Hasok Chang: The Boiling Point Myth

The Boiling Point Myth

Hasok Chang [now working in the Department of History and Philosophy of Science at Cambridge] is a philosopher who actually repeats experiments performed centuries ago.

His experimentation [with boiling water] has revealed [the once common scientific knowledge] that explaining the phenomenon of boiling water is challenging and that determining the boiling point of water is problematic.

We all learn at school that pure water always boils at 100°C (212°F), under normal atmospheric pressure.

Like surprisingly many things that “everybody knows”, this is a myth.

We ought to stop perpetuating this myth in schools and universities and in everyday life: not only is it incorrect, but it also conveys misleading ideas about the nature of scientific knowledge.

And unlike some other myths, it does not serve sufficiently useful functions.

There are actually all sorts of variations in the boiling temperature of water.

For example, there are differences of several degrees depending on the material of the container in which the boiling takes place.

And removing dissolved air from water can easily raise its boiling temperature by about 10 degrees centigrade.

The fickleness of the boiling point is something that was once widely known among scientists.

It is quite easy to verify, as I have learned in the simple experiments that I show in this paper.

And it is still known by some of today’s experts.

So actually the strange thing is: why don’t we all hear about it?

Not only that, but why do most of us believe the opposite of what is the case, and maintain it with such confidence?

How has a clear falsehood become scientific common sense?

The Myth of the Boiling Point – Hasok Chang – 2007
Department of Science and Technology Studies – University College London

The ambiguities associated with the boiling point of water are effectively masked [from the casual reader] when Wikipedia [for example] defines the modern “conventions” regarding the “standard” boiling point of water.

There are two conventions regarding the standard boiling point of water:

The normal boiling point is 99.97 °C (211.9 °F) at a pressure of 1 atm (i.e., 101.325 kPa).

The IUPAC recommended standard boiling point of water at a standard pressure of 100 kPa (1 bar) is 99.61 °C (211.3 °F).

For comparison, on top of Mount Everest, at 8,848 m (29,029 ft) elevation, the pressure is about 34 kPa (255 Torr) and the boiling point of water is 71 °C (160 °F).


However, the ambiguities associated with the boiling point of water are illustrated by a thermometer from the 1750s made by George Adams [official scientific instrument-maker to King George III] which is preserved by the Science Museum in London.

Water Boyles

For example, an ambiguity investigated by Jean-André Deluc [a Swiss geologist and meteorologist] regarded the degree to which dissolved air influenced the boiling point of water.

A further puzzle awaited De Luc.

He noticed that the presence of dissolved air in water induced what seemed like premature boiling.

He tried to take the air out by various methods, but in the end decided that he needed to shake a sealed bottle of water for a long time, in addition to all else (remember how shaking a bottle off fizzy drink releases bubbles of gas).

He reported:

This operation lasted four weeks, during which I hardly ever put down my flask, except to sleep, to do business in town, and to do things that required both hands.

I ate, I read, I wrote, I saw my friends, I took my walks, all the while shaking my water.

Four mad weeks of shaking had its rewards.

De Luc’s precious airless water reached 112.2°C before boiling off explosively.

The Myth of the Boiling Point – Hasok Chang – 2007
Department of Science and Technology Studies – University College London

These ambiguities were studied by a special committee appointed by the Royal Society in 1776.

In 1776 the Royal Society of London appointed an illustrious seven-member committee to make definite recommendations about the fixed points of thermometers.

The Royal Society Committee did take it for granted that the two water points should be used, but addressed the widespread doubts that existed about their true fixity, particularly regarding the boiling point.

The Committee’s published report started by noting that the existing thermometers, even those made by the “best artists,” differed amongst themselves in their specifications of the boiling point.

The differences easily amounted to 2-3 degrees Fahrenheit.

Two causes of variation were clearly identified, and successfully dealt with.

First, the boiling temperature was by then widely known to vary with the atmospheric pressure, and the Committee specified a standard pressure of 29.8 English inches (roughly 757mm) of mercury, and also gave a formula for adjusting the boiling point according to pressure, in case it was not convenient to wait for the atmosphere to assume the standard pressure.

The second major cause of variation was that the mercury in the stem of the thermometer was not necessarily at the same temperature as the mercury in the thermometer bulb.

This was also dealt with in a straightforward manner, by means of a setup in which the entire mercury column was submerged in boiling water (or in steam coming off the boiling water).

Thus the Royal Society Committee identified two major problems, and solved both of them satisfactorily.

Royal Society committee on thermometry – Hasok Chang

However, other ambiguities were not so easily resolved and the special committee very ingeniously agreed upon an empirical compromise that fixed the boiling point of water based upon the temperature of steam coming off boiling water [i.e. not the temperature of the boiling water].

The Royal Society committee recorded various types of variations in the boiling temperature of water. Henry Cavendish, who chaired the committee, left us a rather enigmatic statement in one of his unpublished manuscripts:

“The excess of the heat of water above the boiling point is influenced by a great variety of circumstances.”

Royal Society committee on thermometry – Hasok Chang

Thus the use of steam enabled the Royal Society Committee to obviate divisive and crippling disputes about theories of boiling.

It gave a clear operational procedure that served well enough to define an empirically fixed point, though there was no agreed understanding of why steam coming off boiling water under a given pressure should have a fixed temperature.

Is the steam point more fixed than the boiling point? – Hasok Chang

Unsurprisingly, the scientific community continued [and continues] to investigate these ambiguities.

For example, in the 1810s Joseph-Louis Gay-Lussac in Paris reported that water boiled at 101.2°C in a glass vessel, while it boiled at exactly 100°C in a metallic vessel.

This result became fairly well known, but there was no definitive explanation of it available for a long while.

In 1842 François Marcet in Geneva extended Gay-Lussac’s work and reported that water could reach over 105°C in a glass vessel treated with hot sulphuric acid.

This set off a whole line of research in which different researchers competed with each other to attain higher and higher temperatures of pure liquid water under normal atmospheric pressure.

This “superheating” race was won, as far as I can ascertain, by a German named Georg Krebs, who achieved an estimated 200°C in 1869.

The Myth of the Boiling Point – Hasok Chang – 2007
Department of Science and Technology Studies – University College London

In physics, superheating (sometimes referred to as boiling retardation, or boiling delay) is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling.

Superheating is achieved by heating a homogeneous substance in a clean container, free of nucleation sites, while taking care not to disturb the liquid.

There is a common belief that superheating can occur only in pure substances.

This is untrue, as superheating has been observed in coffee and other impure liquids.

Impurities do prevent superheating if they introduce nucleation sites (rough areas where gas is trapped); for example, sand tends to suppress superheating in water.

Dissolved gas can also provide nucleation sites when it comes out of solution and forms bubbles.

However, an impurity such as salt or sugar, dissolved in water to form a homogeneous solution, does not prevent superheating.



Supercooled and Glassy Water – Pablo G. Debenedetti and H. Eugene Stanley – 2003

Currently, 238 years after the Royal Society established its special committee, the scientific community has an agreed theoretical position regarding the boiling point of water.

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.


Vapor pressure or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system.

The equilibrium vapor pressure is an indication of a liquid’s evaporation rate.

It relates to the tendency of particles to escape from the liquid (or a solid).

A substance with a high vapor pressure at normal temperatures is often referred to as volatile.



Accordingly, the Settled Science of water is encapsulated in a Phase Diagram.

A phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions at which thermodynamically distinct phases can occur at equilibrium.

In mathematics and physics, “phase diagram” is used with a different meaning: a synonym for a phase space.

Common components of a phase diagram are lines of equilibrium or phase boundaries, which refer to lines that mark conditions under which multiple phases can coexist at equilibrium.

Phase transitions occur along lines of equilibrium.

Triple points are points on phase diagrams where lines of equilibrium intersect.

Triple points mark conditions at which three different phases can coexist.

For example, the water phase diagram has a triple point corresponding to the single temperature and pressure at which solid, liquid, and gaseous water can coexist in a stable equilibrium.

The solidus is the temperature below which the substance is stable in the solid state.

The liquidus is the temperature above which the substance is stable in a liquid state.

There may be a gap between the solidus and liquidus; within the gap, the substance consists of a mixture of crystals and liquid (like a “slurry”).




Unfortunately, Settled Science fails to explain [or accommodate] the observed variability in the boiling point of water.

The assumption of the sharpness of the liquid-gas boundary theoretically precludes the variability of boiling point under fixed external pressure; this means that there is no obvious way of accommodating the observed variations within the traditional physical theory.

First, it is difficult to understand the role of dissolved air in facilitating boiling; this may require some detailed molecular modelling, which the engineering theory does not provide.

Second, the lowering of the boiling temperature below the thermodynamically defined boiling point is difficult to understand.

Discussion point 3: Modern theories of boiling – Hasok Chang

Therefore, it is unsurprising that mechanical and chemical engineers do not use the Phase Diagrams produced by Settled Science.

In modern treatises on boiling in mechanical and chemical engineering, we do not find the standard thermodynamic phase diagrams.

Instead, the engineer’s paradigmatic representation of boiling is the “boiling curve”, which plots the rate of heat transfer against the degree of the “surface superheat” or the “excess temperature”.

The main independent variable in the engineering discourse is how much the temperature of the heating element exceeds the “normal” boiling point.

Therefore, in the best modern theory of boiling we have, the temperature of the water itself has no role to play!

And if we do assume that there is some degree of superheating in the first layer of water, and seek to say something about the effect of that superheating, we find that there is no theory that can be applied easily. The question cannot even be articulated in the standard physics discourse because the theory there is based on the idealized assumption that superheating never occurs.

The other main thing to note about the engineer’s boiling curve is that the main dependent variable is the rate of heat transfer.

These engineers are mainly interested in boiling as a method of carrying heat away from hot places to colder places (one can easily imagine the consequences of not understanding this correctly, in trying to keep a nuclear reactor from overheating, for example).

In that context, the temperature of the liquid water, especially well above the first layer, is distinctly of secondary interest, and is freely admitted to be quite variable depending of the situation.

The engineering treatises on heat transfer give a detailed classification of boiling behavior, largely determined by the degree of surface superheat and the configuration of the boiling setup.

Boiling Curve

Modern theories of boiling – Hasok Chang

Sadly, these issues were highlighted by Dufour 153 years ago when it became apparent that the pressure-balance theory provided a necessary but not sufficient explanation for the boiling of water.

The first great anomaly for the pressure-balance theory of boiling was the fact that the boiling temperature was plainly not fixed even when the external pressure was fixed.

The typical and reasonable thing to do was to postulate, and then try to identify the existence of interfering factors preventing the “normal” operation of the pressure-balance mechanism.

An alternate viewpoint was that the matching of the vapour pressure with the external pressure was a necessary, but not sufficient condition for boiling, so other facilitating factors had to be present in order for boiling to occur.

Marcet’s beautiful confirmations seemed to show beyond any reasonable doubt the correctness of the pressure-balance theory modified by the adhesion hypothesis.

However, two decades later Dufour (1861, 254-255) voiced strong dissent on the role of adhesion.

Since he observed extreme superheating of water drops removed from solid surfaces by suspension in other liquids, he argued that simple adhesion to solid surfaces could not be the main cause of superheating.

Instead Dufour stressed the importance of the ill-understood molecular actions at the point of contact between water and other substances:

For example, if water is completely isolated from solids, it always exceeds 100°C before turning into apour.

It seems to me beyond doubt that heat alone, acting on water without the joint action of alien molecules, can only produce its change of state well beyond what is considered the temperature of normal ebullition.

Dufour’s notion was that the production of apour would only take place when a sort of equilibrium that maintains the liquid state was broken.

Boiling was made possible at the point of pressure-balance, but some further factor was required for the breaking of equilibrium, unstable as it may be.

Heat alone could serve as the further facilitating factor, but only at a much higher degree than the normal boiling point.

Dufour also made the rather subtle point that the apour pressure itself could not be a cause of apour-production, since the apour pressure was only a property of “future apour,” which did not yet exist before boiling actually set in.

Dufour’s critique was cogent, but he did not get very far in advancing an alternative.

He was very frank in admitting that there was insufficient understanding of the molecular forces involved (see the last pages of Dufour 1861, esp. 264).

Therefore the principal effect of his work was to demolish the adhesion hypothesis without putting in a firm positive alternative.
19th century theories of boiling – Hasok Chang

Hopefully, Settled Science wont ignore these issues for another 153 years.


Gallery | This entry was posted in Books, Science, Water. Bookmark the permalink.

9 Responses to Hasok Chang: The Boiling Point Myth

  1. A C Osborn says:

    It was quite interesting that on the BBC “Cloud” experiment program they showed similar problems with freezing water.
    They demonstrated how water freezes at different temperatures depending on the types and quantities of particles in the water.
    So the question is does pure Water also Not Freeze at exactly 0 degrees C or 32 degrees F?

  2. johnsw1258 says:

    First layer of water – The structured layer ?
    Interface – Water at the interface is structured water.
    4th state of water – tiny mention but ignored mistake.
    Is every H or every O or H2O the same ? I don’t think so.
    The Universe is Electric

  3. Louis Hissink says:

    The phase diagram shows P vs T, and I wonder what the result would be if the electric field was changed in magnitude? After all, every scientific experiment is conducted within the ambient electric field of the earth’s surface but no one seems have thought about whether a change in the electric field affects physical and chemical reactions. Chemistry is, when all said and done, the behaviour of electrically charged anions and cations.

    • malagabay says:

      Like Likes Like

      Perhaps the least obvious principle is the like-likes-like attraction.

      The idea that like charges can attract one another seems counterintuitive until you recognize that it requires no violation of physical principles.

      The like charges themselves don’t attract; the attraction is mediated by the unlike charges that gather in between.

      Those unlikes draw the like charges towards one another, until like-like repulsion balances the attraction.

      Many physicists presume that like-like attraction cannot exist in spite of acceptance by some well-known physicists, including Richard Feynman.

      Richard Feynman coined the phrase “like-likes-like through an intermediate of unlikes.”

      He understood that such attraction might be fundamental to physics and chemistry.

      Nevertheless, the majority of scientists reflexively presume that like charges must always repel.

      Hardly a fleeting thought is accorded the prospect that those like charges might actually attract if unlike charges lie in between.

      The Fourth Phase of Water – 2013 – Gerald H. Pollack

      • Let me put it in another way – we live within a plasma double layer and the field strength in that layer must affect things including nuclear phenomena including radioactivity and chemical reactions. It is one EM field, however, that is ‘ignored’ in much earth science.

        (I’m familiar with Gerry Pollack’s work, by the way).

  4. Off thread a little but think about the specific heats of water phases – solid, liquid and gas. The solid and gas phases have values ~2 for specific heat. Liquid water, however, is 4; which means that it takes double the heat to raise the temperature of water 1 degree Celsius.

    Now think about Dr. Kevin Trenberth’s (IPCC climate scientist) worry over the missing heat in the oceans etc. Less comes out of the system than what goes in. Where is the missing heat?

    Well Gerry Pollack might have an explanation for that as 70% of the earth’s surface is covered by liquid water, which will have a widespread EZ layer at its surface, and which is electrically a battery.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s