HISTORY: ON THE HUMAN SIDE
An interesting historical note: Professor Joseph Black, a noted and very popular lecturer in Edinburgh in the 1770s, appears to be one of the first to have used this test for what he called “fixed air.” In one of his lectures, he demonstrated that respiration produces the same “fixed air” that burning charcoal does: “Into this Glass syphon, I shall pour a quantity of Limewater… I now apply my mouth to the pipe, and suck in the common air through it; The fluid bubbles a little, but it is not altered in its transparency… But I now blow through it, and it becomes instantly muddy, the fixed air from the Lungs being attracted by the Lime, it loses its solubility and is precipitated.”
Leonardo da Vinci (1452-1519) said, “Where flame cannot live, no animal that draws breath can live.” A flame will be extinguished in CO 2 .
Robert Boyle (1635-1691) conducted experiments to show that air has weight, and proposed that air contains a “vital quintessence” essential to animal life. This is oxygen!
Johann Becher (1635-1682) and Georg Ernst Stahl (1660-1734) proposed the “phlogiston theory” to account for burning. Things that burned readily contained more “phlogiston.”
John Clayton (1657-1725) discovered “coal gas” by heating and distilling coal and wood.
Carl Wilhelm Scheele (1742-1786) and Joseph Priestley (1733-1804) independently prepared and described oxygen gas. Priestley discovered nitrous oxide (N 2 O, dinitrogen oxide) in 1772.
Antoine Lavoisier (1743-1794) showed that a component of air was consumed when a substance burned in air. After observing the same effect with a mouse confined in air, he proposed that the reaction with air occurred in the lung of the animal as well. These ideas about burning brought about the downfall of the phlogiston theory.
Daniel Rutherford (1749-1819) discovered nitrogen in 1772. He named the substance “noxious air” because it did not support life. The French word for nitrogen is “azote,” meaning “without life.”
Jan Ingenhousz (1730-1799) showed that plants, with the aid of sunlight, restored air to its “normal state,” that is, provided oxygen, and proposed that plants receive their carbon dioxide from the air.
Nicolas Theodore de Saussure (1767-1845) explained the carbon cycle. He performed quantitative experiments in photosynthesis to show that plants extracted carbon dioxide from the atmosphere, that all the carbon in plants came from this gas, and that water was essential for photosynthesis.