Shakespeare and Oxygen

So Celeste and I were having an argument today, as you do, about whether oxygen had been discovered in Shakespeare's time. I argued that it had, because everyone knows the line in Romeo and Juliet when Juliet says "and with my last breath of 21% oxygen and 78% nitrogen, I die to live, my love".

But I was wrong as usual. Oxygen was discovered in the 1770s and Shakespeare was around in the 1600s. Wikipedia sucks.