“Remove the solid,” said the alchemist, indicating the beaker before continuing his work on the next step.
His assistant hesitated, peering into the beaker and making a face. “Why am I the one who has to stick my hand into the dangerous chemicals?”
“Because your skin is far less susceptible to reaction than mine,” the alchemist replied.  His attention never wavered from his task as he spoke.
“Hm…true…” With no further hesitation, the assistant’s hand dipped into the acidic solution, grabbed the stone-like substance resting at the bottom of the beaker, and pulled it out.  Though the hand had been burned to a deepening red, the assistant seemed to register no pain.  Once the stone had been thoroughly cleaned with distilled water, the assistant presented it to the alchemist.
“Very good,” said the alchemist.  Taking the stone, he set it on a metal plate on the apparatus he had been setting up. “Will your hand be alright?”
“Yes.  It’s already starting to heal, Master,” said the assistant. “Do you think we got it right this time?”
“There is always a chance of success, but the only way to discover if you have indeed succeeded is to test it.” The old alchemist attached an electrode to the stone and another to the plate it rested on. “Flip the switch.”
Obeying, the assistant activated the current that ran between the two substances.  They both watched intently as a few arcs of electricity leapt from stone to metal, then the stone began to glow with a dull red light.  
The assistant’s eyes widened. “Is that—”
“Hush,” snapped the alchemist, as though words could ruin it.
The red light coming from the stone suddenly surged brighter, and when it dimmed the stone had fallen straight through the metal plate to rest on the wooden table beneath it.  The assistant looked hopefully at the alchemist, not speaking for fear of being told to be quiet again.  But the alchemist only shook his head.
“It melted,” he said. “It wasn’t absorbed.”
“Oh…” murmured the assistant, disappointed. “But then that means the stone generated its own heat, its own energy, right?  We didn’t use that much voltage.”
“Yes, but the energy barrier was broken decades ago.  You generate your own energy, after all, and that simply required the proper equation.  This is no breakthrough.”
His assistant nodded and looked at the now-lightless stone. “Should I destroy it then, Master?”
“No.  Swallow it for now,” said the alchemist as he disassembled the apparatus. “We’ll use it as a heat source for tomorrow’s experiment.”
“Yes, Master.” The assistant promptly picked up the stone and swallowed it whole, as if this was nothing out of the ordinary.
With one last moment of silent thought, the white-haired old alchemist left the chamber, closing the door behind him and locking it from the outside.
His assistant remained inside the locked room, tidying up the day’s messes before falling asleep sitting up in the corner behind the bookshelf.