Furnaces, 1657.

Woodcut. The furnace had symbolic meaning in alchemy. It was not just a piece of apparatus to heat up and purify metals. Alchemists believed that the metal (and thus the human soul) experienced suffering and mortification while being cleansed of its impurities and corruption. Illustration from 'Le Vray et Methodique Cours de la Physique Resolutive Vulgairement dite Chymie' ('The True and Methodical Course in Resolutive Physick, Commonly called Chemistry'), by Annibal Barlet, published in Paris in 1657. Although the book contains a great deal of alchemical jargon, it is for the most part good practical pharmaceutical chemistry. Barlet gave regular chemical courses in Paris, attended by the diarist John Evelyn (1620-1706) amongst others.