While not a great deal is known about the life of John Fredrick Schweitzer, called Helvetius, his place in the history of alchemy is secure because, according to tradition, he witnessed a genuine transmutation of base metal into gold and later replicated the process in the presence of doubtful observers.
On December 27, 1666, when he was working in his study at the Hague, a stranger appeared and informed him that he would remove all Helvetius's doubts about the existence of the philosopher's stone that could serve as the catalyst to change base metals
into gold because he possessed such magic. The stranger immediately drew from his pocket a small ivory box, containing three pieces of metal of the color of brimstone and, for their size, extremely heavy. With those three bits of metal, the man told Helvetius, he could make as much as 20 tons of gold.
Helvetius examined the pieces of metal, taking the opportunity of a moment's distraction to scrape off a small portion with his thumbnail. Returning the metal to his mysterious visitor, he asked that he perform the process of transmutation before him.
The stranger answered firmly that he was not allowed to do so. It was enough that he had verified the existence of the metal to Helvetius. It was his purpose only to offer encouragement to alchemical experiments.
After the man's departure, Helvetius procured a crucible and a portion of lead into which, when the metal was in a molten state, he threw the stolen grain he had secretly scraped from the stranger's philosopher's stone. The alchemist was disappointed when the grain evaporated and left the lead in its original state. Thinking that he had been made the fool by some mad burgher's whimsey, Helvetius returned to his own experiments, forgetting about the dream of a magical philosopher's stone.
Some weeks later, when he had almost forgotten the incident, Helvetius received another visit from the stranger. He impatiently told the man to perform a transmutation before his eyes or to leave.
This time the stranger surprised him by agreeing to prove that what he and his brother alchemists most desired truly did exist. He admonished Helvetius that one grain was sufficient for the process to be accomplished, but it was necessary to wrap it in a ball of wax before throwing it on the molten metal, otherwise its extreme volatility would cause it to vaporize. To the alchemist's astonishment and his great delight, the stranger transmuted several ounces of lead into gold. Then he permitted Helvetius to repeat the process by himself, allowing the alchemist to convert six ounces of lead into pure gold.
Helvetius found it impossible to keep a secret of such immense value and importance. Soon the word of his remarkably successful experiments spread throughout Holland, and Helvetius demonstrated the power of the philosopher's stone in the presence of the Duke of Orange and many other prestigious witnesses. The duke's own goldsmith assayed the gold and declared it to be of highest quality. The famous philosopher Baruch Spinoza (1632–1677) visited Helvetius in his laboratory and examined the crucible and gold for himself. He left the alchemist convinced that the transmutation had been authentic.
Soon, after repeated demands for such incredible demonstrations, Helvetius had exhausted the small supply of catalytic pieces that he had received from the mysterious stranger. Search as he might, Helvetius could not find the man in all of North Holland nor learn his name, and the stranger never again visited him.