Chances are, you’re not like me: you cringe when someone says the word “chemistry.” Your memory of it vaguely harkens back to an undergrad class whose knowledge you flushed once you finished the final. That’s okay — my goal for this series is to change that paradigm, make it understandable to all, and provide some entertainment.
How do you perform an experiment on a substance that is formless, has no taste or smell, and is invisible? While it’s tough for a modern scientist to envision, it’s damn near impossible for a 17th century aspiring chemist relying on a 2000 year old theory of matter. Determining the composition of air seems like dead-end research project perfect for forcing onto a poor, unsuspecting grad student. However, these “pneumatic” experiments set the table for a revolution.
First, let’s talk about the apparatus used for these air experiments, or the method of “collecting gas over water.” If you haven’t been scientifically trained, the operation of this apparatus will not be intuitive — I know this from experience. For a few years as a college-level instructor, the gen chem class I taught culminated in a very open-ended question (“how much gas, if any, is dissolved in this commercially sold beverage?”) to which the students had to answer by devising and performing an experiment. The easiest way to answer the question was devise an apparatus that collected gas over water, but we didn’t tell them that — we wanted them to figure it out on their own. Watching them struggle to have that breakthrough moment in both thought and research on how to design an experiment to answer that question really makes you question your value as an instructor of chemistry, especially when the answer was a 300 year old lab apparatus. But that’s debate we can have at another time. Anywho, the apparatus can be seen below.
Moving from left to right, there is a reaction vessel that generates gas, which travels through a pipe to another vessel. Sometimes, that pipe will have a reagent in it to purify the gas before it is collected. The vessel on the right had been completely filled with water such that when gas is bubbled in, it displaces the water within the vessel. In the early 18th century, there were several different variations of these, but they all had the same basic premise of collecting some sort of gas by displacing liquid in a vessel. They were like messaging apps: WhatsApp, Viber, Signal, iMessage, Google Messages, SnapChat, etc. all do the same basic thing (send messages to people), but have subtle differences.
At this period in time, the word “gas” is relatively new — up until this point, all gas was just called air. In trying to study various different “airs,” a previous chemist kept breaking his collection vessels, so he coined the term “gas,” after the Greek word for chaos (Johann von Helmont was his name). As the term hadn’t gained popularity yet, the pneumatic chemists referred to their gases as “airs,” e.g., “dephlogisticated air.”
Speaking of pneumatic chemists, I’m over how formal that sounds, so from now on, they are the Hot Air Boiz.
The Hot Air Boiz all hailed from Britain. Education was still tough to come by, and if you were poor, many times you had to rely on ministry to obtain reading and writing skills. Accordingly, several preachers went on to become practicing scientists. This was the path of OG Hot Air Boi Joseph Priestly, who started off much like PT Barnum as the son of tailor. He obtained his initial education through ministry and soon took up teaching. After he spent time writing and meeting up with other scientists, he gained a sponsorship.
No — he didn’t have to mention Mountain Dew every time he blew up a reaction vessel, this wasn’t that kind of sponsorship. In that era, a sponsorship was a rich nobleman paying an aspiring scientist (who wouldn’t normally have the means to afford a lab) to perform scientific investigation. Sometimes, the sponsorship was purely philanthropic; other times, it could be in the interest of economic or profit-margin-increasing reason. Consequently, this enabled the OG Hot Air Boi to make impactful discoveries in the field of “airs.”
Of note, while he was apparently enthusiastic and resourceful in his experimental skill, Priestly had the direction of a 15 month old running at full clip: he was all over the place (if you’ve never seen a pre-toddler run, you gotta check it out). Nonetheless, in August of 1774, he dropped his soon-to-be smash hit: he discovered oxygen. He didn’t call it that, and he didn’t recognize that it was elemental, but he did isolate it by a series of experiments on heating “red calx of mercury” (mercury oxide) in air… again with the fire!
“Why red calx of mercury?” you ask? It was about this time that Priestly replaced the water in his gas collection experiment with mercury (mercury was believed to be non-reactive with gases). On heating, the oxygen in mercury calx is liberated first, but then mercury is also vaporized. In the end, the oxygen and vaporized mercury is bubbled into the mercury gas collection vessel. The mercury condenses out with the bulk mercury, and he was left with pure oxygen.
He called this gas dephlogisticated air due to the working theory about phlogiston, which went like this: substances, when burned, transferred their phlogiston to air. A certain quantity of air can only accept a certain quantity of phlogiston, so, for example, when a candle goes out in a closed vessel, it’s because the air is fully phlogisticated. Dephlogisticated air is the exact opposite of that — it’s fully void of phlogiston and ready to accept whatever you have to offer. Further, it’s a component of “common air” (for once, this term is self-explanatory: common air is in fact just regular air) that combines with phlogiston and is responsible combustion.
This analysis taken by itself is sound. Oxygen is responsible for combustion, but it isn’t the result of a transfer of an element. Regardless, many saw this as further proof for the existence of phlogiston, and busting this theory would become central to the progression of chemistry. It would become the center of many important investigations in the coming years, and ironically, dephlogisticated air would be used to disprove the existence of phlogiston at which point, it would be renamed to oxygen by the Hugh Hefner of chemistry.
That story is yet to come, BOLO — first, we need to talk about the other Hot Air Boiz (part II is on its way).
Brock, William H. The Chemical Tree: A History of Chemistry. New York: Norton and Co, 2000.
Ihde, Aaron J. The Development of Modern Chemistry. New York: Dover Publications, 1984.
American Chemical Society International Historic Chemical Landmarks. Antoine-Laurent Lavoisier: The Chemical Revolution. http://www.acs.org/content/acs/en/education/whatischemistry/landmarks/lavoisier.html (accessed March 20, 2021).