Newton's Alchemy and early Geochemistry

Sir Isaac Newton (1642-1727) is today remembered for his contributions to optics, mechanics and gravity, but as a typical polymath of his time he was also interested in alchemy. And through his interest in this early predecessor of chemistry he became also involved in some geological research.

The theologian and naturalist Thomas Burnet submitted an early draft of his "Telluris theoria sacra" to Newton in 1680-1681 and Newton exchanged with Burnet some thoughts on the formation of the rocks, mountains and the earth. Based on his observations of crystallization of molten tin and saltpeter from water, but also curdling of milk when beer is added to it, Newton imagined earth's matter somehow crystallizing from the primordial, undifferentiated chaos.

Newton never published in full his geological ideas - but some surviving notes deal with (early) geochemical concepts. Two notes, dated to 1670, entitled "Of Natures Obvious Laws & Processes in Vegetation" and "Humores mineralis" deal with the "sal nitrum" theory.  The crystallization of saltpeter, or potassium nitrate (KNO3), is easily observable both in nature as in the laboratory and it was considered by many naturalist of Newton's time as ideal model to understand mineral growth and finally the genesis of ore veins in mountains. 

Alchemy regarded saltpeter even as a sort of philosopher's stone, able to transform into other minerals.

Fig.1. "The Alchymist, In Search of the Philosopher’s Stone, Discovers Phosphorus, and prays for the successful Conclusion of his operation, as was the custom of the Ancient Chymical Astrologers", by Joseph Wright of Derby (1771).

This transformation could explain why minerals were abundant on earth, despite the perpetual dissolution by groundwater percolating into the underground, Newton explains in "Humores mineralis":

"with the metals continually drawn downwards, never ascending so long as they remain metals, it would be necessary that in a few years the greatest part would have vanished from the upper earth, unless they are conceded to be generated there de novo."

The term "vegetation" in the title of Newton's other note refers to the idea of a spontaneous force generating new metals in the centre of earth and injecting them into earth's crust - alchemy considered principles influencing the inorganic nature very similar (or even identical) to life processes. It's therefore no wonder that Newton describes fluids and vapours ("spirits") mating in earth's crust to give birth to the progenitors of metals:

"Indeed, these spirits meet with metallic solutions and will mix with them. And when they are in a state of motion and vegetation, they will putrefy [and] destroy the metallic form and convert [it] into spirits similar to themselves. Which can then ascend again and thus a perpetual circulation of metals takes place."

These progenitors derived from saltpeter, especially sulphur and mercury as most important elements in alchemy, will continue to migrate to the surface, where they transform and are deposited as other useful metals. Such metaphysical explanations for the origin of rocks will prevail for a long time in history.

Bibliography:

NEWMAN W.R. (2009): Geochemical concepts in Isaac Newton's early alchemy. In Rosenberg, G.D., ed., The Revolution in Geology from the Renaissance to the Enlightenment. Geological Society of America Memoir 203: 41-49