Topic 6 Airs and The Chemical Revolution

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Topic 6 Airs and The Chemical
Revolution Today We Live Under a Sea of
Air Dr. Joel Benington Dept. of Biology
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Aristotles Four Earthly Elements
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Alchemy the Nature of Matter

• Based on ancient ideas of matter
• Ancient ? medieval
• Experimental
• Developed chemical techniques
• Solitary secret
• Complex, diverse, confused conclusions

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Why Study Air?

• An element (if you believe Aristotle)
• Homogeneousno structure
• But difficult to contain, work with
• Does it have weight?
• Does it fill space? Can there be a vacuum?
• What causes air pressure?
• Is air an element or are there many airs?

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Aristotle air finds its natural place above
earth and water, but below fire
The atmosphere
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Aristotle air finds its natural place above
earth and water, but below fire
The atmosphere
So is it heavy or light?
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Evidence for Weight of Air

• Aristotle a filled bladder weighs more
• Implication the air must have been under
  pressure
• Benington weighed balloons empty and full

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The Bonas Balloon Experiment
Used cotton fibers to absorb moisture in breath.
Filled three balloons to roughly the same
pressure.
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The Bonas Balloon Experiment
Used cotton fibers to absorb moisture in breath.
Filled three balloons to roughly the same
pressure.
437.5 grains per ounce (weight of one barleycorn)
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Evidence for Weight of Air

• Aristotle a filled bladder weighs more
• Implication the air must have been under
  pressure
• Benington weighed balloons empty and full
• Galileo compressed air in glass bottles
• Concluded air is 460 times less dense than water
• (Actually, its about 800 times less dense)

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The Horror Vacui For Aristotle (and Descartes
and others until)

• Space defined by matter occupying it
• Empty space is a logical impossibility
• Matter is everywhere, no void or vacuum
• Nature abhors a vacuum
• The horror vacui
• Will do what is necessary to prevent it
• Contrast Democritus atoms moving in the
  void)

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The Power of the Horror Vacui
1. Draw water up a tube (soda straw water pump
syringe)
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A water pump uses vacuum to pull water up
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The Power of the Horror Vacui
1. Draw water up a tube (soda straw water pump
syringe) 2. Water does not drain from a vessel
unless air can enter to replace it
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The Power of the Horror Vacui
1. Draw water up a tube (soda straw water pump
syringe) 2. Water does not drain from a vessel
unless air can enter to replace it 3. Water
siphon through a tube
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Siphon
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Apparent Limitations to the Power of the Horror
Vacui

• Water pumps cannot lift water more than 34 feet
• Discovered pumping water out of mines
• Water siphon cannot carry water over a hill more
  than 34 feet high
• Water forms 34-foot column in closed tube

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Really big thumb!
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Gasparo Berti (1600-1643)

• Water filled tube
• Level of water inside tube stayed at 34 ft
• Space left above water in tube
• Vacuum in the space above the water?

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Water height is the same, whatever the length of
the tube
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Water height is the same, whatever the length of
the tube
Wouldnt nature more strongly abhor a larger void?
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Torricelli used mercury instead of water
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Torricelli used mercury instead of water
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Torricelli used mercury instead of water
Same pattern, but only 2 ½ feet high
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Torricelli used mercury instead of water
Same pattern, but only 2 ½ feet high
(1/13.6 height of water column and mercury is
13.6 times as heavy as water)
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Torricellis alternate hypothesis to the horror
vacui Perhaps something pushes the water or
mercury up the tubes, and could push up the same
weight of both liquids?
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Torricellis hypothesis Perhaps the weight of
the air (atmosphere) is doing the pushing. We
live under a sea of air Pascals prediction If
so, then there should be less push as one moves
up through the atmosphere, because there would be
less air above the observer.
Blaise Pascal
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In 1648, Pascal sent his brother-in-law Florence
Périer up 3000-foot Mt. Puy-de-Dome with bowls,
tubes and mercury
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The mercury rose to 2 ½ feet minus 3
inches! These results proved that Torricellis
hypothesis was true.
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The mercury rose to 2 ½ feet minus 3
inches! These results proved that Torricellis
hypothesis was true.
NOT!
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The mercury rose to 2 ½ feet minus 3
inches! These results proved that Torricellis
hypothesis was true.
NOT!
These results supported Torricellis hypothesis.
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Today we use the barometer to measure changes
in atmospheric pressure to help predict weather
changes.
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Weather station atop Mt. Puy-de-Dome
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Another test of weight of air hypothesis
Predict that if a barometer is placed in a
chamber and the air pumped out, then the mercury
column will not be as high.
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Boyles/Hookes improved pump of 1660
von Guerickes original air pump
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As air pumped outmercury in barometer dropped
lower and lower down to a small fraction of an
inch. Supports hypothesis that water and mercury
columns were pushed up to their heights by the
weight of air, rather than climbing up in
attempts to eliminate the vacuum.
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Boyles experiments on the spring of air Air
resists compression like a spring does.
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Boyles experiments on the spring of air Air
resists compression like a spring
does. Explanation?
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Boyles experiments on the spring of air Air
resists compression like a spring
does. Explanation? Boyle Air consists of tiny
particles that are like springs, pressing against
each other, and resisting compression.
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Boyles experiments on the spring of air Air
resists compression like a spring
does. Explanation? Boyle Particles of air are
like springs, pressing against each other, and
resisting compression Newton Air particles
repel each other without contact, with a force
that decreases with distance.
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Boyles experiments on the spring of air Air
resists compression like a spring
does. Explanation? Boyle Particles of air are
like springs, pressing against each other, and
resisting compression Newton Air particles
repel each other without contact, with a force
that decreases with distance. Both of these
hypotheses ultimately proved incorrect. (Air
pressure results from the force of air molecules
colliding with surfaces and bouncing off them
exerting force on the surfaces that are equal and
opposite to the forces the surfaces are exerting
on them.)
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But is Air an Element?

• What would persuade you that there are chemically
  distinct airs?
• What properties could be used to identify airs?
• Color? Taste?
• Density?
• What materials it comes from?
• How it reacts with other materials?

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Gases in the Atmosphere

• Gases are one form of matter
• Molecules more separated than in liquids and
  solids
• Composition of atmosphere
• 78 nitrogen gas (N2)
• 21 oxygen gas (O2)
• Argon (0.9), carbon dioxide (0.035), etc.

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Other Common Gases

• Hydrogen gas (H2)
• Nitric oxide (NO)
• Water vapor (H2O)
• Helium (He)
• Methane (CH4)

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Why Were Gases Difficult to Study?

• Hard to keep contained
• Escape and mix with the atmosphere
• Must be kept under pressure
• In bladders? Glass jars?
• They all look alike!
• Colorless, (mostly) odorless

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Early Reports of Distinct Gases

• Non-experimental observations
• Unhealthy air
• Marsh gases, mine damps
• How were these interpreted?
• Van Helmont (early 1600s)
• Produced gases by combustion of various materials
• Produced what we now call carbon dioxide, carbon
  monoxide, sulfur dioxide, chlorine gas
• Called them wild spirits or gas
• From Greek word for chaos

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Robert Boyles Factitious Air

• Used air pump to create vacuum

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Robert Boyles Factitious Air

• Used air pump to create vacuum
• Produced airs by fermentation of organic material
• Cherries, rotting beef, wheat paste, etc.

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Robert Boyles Factitious Air

• Used air pump to create vacuum
• Produced airs by fermentation of organic material
• Cherries, rotting beef, wheat paste, etc.
• Called it artificial air or factitious air

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Robert Boyles Factitious Air

• Used air pump to create vacuum
• Produced airs by fermentation of organic material
• Cherries, rotting beef, wheat paste, etc.
• Called it artificial air or factitious air
• Transferred using evacuated containers

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Is Factitious Air Distinct From Common Air?

• Boyle identified distinct chemical properties of
  factitious air
• Stopped fermentation (again, in air pump)
• Killed animals
• Put out candles
• Problem studies required use of air pump
• Expensive piece of equipment!