Actually, the book suggests that Priestley's most important discovery wasn't oxygen but rather carbon dioxide.
I am always looking for the unlikely connections, so I was taken in early in this book when Johnson wonders how much of the Enlightenment we might owe to coffee.
We start at the London Coffee House in 1765. Priestley is talking with his fellow scientific thinkers. This was an age when there was a move from pubs and liquor to a coffeehouse culture. Many drunken conversations became sober ones stimulated by caffeine.
Johnson likes to mix historical periods and disciplines. In his book, Everything Bad is Good for You, he mixed studies of the brain and pop culture. He argued that things like video games don't make you stupid; they make you smarter.
In another of his books, The Ghost Map: The Story of London's Most Terrifying Epidemic--and How It Changed Science, Cities, and the Modern World, he examines the great cholera epidemic of 19th-century London.
I heard Johnson interviewed and he said he was struck in reading the correspondence between Thomas Jefferson and John Adams that there were five references to Benjamin Franklin and three to George Washington, but there were 52 to Joseph Priestley.
In the "Intermezzo" section to the book, we go back to oxygen's "early days." Around 300 million B.C. - the advent of life on earth during the brief Carboniferous era - is when plant life was in its heyday with giant trees and leaves, and all of that led to a rise in the oxygen content of the atmosphere. It changed the air. And then when all that vegetative stored energy decayed, it coal. That coal polluted the air, but also fueled the industrial age Priestly lived in.
When Priestley comes to America after our Revolution, he connects science and American politics. Johnson writes that "The American experiment was, literally, an experiment, like one of Priestley's elaborate concoctions in the Fair Hill lab. The political order was to be celebrated not because it had the force of law, or divine right, or a standing army behind it. Its strength came from its internal balance, or homeostasis, its ability to rein in and subdue efforts to destabilize it."
Thomas Jefferson admired his writings and his stand against the worship of saints and the divinity of Jesus.
Jefferson gave Priestley credit for developing a Deistic faith that did not include 'supernatural" beliefs. It had a strong impact on many of the founding fathers. I don't think it is widely known that as President, Jefferson occasionally attended church services, but was not a member of any Christian church. He refused to proclaim any national days of prayer or thanksgiving.
In letters he wrote, Jefferson said he was a "Materialist" and a "Unitarian" and rejected the Christian doctrine of the "Trinity" and that of an eternal Hell. Jefferson specifically named Joseph Priestly as one who was "the basis of my own faith." In the "Jefferson Bible", he removed quite literally with a blade the portions he could not reconcile with his beliefs. But Jefferson, as with other Deists, believed in a God.
According to the Encyclopedia Britannica
"By the end of the 18th century deism had become a dominant religious attitude among upper-class Americans, and the first three presidents of the United States held this conviction, as is amply evidenced in their correspondence."Benjamin Franklin, another Deist, was a friend with his fellow inventor, Priestley.
Deism (from the Latin word "deus" meaning "god") is a theological/philosophical position that combines the rejection of revelation and authority as a source of religious knowledge. It reaches the conclusion that reason and observation of the natural world are sufficient to determine the existence of a single creator of the universe. It does not mean no belief in a God.
In The Age of Reason by another famous Deist, Thomas Paine, he writes that “The true deist has but one Deity; and his religion consists in contemplating the power, wisdom, and benignity of the Deity in his works, and in endeavoring to imitate him in every thing moral, scientifical, and mechanical.” (You can read/download The Age of Reason in PDF here.)
Johnson even brings Priestly into our own Information Age, pointing out Priestley's openness in the way that we talk now about "Open Everything" from computer code to textbooks and educational resources. He believed in the the "free flow of information" and shared his work, data and observations to the point that it probably lost him some credit for discoveries.