Why Water isn’t H2O
(short answer: cuz it’s a mixture!):
A case study in how the history of
science and science itself loosens the
grip of Realist metaphors
Ken Dickey
Boise State University Philosophy
Nyssa High School Chemistry
The Miracle of Semantic Realism
“Suppose I point to a glass of water and say ‘this is
called “water”’…[T]he body of liquid I am pointing to
bears a certain sameness relation (say, x is the same
liquid as y…) to most of the stuff I and other
speakers…have on other occasions called ‘water’.”
-- Hillary Putnam, “Meaning and Reference”
The Miracle of Semantic Realism
“Suppose I now discover the microstructure of water
– that it is H2O.”
“…the extension of the term ‘water’ was just as much
H2O on Earth in 1750 as in 1950…”
-- Hillary Putnam, “Meaning and Reference
The Miracle of Semantic Realism
In sum, I can point to one thing or one
sample and utter a word. By the miracle
of semantic realism, that word picks out all
other parts of the world that have the
same ?!? as my sample. Of course, this
only works for natural kinds terms like
‘water’.
Characteristics of natural kinds
terms
• “Carve nature at its joints”
• Reveal fundamental patterns of the world
• Pick out the final categories that scientists
ultimately strive for
• Identify things by their “real essence”
(usually microstructural features), not their
“nominal essence”
• Once dubbed, their extension does NOT
depend on human decision-making
Characteristics of natural kinds
terms
• Once dubbed, their extension does NOT
depend on human decision-making
Putative Examples
of Natural vs. non-natural kinds terms
Natural vs. Non-natural
• Temperature (average • Warmth (a judgement
kinetic energy of tiny
that varies from
particles)
individual to
individual)
• ‘x has a temperature
of __ oC’
• ‘x is warm’
Natural vs. Non-natural
• Plant (multi-cellular
organism with cells
containing
chloroplasts and cell
walls)
• ‘x is a plant’
• Mountain (vague rise
in topography)
• ‘x is a mountain’
• Mountain vs. hill
Natural vs. Non-natural
• Globular Cluster
• Constellation
(group of stars formed
(recognizable pattern
from the same nebula
of stars in the sky)
and bound locally by
• Pattern varies with
gravity to form a
location in the galaxy
spherical shape)
• Pattern identification
reflects human
interests
Natural vs. Non-natural
• Ant Colony (grouping
of ants with interdependent roles and
directed by a single
queen ant)
• Penal Colony (a
human institution
created to fulfill
human needs/goals)
It is the appeal to microstructure, I believe, which legitimates (in the
minds of some) what I am terming the “miracle of semantic realism”.
Most people will agree that the extension (or “meaning”) of ordinary
English predicates depends on human decision-making. For example,
there is an active debate now over whether the term ‘marriage’ applies only
to male-female unions, or could also apply to same-sex unions. Again,
there was a recent debate within the scientific community over whether the
term ‘planet’ should apply to bodies as small as Pluto.
But it is believed that some English predicates escape this reliance on
on-going human decision-making (that’s the “miracle”). These are the socalled ‘natural kinds’ terms. What allows these terms to stand on their
own, it is believed, is that, once dubbed, their extension is determined by a
pure microstructure, one which could very well escape the notice of
language users. Once this microstructure takes over the meaning of a
word, connecting it to the fundamental patterns of nature, no amount of
human decision-making can circumvent that (or so it is believed).
Natural vs. Non-natural
• Bird (warm-blooded,
feathered creature
with wxyz DNA
characteristics)
• ‘x is a bird’
• Plane (a human
invention)
• ‘x is a plane’
Natural vs. Non-natural
• Oxygen (element with
atomic number 8)
• Phlogiston (substance
with sometimesnegative weight,
posited by scientists
to explain
experimental results
but later rejected)
Natural vs. Non-natural
• Water (H20)
• ‘x is a bit of water’
• Mud (a mixture
containing water and
“dirt” in unspecified
proportions)
• ‘x is a bit of mud’
A Lesson in the History of Science
Yawn…
How it was discovered that water is H2O
Discovering Water is H2O
Law of Definite Proportions
Water sample A = 18 grams
Joseph Louis Proust
16 g oxygen and 2 g hydrogen
16 g O / 2 g H = 8 O :1 H
Water sample B = 27 grams
24 g oxygen and 3 g hydrogen
24 g O / 3 g H = 8 O :1 H
Sample C = 32 g O / 4 g H = 8 O :1 H
LDP: In a chemical compound, the ratio
of elements is always the same,
regardless of sample.
* Note, this is NOT true of mixtures!
French chemist
Born
September 26, 1754)
Angers, France
Died
July 5, 1826 (aged 71)
Paris,France
Discovering Water is H2O
Law of Multiple Proportions
John Dalton
40 g of Lye (Draino)
23 g Na, 16 g O, 1 g H
16 g O / 1 g H = 16 0 : 1 H
27 g of Water
24 g O / 3 g H = 8 O : 1 H
62 g of Ethylene glycol (antifreeze)
24 g C, 32 g O, 6 g H
32 g O / 6 g H = 5 1/3 O : 1 H
32 g of Methanol (wood alcohol)
Born
September 6,
1766)
Died
July 27, 1844
(aged 77)
12 g C, 16 g O, 4 g H
16 g O / 4 g H = 4 O : 1 H
Discovering Water is H2O
Law of Multiple Proportions
John Dalton
In Lye 1 g H : 16 g O, the lowest ratio, so s’pose
Lye = 1 H : 1 0
In Water 1 g H : 8 g O or 2 g H : 16 g O
Water 2 H : 1 O
In Ethylene glycol 1 g H : 51/3 g O or 3 g H : 16 g O
E. G. = 3 H : 1 O
In Methanol 1 g H : 4 g O or 4 g H : 16 g O
Methanol = 4 H : 1 O
LMP: When the same elements combine into
different compounds, they do so in the ratio of
small whole numbers.
Born
September 6,
1766)
Died
July 27, 1844
(aged 77)
Law of Multiple Proportions
John Dalton
But the ratio of masses says nothing
about the MICROSTRUCTURE of water.
For that we need…………
Discovering Water is H2O
Dalton’s Atomic Theory
(about 1803)
1. All elements are composed of tiny indivisible
particles called atoms.
2. All atoms of the same element are identical. The
atoms of any one element are different from those
of any other element.
3. Atoms of different elements can combine with one
another in simple whole number ratios to form
compounds.
4. Chemical reactions occur when atoms are
separated, joined into molecules, or rearranged.
However, atoms of one element are never created
nor destroyed by a chemical reaction.
Various atoms and molecules as
depicted in John Dalton's A New
System of Chemical Philosophy
(1808).
Dalton’s Atomic Theory
+
2 Hydrogen atoms
1 Oxygen atom
1 molecule of water = H2O
Discovering water is H20
Ta da….
But this is not the end of the story…
What Came Next
What Came Next
•
The Russian chemist Dmitri
Mendeleev organized all of the
known elements into a pattern
that is today considered to be the
first periodic table.
•
Mendeleev’s table allowed him
to predict the existence of
previously unknown elements!
•
Predictive power lent great
credence to the emerging science
of chemistry, founded on Dalton’s
atomic theory.
Mendeleev’s original periodic table
published in 1869 based the order of
elements on their atomic mass.
What Came Next
However…
•
•
•
•
What Came Next
Mendeleev’s table was arranged by atomic
mass.
This created puzzles where a few
elements seemed to be “out of place”.
Trusting the pattern-like character of his
table, Mendeleev insisted the masses of
elements simply had not been accurately
determined.
But the puzzles remained…
What Came Next
• The “fix” could not be had until the
overthrow of Dalton’s atomic theory.
• It started with the discovery of the electron
by J.J. Thomson in 1897.
What Came Next
J.J. Thomson’s famous cathode ray experiment. The degree of deflection
indicated a very high charge-to-mass ratio. These deflected particles must
have been much smaller than even a hydrogen atom.
What Came Next
Dalton’s Atomic Theory
(about 1803)
1. All elements are composed of tiny indivisible
particles called atoms.
Not anymore!
Comment on conceptual vs. empirical revision?
Various atoms and molecules as
depicted in John Dalton's A New
System of Chemical Philosophy
(1808).
What Came Next
Rutherford’s famous experiments involving gold foil soon followed.
What Came Next
He discovered the atomic nucleus and
the proton. His student Moseley
introduced the concept of atomic
number, which justified the correct
placement of elements within the
periodic table.
What Came Next
Still later (1922), the mass spectrometer was used to isolate different
atoms of the same element with different masses. In 1932, neutrons
were discovered and used to explain how these atoms differ.
Isotopes = atoms of the same element with different masses (same
atomic number, but different numbers of neutrons)
What Came Next
Dalton’s Atomic Theory
(about 1803)
2. All atoms of the same element are identical.
Not anymore!
Various atoms and molecules as
depicted in John Dalton's A New
System of Chemical Philosophy
(1808).
What Came Next
The existence of neutrons and isotopes explained WHY Mendeleev’s
arrangement of elements was flawed.
The chemical properties of atoms were determined by the number of
protons (and electrons). But atoms with more protons did not necessarily
have (on average) more neutrons.
So, in a few exceptional cases, elements with a greater atomic number
could still have a lesser atomic mass.
Mendeleev, working with Dalton’s atomic theory, could never have known
this.
More to the point…
Three isotopes of hydrogen
Protium
Deuterium
Tritium
In any actual sample of water, all of these isotopes will be integrated
within water molecules. That means, we could have:
P2O (almost all naturally occurring water)
DPO (about 1 in 3200 natual water molecules)
D2O (about 1 in 41 million water molecules)
PTO (trace)
DTO (trace)
T2O (trace)
And all are “water” molecules!
A Strong Intuition of Mine
At the time of discovering isotopes of hydrogen, scientists COULD HAVE
decided that only P2O is really water, and that DPO (and D2O) are impurities.
Since they did not make that decision, it remains acceptable to say that water is
H2O. Still, the fact that there was such a “decision point” casts doubt on
whether the term ‘water’ uttered in 1750 referred to H2O once and for all,
independently of all subsequent decision-making. That is, it casts doubt on
whether the term ‘water’ IS a natural kind term.
Characteristics of natural kinds
terms
• “Carve nature at its joints”
• Reveal fundamental patterns of the world
• Pick out the final categories that scientists
ultimately strive for
• Identify things by their “real essence”
(usually microstructural features), not their
“nominal essence”
• Once dubbed, their extension does NOT
depend on human decision-making
Philosophical Upshot
• The discovery that water is H2O rests on a
theory of the atom that has since been
supplanted.
• A more modern theory of the atom still
accepts the claim that water is H20, but would
insist there is more going on than just that.
• This casts doubt on whether ‘water’ picks out
a “final category that scientists ultimately
strive for”.
So much for the history of science…
What about the science of water itself?
The Miracle of Semantic Realism
In sum, I can point to one thing or one
sample and utter a word. By the miracle
of semantic realism, that word picks out all
other parts of the world that have the
same ?!? as my sample. Of course, this
only works for natural kinds terms like
‘water’.
A new start to the debate…
Any sample of ordinary water dubbed as ‘water’
in 1750 was surely a MIXTURE of H2O with gobs of
other stuff!
A new start to the debate…
So it will be difficult to isolate what the essential
features of water are such that all subsequent
samples of water have the same ?!? as the
originally dubbed sample of water.
A new start to the debate…
Another way to see this point is through pH or even
perhaps taste testing.
A new start to the debate…
Ordinary samples of water simply do not have
the same pH (or taste!) as so-called “pure” water.
The next step…
But surely we can PURIFY water to remove
everything except the H2O, can’t we?
(Not really, as we shall see)
Even the ancients could collect RAIN water,
which is free of original contaminants.
(But not of “new” contaminants, as we shall see)
The Water Cycle
The next step…
Meanwhile, high up in the clouds, chemical reactions are occurring…
Nitrous Oxide (from lightning or internal combustion)
NO + ½ O2  NO2
3NO2 + H2O  NO + 2 HNO3 (Nitric acid)
Sulfur Dioxide (from volcanoes or coal burning)
SO2 + ½ O2  SO3
SO3 + H2O  H2SO4 (Sulfuric Acid)
Carbon Dioxide (from decomposition, burning, exhaling)
CO2 + H2O  H2CO3 (Carbonic Acid)
A new start to the debate…
So regular rain water has a pH of about 5, and even
lower (so-called “acid rain”), if it is subjected to very
high levels of industrial pollution.
Another avenue for debate…
O.K. Appealing to rain water for “pure” water was a
bad idea. Still, we can get pure water here on the
ground through the process of distillation.
Distillation Apparatus
Impurities remain behind as only H2O boils and condenses
Another avenue for debate…
You don’t have to go up high into the atmosphere to
run into the problem of atmospheric gases
dissolving in water. The atmosphere will “come to
you”!
(Note: this is why fish can breathe underwater)
Atmospheric and dissolved gases are continually exchanged through a
dynamic equilibrium
Another avenue for debate…
Henry’s Law:
“At a given temperature the solubility of a gas in a
liquid is directly proportional to the (partial) pressure
of the gas above the liquid.”
Upshot: Even distilled water is impure, insofar as
it has dissolved gases in it.
*At 20oC and 1 atm, water is 0.0023% dissolved air (by mass).
Dickey’s Corollary to Henry’s Law:
“If there is any gas whatsoever near the surface of a
liquid, some of that gas is going to get dissolved into
the liquid.”
Yet another try…
All right, then. Let’s REMOVE the atmosphere
entirely!
•Even if there isn’t a naturally-occurring place on
Earth that is atmosphere-free, we can CREATE
such a place in the lab.
•As philosophers can certainly IMAGINE water
existing in the absence of any atmosphere to cause
contamination.
Yet another try…
Interesting idea… Do you know what HAPPENS to
water when you remove all of its atmosphere?
It boils!
Check it out!
Then you don’t have water at all (which is a liquid),
but instead a vapor.
The final rejoinder…
Not if NOT ALL of the water boils! Then you could
have an equilibrium with liquid water, H20 vapor, and
H20 vapor dissolved in the liquid water.
The final rejoinder…
Then perhaps you could still say that water is a
“mixture”, but it would be a mixture consisting
ENTIRELY of H2O!
And this water “mixture” really DOES have a pH of 7
The final rejoinder…
Is THAT supposed to be what people were talking
about in 1750, when they used the term ‘water’ to
describe what they were drinking, bathing in,
watering plants with, etc.?
The final rejoinder…
That’s the way natural kinds terms work!
You use a word, but neither you nor anyone has to
know what the word refers to. That’s something to
be discovered by scientists, no matter how long and
complex the process is.
As it turns out, water – PURE WATER – really is
nothing but H2O!
There is just one little problem…
H2O molecules are constantly in motion,
crashing into one another, jostling, and even
scraping parts off of one another.
Self-ionization of water shockwave animation
Self-ionization of H2O
H2O
+
H2O
OHHydroxide
ion
+
H3O +
Hydronium
ion
One little problem…
At 25oC, Kw for this process is 1.0 x 10-14
(That’s why the pH scale ranges up to 14.)
This means that for “pure” water,
[H3O+] = 1.0 x 10-7 M (hence the “7” for pH);
[OH-] = 1.0 x 10-7 M
Combined, these impurities occur at a concentration
of 2.0 x 10-7 M, and since water itself has a
concentration of 56 M, this means…
One little problem…
[Ions] / [H2O] = 2.0 x 10-7 / 56 = 3.6 x 10-9
This means that for every sample of water,
0.00000036%
of the water is NOT H20, no matter what lengths one
takes to purify it!
One little problem…
So water is not really just H2O, no matter how
pure you try to make it.
One little problem…
Conclusions
1. That water is H2O is a prime exemplar of
essentialism in semantics. ‘Water’ is held to be a
natural kind term that “carves nature at its joints”
because of the supposed truth of this claim.
Conclusions
2. But the discovery that water is H2O is part of an
unfolding historical process, one which has since
moved beyond the claim in question, onto what are
arguably even more fundamental ways to “carve up
reality”.
Conclusions
3. Furthermore, what ordinary people for centuries
have taken to be water is NOT purely H20, but is
instead a mixture that at the very least contains
dissolved gases from the atmosphere.
Conclusions
4. And finally, there is simply no possible way to purify
water so that it is not a mixture (i.e., so that it contains
only H2O). At the very least, it must contain trace
quantities of hydronium and hydroxide ions.
Conclusions
In sum, the term ‘water’ does not carve nature at its
fundamental joints, and the identification of water with
H20 is, strictly speaking, false.
It is, no doubt, and extremely useful idealization of
what’s really going on with water.
But useful idealizations are not what Semantic Realism
promises.
Limitations
Water being only one example, this argument
certainly can not disprove realism in semantics, nor can
it establish that there are no natural kinds terms.
Benefits
But: for those of us who are suspicious about claims
that scientists have arrived at a final answer about
anything, or claims that certain words carve reality at its
joints, pointing out that ‘water’ is NOT the clear
example that many take it to be does provide some
satisfaction.
Benefits
And for those who are watching the debate from the
sidelines, this argument might help them to remain in
an appropriately skeptical state of suspended
judgement.
Benefits
Finally, it is time to recognize that general plausibility
of the view that there are natural kinds terms at all
relies more on some compelling metaphors rather than
a close examination of details. To learn that water is
NOT H2O will, I hope, loosen the grip of those Realist
metaphors.
A P.S. Rejoinder?
• O.K., so water is not just H2O; it is a mixture.
Still, that doesn’t prove ‘water’ is not a natural
kind term.
• Water, we have learned, is really a mixture
consisting mostly of H20 with 1.0 x 10-7 M of
hydronium ions and 1.0 x 10-7 M of hydroxide
ions.
• People who have used the term ‘water’
throughout history, without realizing it, were
referring to that mixture.
A P.S. Rejoinder?
• This response is really an example of getting the point
but not getting the lesson.
• Any argument of the form ‘x is too simple because of y’
can be met with the response that ‘x is now modified to
take into account correction y’.
• But to go on to assert that the modified x is now the final
answer, or even that there is a final answer, is to make a
leap of faith.
• The lesson of the case-study for ‘water’ is that this leap of
faith is not justified.