[The doctrine of air] I was led into in consequence of inhabiting a house adjoining to a public brewery, where I at first amused myself with making experiments on the fixed air [carbon dioxide] which I found ready made in the process of fermentation. When I removed from that house I was under the necessity of making the fixed air for myself; and one experiment leading to another, as I have distinctly and faithfully noted in my various publications on the subject, I by degrees contrived a convenient apparatus for the purpose, but of the cheapest kind.

Letter to Dr. Price (Oct. 19, 1771) as quoted in John Towill Rutt, Life and Correspondence of Joseph Priestley (1831)