According to the Englishman,how were the alchemists he read about changed by the years they spent”in their laboratories, observing the fire that purified the real”

From the text:

"The alchemists spent years in their laboratories, observing the fire that purified metals. They spent so much time close to the fire that gradually they gave up the vanities of the world. They discovered that the purification of the metals had led to a purification of themselves"

What is the meaning to this quote