Protyle (from Greek prōt- proto- + hylē substance) is a hypothetical base substance from which all chemical elements were believed, in the 19th century, to have been formed.
The term "protyle" was coined by the English chemist William Prout in early 19th-century in an attempt to explain the existence of the various chemical elements. He hypothesized that the hydrogen atom was the only truly fundamental object, which he called Protyle, and that the atoms of other elements were actually groupings of various numbers of hydrogen atoms.
In 1886, scientist and Theosophist Sir William Crookes revived the term to refer to original primal matter in an unorganized state, before the evolution of chemical elements. He proposed that this matter would not be hydrogen, but perhaps a half or a fourth part of hydrogen. He considered that this state of primordial matter would be intangible, unable to be perceived by the senses.
- Marco Fontani, et al., The Lost Elements: The Periodic Table's Shadow Side (New York:Oxford University Press, 2015), 406.