian sought out and burned books about this.
[It is said] that due to the Egyptians’ revolting behavior Diocletian treated them harshly and murderously. After seeking out the books written by the ancient [Egyptians] concerning the alchemy of gold and silver, he burned them so that the Egyptians would no longer have wealth from such a technique, nor would their surfeit of money in the future embolden them against the Romans.”

Suda On Line: Byzantine Lexicography: Emperor Diocletian burned Alchemy books around 292-296. Adler number: chi,280