Lawrence Principe, with William Newman, argued that the division between alchemy and chemistry is a retrospective invention rather than a distinction anyone was drawing in the seventeenth century. The words alchemy and chemistry were used interchangeably at the time, the same people did the same work under both, and the separation was imposed afterwards from two directions at once: by Enlightenment historians of chemistry wanting to disown an embarrassing ancestry, and by nineteenth century occultists claiming alchemy as a purely spiritual discipline that had nothing to do with furnaces. They proposed the older spelling chymistry as a term for the undivided practice.
The consequence for reading the sources is substantial. Robert Boyle, long presented as the figure who separated the two, was deeply engaged in transmutational work; Newton alchemical papers cease to be an eccentricity requiring explanation and become part of a normal research programme. And the corpus stops sorting neatly into serious and superstitious, which is precisely the sorting that had been doing the work in earlier accounts.
The occultist half of the split is worth spelling out, because this atlas inherits it. In the middle of the nineteenth century writers including Mary Anne Atwood and Ethan Allen Hitchcock argued that alchemy had never been about metals at all and that the furnace language was a screen for interior transformation, and Jung later gave that reading an enormous audience by treating alchemical imagery as a projection of psychic processes. The interpretation is a real historical object in its own right. It is not a description of what seventeenth century practitioners were doing.