After Borri had been about eleven years in confinement, a small volume was published at Cologne, entitled _The Key of the Cabinet of the Chevalier Joseph Francis Borri, in which are contained many curious Letters upon Chemistry and other Sciences, written by him, together with a Memoir of his Life_. This book contained a complete exposition of the Rosicrucian philosophy, and afforded materials to the Abbé de Villars for his interesting _Count de Gabalis_, which excited so much attention at the close of the seventeenth century.
Borri lingered in the prison of St. Angelo till 1695, when he died, in his eightieth year. Besides _The Key of the Cabinet_, written originally in Copenhagen, in 1666, for the edification of King Frederick III., he published a work upon alchymy and the secret sciences, under the title of _The Mission of Romulus to the Romans_.
INFERIOR ALCHYMISTS OF THE SEVENTEENTH CENTURY.
Besides the pretenders to the philosopher's stone whose lives have been already narrated, this and the preceding century produced a great number of writers, who inundated literature with their books upon the subject. In fact, most of the learned men of that age had some faith in it. Van Helmont, Borrichius, Kircher, Boerhaave, and a score of others, though not professed alchymists, were fond of the science, and countenanced its professors. Helvetius, the grandfather of the celebrated philosopher of the same name, asserts that he saw an inferior metal turned into gold by a stranger, at the Hague, in 1666. He says, that, sitting one day in his study, a man, who was dressed as a respectable burgher of North Holland, and very modest and simple in his appearance, called upon him, with the intention of dispelling his doubts relative to the philosopher's stone. He asked Helvetius if he thought he should know that rare gem if he saw it. To which Helvetius replied, that he certainly should not. The burgher immediately drew from his pocket a small ivory box, containing three pieces of metal, of the colour of brimstone, and extremely heavy; and assured Helvetius, that of them he could make as much as twenty tons of gold. Helvetius informs us, that he examined them very attentively; and seeing that they were very brittle, he took the opportunity to scrape off a small portion with his thumb-nail. He then returned them to the stranger, with an entreaty that he would perform the process of transmutation before him. The stranger replied, that he was not allowed to do so, and went away. After his departure, Helvetius procured a crucible and a portion of lead, into which, when in a state of fusion, he threw the stolen grain from the philosopher's stone. He was disappointed to find that the grain evaporated altogether, leaving the lead in its original state.