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Primary sourceDocument26 November 1784

Thoughts on the Constituent Parts of Water and of Dephlogisticated Air

James Watt · 26 November 1784

Watt's 1784 scientific paper on the composition of water, published in the Philosophical Transactions.

Watt wrote this paper himself, showing his work as a chemist alongside his engineering career.

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Printed journal page numbered 329 from the Philosophical Transactions, showing the title 'Thoughts on the Constituent Parts of Water and of Dephlogisticated Air' by James Watt, a letter to Mr. De Luc, dated Birmingham, November 26, 1784, with body text in running paragraphs and a page footer reading Vol. LXXIV.
James Watt, 'Thoughts on the Constituent Parts of Water and of Dephlogisticated Air', Philosophical Transactions, 1784. Royal Society.

About this source

What it is

This is a printed scientific paper written by James Watt in 1784, published in the Philosophical Transactions of the Royal Society. It takes the form of a letter to Mr. De Luc, written from Birmingham, discussing the chemistry of water and 'dephlogisticated air' (what we now call oxygen). It is held by the Royal Society.

Why it matters

This paper shows that Watt was not only an engineer but also an active chemist, engaging with the leading scientific debates of his day. It led to the long-running 'water controversy', a dispute over who first discovered the composition of water, involving scientists such as Henry Cavendish.

Look closer

  • What does the old-fashioned spelling and printing style tell you about when this was written?
  • Why might Watt have been interested in chemistry as well as engines?
  • What does the existence of a priority dispute suggest about how science worked in the 1780s?

This document is part of the curated material that grounds the AI version of James Watt on Humy.ai — when students ask about related events, the AI can quote it and cite it.

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