Tag: phlogiston

Should we trust an experiment that suggests a stone can eat iron?

Is it poor scientific practice to explain away results we would not expect?

Keith S. Taber

how convinced would be be by a student who found an increase in mass after burning some magnesium and argued that this showed that combustion was a process of a substance consuming oxygen as a kind of food

I came across an interesting account of an experiment which seemed to support a hypothesis, but where the results were then explained away to reject the hypothesis.

An experiment to test whether a lodestone buried in iron filings will get heavier
Experimental results always need interpretation

That might seem somewhat dubious scientific practice, but one of the things that becomes clear when science is studied in any depth is that individual experiments seldom directly decide scientific questions. Not only is the common notion that a positive result proves a hypothesis correct over-simplistic, but it is also seldom the case that a single negative result can be assumed to be sufficient to reject a hypothesis. 1

Given that, the reason I thought this report was interesting is that it was published some time ago, indeed in 1600. It also put me in mind of a practical commonly undertaken in school science to demonstrate that combustion involves a substance combining with oxygen. In that practical activity (commonly mislabelled as an 'experiment' 2), magnesium metal (for example) is heated inside a ceramic crucible until it has reacted, and by careful weighing it is found (or perhaps I should say, it should be found, as it can be a challenging practical for the inexperienced) that the material after combustion weighs more than before – as the magnesium has reacted with a substance from the air (oxygen).3 This is said to give support to the oxygen theory of combustion, and to be contrary to the earlier phlogiston theory which considered flammable materials to contain a substance called phlogiston which was released during combustion (such that what remains is of less mass than before).

Testing whether lodestones eat iron

The historical experiment that put me in mind of this involved burying a type of stone known as a lodestone in iron filings. The stone and filings were carefully weighed before burial and then again some months later after being separated. The hypothesis being tested was that the weight of the lodestone would increase, and there would be a corresponding decrease in the mass of the weight of the iron filings. Apparently at the end of the experiment the measurements, strictly at least, suggested that this was what had occurred. Yet, despite this, the author presenting the account dismissed the result – arguing that it was more likely the finding was an artifact of the experimental procedure either not being sensitive enough, or not having been carried out carefully enough.

Explaining away results – in science and in school laboratories

That might seem somewhat against the spirit of science – I wonder if readers of this posting feel that is a valid move to make: to dismiss the results, as if scientists should be fee to pick and chose which results they wish to to take notice of?

But I imagine the parallel situation has occurred any number of times in science classrooms, for example where the teacher responds to students' practical demonstrations that what is left after burning magnesium has less mass than the magnesium had before. Rather than seeing this as a refutation of the oxygen hypothesis (actually now, of course, canonical theory) – and possible support for the notion that phlogiston had been released – the teacher likely explains this away as either a measurement error or, more likely, a failure to retain all of the magnesia [magnesium oxide] in the crucible for the 'after' measurement.

Hungry magnets

The historical example is discussed in William Gilbert's book about magnetism, usually known in English as 'On the magnet'. 4 This is sometimes considered the first science book, and consists of both a kind of 'literature review' of the topic, as well as a detailed report of a great many observations and demonstrations that (Gilbert claims) were original and made by Gilbert himself. There were no professional scientists in 1600, and Gilbert was a physician, a medical practitioner, but he produced a detailed and thoughtful account of his research into magnets and magnetism.

Gilbert's book is fascinating to a modern reader for its mixture of detailed accounts that stand today (and many of which the reader could quite easily repeat) alongside some quite bizarre ideas; and as an early example of science writing that mixes technical accounts with language that sometimes seems quite unscientific by today's norms – including (as well as a good deal of personification and anthropomorphism) some very unprofessional remarks about some other scholars he considers mistaken. Gilbert certainly has little time for philosophers ('philosophizers') who set out theories about natural phenomena without ever undertaking any observations or tests for themselves.

Lodestones

Magnetism has been known since antiquity. In particular, some samples of rock (usually samples of magnetite, now recognised as Fe3O4) were found to attract both each other and samples of iron, and could be used as a compass as they aligned, more or less, North-South when suspended, or when floated in water (in a makeshift 'boat'). Samples of this material, these naturally occurring magnets, were known as lodestones.

Yet the nature of magnetism, seemingly an occult power that allowed a stone to attract an iron nail, or the earth to turn a compass needle, without touching it, remained a mystery. Some of the ideas that had been suggested may seem a little odd today.

Keepers as nutrients?

So, for example, it is common practice to store magnets with 'keepers'. A horseshoe magnet usually has a steel rod placed across its ends, and bar magnets are usually stored in pairs with steel bars making a 'circuit' by connecting between the N of one magnet with the S of the other. But why?

One idea, that Gilbert dismisses is that the magnet (lodestone) in effect needs a food source to keep up its strength,

"The loadstone is laid up in iron filings, not that iron is its food; as though loadstone were alive and needed feeding, as Cardan philosophizes; nor yet that so it is delivered from the inclemency of the weather (for which cause it as well as iron is laid up in bran by Scaliger; mistakenly, however, for they are not preserved well in this way, and keep for years their own fixed forms): nor yet, since they remain perfect by the mutual action of their powders, do their extremities waste away, but are cherished & preserved, like by like."

Gilbert, 1600 – Book 1, Chapter 16.

Girolamo Cardano was an Italian who had written about the difference between amber (which can attract small objects due to static electrical charges) and lodestones, something that Gilbert built upon. However, Gilbert was happy to point out when he thought 'Cardan' was mistaken.

An experiment to see if iron filings will feed a magnet

Gilbert reports an experiment carried out by Giambattista della Porta. Porta's own account is that:

"Alexander Aphrodiseus in the beginning of his Problems, enquires wherefore the Loadstone onely draws Iron, and is fed or helped by the fillings of Iron; and the more it is fed, the better it will be: and therefore it is confirmed by Iron. But when I would try that, I took a Loadstone of a certain weight, and I buried it in a heap of Iron-filings, that I knew what they weighed; and when I had left it there many months, I found my stone to be heavier, and the Iron-filings lighter: but the difference was so small, that in one pound I could finde no sensible declination; the stone being great, and the filings many: so that I am doubtful of the truth."

Porta, 1658: Book 7, Chapter 50

Gilbert reports Porta's experiment in his own treatise, but adds potential explanations of why the iron filings had slightly lost weight (it is very easy to lose some of the material during handling), and why the magnet might be slightly heavier (it could have become coated in some material during its time buried),

"Whatever things, whether animals or plants, are endowed with life need some sort of nourishment, by which their strength not only persists but grows firmer and more vigorous. But iron is not, as it seemed to Cardan and to Alexander Aphrodiseus, attracted by the loadstone in order that it may feed on shreds of it, nor does the loadstone take up vigour from iron filings as if by a repast on victuals [i.e., a meal of food]. Since Porta had doubts on this and resolved to test it, he took a loadstone of ascertained weight, and buried it in iron filings of not unknown weight; and when he had left it there for many months, he found the stone of greater weight, the filings of less. But the difference was so slender that he was even then doubtful as to the truth. What was done by him does not convict the stone of voracity [greediness, great hunger], nor does it show any nutrition; for minute portions of the filings are easily scattered in handling. So also a very fine dust is insensibly born on a loadstone in some very slight quantity, by which something might have been added to the weight of the loadstone but which is only a surface accretion and might even be wiped off with no great difficulty."

Gilbert, 1600 – Book 2, Chapter 25.
Animistic thinking

To a modern reader, the idea that a lodestone might keep up its strength by eating iron filings seems very fanciful – and hardly scientific. To refer to the stone feeding, taking food, or being hungry, is animistic – treating the stone as though it is a living creature. We might wonder if this language is just being used metaphorically, as it seems unlikely that intelligent scholars of the 16th Century could actually suspect a stone might be alive. Yet, as Gilbert points out, there was a long tradition of considering that the lodestone, being able to bring about movement, had a soul, and Gilbert himself seemed to feel this was not so 'absurd'.

A reasonable interpretation?

We should always be aware of the magnitude of likely errors in our measurements, and not too easily accept results at the margins of what can be measured. Gilbert's suggestions for why the test of whether mass would be transferred from the iron to the magnet might have given flawed positive results seem convincing. It would be easy to lose some of the filings in the experiment: especially if the "heap of Iron-filings" was left for several months without any containment! And the lodestone could indeed easily acquire some extraneous material that needed to be cleaned off to ensure a valid weighing. As the lodestone attracts iron, all of the filings would need to be carefully cleaned from it (and returned to the 'heap' before the re-weighing).

But, I could not help but wonder if, in part at least, I found Gilbert's explaining away of the results as reasonable, simply because I found the premise of the iron acting as a kind of food as ridiculous. We should bear in mind that although the predicted change in mass was motivated by a notion of the magnet needing nutrition, that might not be the only scenario which might give rise to the same prediction. 1 After all, how convinced would be be by a student who

  • suggested combustion was a process of a substance consuming oxygen as a kind of food, and
  • therefore predicted that magnesium would be found to have got heavier after a good meal, and
  • subsequently found an increase in mass after burning some magnesium, and
  • argued that this gave strong support for the oxygen-as-food principle?

Coda

It is rather difficult for us today to really judge how language was used centuries ago. Do these natural philosophers talking of magnets eating iron mean this literally, or is it just figurative – intended as a metaphor that readers would understand suggested that there was a process somewhat akin to when a living being eats? 5 Some of them seemed quite serious about assigning souls to entities we today would conspire obviously inanimate. But we should be careful of assuming apparently incredible language was meant, or understood, literally.

In the same week as I was drafting this posting I read an article in Chemistry World about how the heavier elements are produced, which quoted Professor Brian Metzer, physicist at Columbia University,

"What makes the gamma-ray burst in both of these cases [merging neutron stars and the collapse of large rapidly rotating stars] is feeding a newly-formed black hole matter at an extremely high rate…The process that gives rise to the production of this neutron-rich material is actually outflows from the disc that's feeding the black hole."

Brian Metzer quoted in Wogan, 2022

If we would be confident that Professor Metzer meant 'feeding a black hole' to be understood figuratively, we should be careful to reserve judgement on how the feeding of lodestones was understood when Porta and Gilbert were writing.

Sources cited:
Notes:

1 Strictly scientific tests never 'prove' or 'disprove' anything.

The notion of 'proof' is fine in the context of purely theoretical disciplines such as in mathematics or logic, but not in science which tests ideas empirically. Experimental results always underdetermine theories (that is, it is always possible to think up other theories which also fit the results, so a result never 'proves' anything). Apparently negative results do not refute ('disprove') a theory either, as any experimental test of a hypothesis also depends upon other factors (Has the researcher been sloppy? Is the measuring instrument valid – and correctly calibrated? Are any simplifying assumptions reasonable in the context…). So experimental results offer support for, or bring into question, specific theoretical ideas, without ever being definitive.

2 An experiment is undertaken to test a hypothesis. Commonly in school practical work 'experiments' are carried out to demonstrate an accepted principle, such that it is already determined what the outcome 'should' be – students may have already been told the expected outcome, it appears i n their textbooks, and the title of the activity may be suggestive ('to show that mass increases on combustion'). Only if there is a genuine uncertainty about the outcome should the activity be labelled an experiment – e.g., it has been suggested that combustion is like the fuel eating oxygen, in which case things should be heavier after burning – so let's weigh some magnesium, burn it, and then re-weight what we have left (dephlogisticated metal?; compound of metal with oxygen?; well-fed metal?)

3 Mass and weight are not the same thing. However, in practice, measurements of weight made in the laboratory can be assumed as proxy measurements for mass.

4 As was the norm in European scholarship at that time, Gilbert wrote his treatise in Latin – allowing scholars in different countries to read and understand each other's work. The quotations given here are from the 1900 translation into English by S.P. Thompson.

5 Such metaphors can act as communication tools in 'making the unfamiliar familiar' and as thinking tools to help someone pose questions (hypotheses?) for enquiry. There is always a danger, however, that once such figures of speech are introduced they can channel thinking, and by providing a way of talking about and thinking about some phenomena they can act as obstacles to delving deeper in their nature (Taber & Watts, 1996).

Learning about natural selection and denying evolution

An ironic parallel

Keith S. Taber

Image by Free-Photos from Pixabay 

I was checking some proofs for something I had written today* [Taber, 2017], and was struck by an ironic parallel between one of the challenges for teaching about the scientific theory of evolution by natural selection and one of the arguments put forward by those who deny the theory. The issue concerns the value of having only part of an integrated system.

The challenge of evolutionary change

One of the arguments that has long been made about the feasibility of evolution is that if it occurs by many small random events, it could not lead to progressive increases in complexity – unless it was guided by some sense of design to drive the many small changes towards some substantive new feature of ability. So, for example, birds have adaptations such as feathers that allow them to fly, even though they are thought to have evolved from creatures that could not fly. The argument goes that for a land animal to evolve into a bird there need to be a great many coordinated changes. Feathers would not appear due to a single mutation, but rather must be the result of a long series of small changes. Moreover, simply growing features would not allow an animal to fly without other coordinated changes such as evolving very light bones and changes in anatomy to support the musculature needed to power the wings.  

The same argument can be made about something like the mammalian eye, which can hardly be one random mutation away from an eyeless creature. The eye requires retinal cells, linked to the optic nerve, a lens, the iris, and so on. The eye is an impressive piece of equipment which is as likely to be the result of a handful of random events, as would be – say, a pocket watch found walking on the heath (to use a famous example). A person finding a watch would not assume its mechanism was the result of a chance accumulation of parts that had somehow fallen together. Rather, the precise mechanism surely implies a designer who planned the constructions of the overall object. In 'Intelligent Design' similar arguments are made at the biochemical level, about the complex systems of proteins which only function after they have independently come into existence and become coordinated into a 'machine' such as a flagellum.  

The challenge of conceptual change

The parallel concerns the nature of conceptual changes between different conceptual frameworks. Paul Thagard (e.g., 1992) has looked at historical cases and argued that such shifts depend upon judgements of 'explanatory coherence'. For example, the phlogiston theory explained a good many phenomena in chemistry, but also had well-recognised problems.

The very different conceptual framework developed by Lavoisier [the Lavoisiers? **] (before he was introduced to Madame Guillotine) saw combustion as a chemical reaction with oxygen (rather than a release of phlogiston), and with the merits of hindsight clearly makes sense of chemistry much more systematically and thoroughly. It seems hard now to understand why all other contemporary chemists did not readily switch their conceptual frameworks immediately. Thagard's argument was that those who were very familiar with phlogiston theory and had spent many years working with it genuinely found it had more explanatory coherence than the new unfamiliar oxygen theory that they had had less opportunity to work with across a wide range of examples. So chemists who history suggests were reactionary in rejecting the progressive new theory were actually acting perfectly rationally in terms of their own understanding at the time. ***

Evolution is counter-intuitive

Evolution is not an obvious idea. Our experience of the world is of very distinct types of creatures that seldom offer intermediate uncertain individuals. (That may not be true for expert naturalists, but is the common experience.) Types give rise to more of their own: young children know that pups come from dogs and grow to be adult dogs that will have pups, and not kittens, of their own. The fossil record may offer clues, but the extant biological world that children grow up in only offers a single static frame from the on-going movie of evolving life-forms. [That is, everyday 'lifeworld' knowledge can act as substantial learning impediment – we think we already know how things are.]

Natural selection is an exceptionally powerful and insightful theory – but it is not easy to grasp. Those who have become so familiar with it may forget that – but even Darwin took many years to be convinced about his theory.

Understanding natural selection means coordinating a range of different ideas about inheritance, and fitness, and random mutations, and environmental change, and geographical separation of populations, and so forth. Put it all together and the conceptual system seems elegant – perhaps even simple, and perhaps with the advantage of hindsight even obvious. It is said that when Huxley read the Origin of Species his response was "How extremely stupid not to have thought of that!" That perhaps owes as much to the pedagogic and rhetorical qualities of Darwin's writing in his "one long argument". However, Huxley had not thought of it. Alfred Russel Wallace had independently arrived at much the same scheme and it may be no coincidence that Darwin and Wallace had both spent years immersing themselves in the natural history of several continents.   

Evolution is counter-intuitive, and only makes sense once we can construct a coherent theoretical structure that coordinates a range of different components. Natural selection is something like a shed that will act as a perfectly stable building once we have put it together, but which  it is very difficult to hold in place whilst still under construction. Good scaffolding may be needed. 

Incremental change

The response to those arguments about design in evolution is that the many generations between the land animal and the bird, or the blind animal and the mammal, get benefits from the individual mutations that will collectively, ultimately lead to the wing or mammalian eye. So a simple eye is better than no eye, and even a simple light sensitive spot may give its owner some advantage. Wings that are good enough to glide are useful even if their owners cannot actually fly. Nature is not too proud to make use of available materials that may have previously had different functions (whether at the level of proteins or anatomical structures). So perhaps features started out as useful insulation, before they were made use of for a new function. From the human scale it is hard not to see purpose – but the movie of life has an enormous number of frames and, like some art house movies, the observer might have to watch for some time to see any substantive changes. 

A pedagogical suggestion – incremental teaching?

So there is the irony. Scientists counter the arguments about design by showing how parts of (what will later be recognised as) an adaptation actually function as smaller or different advantageous adaptations in their own right. Learning about natural selection presents a situation where the theory is only likely to offer greater explanatory coherence than a student's intuitive ideas about the absolute nature of species after the edifice has been fully constructed and regularly applied to a range of examples.

Perhaps we might take the parallel further. It might be worth exploring if we can scaffold learning about natural selection by finding ways to show students that each component of the theory offers some individual conceptual advantages in thinking about aspects of the natural world. That might be an idea worth exploring. 

(Note. 'Representing evolution in science education: The challenge of teaching about natural selection' is published in B. Akpan (Ed.), Science Education: A Global Perspective. The International Edition is due to be published by Springer at the end of June 2016.)

Notes:

* First published 30th April 2016 at http://people.ds.cam.ac.uk/kst24/

** "as Madame Lavoisier, Marie-Anne Pierrette Paulze, was his coworker as well as his wife, and it is not clear how much credit she deserves for 'his' ideas" (Taber, 2019: 90). Due to the times in which they works it was for a long time generally assumed that Mme Lavoisier 'assisted' Antoine Lavoisier in his work, but that he was 'the' scientist. The extent of her role and contribution was very likely under-estimated and there has been some of a re-evaluation. It is known that Paulze contributed original diagrams of scientific apparatus, translated original scientific works, and after Antoine was executed by the French State she did much to ensure his work would be disseminated. It will likely never be know how much she contributed to the conceptualisation of Lavoisier's theories.

*** It has also been argued (in the work of Hasok Chang, for example) both that when the chemical revolution is considered, little weight is usually given to the less successful aspects of Lavoisier's theory, and that phlogiston theory had much greater merits and coherence than is usually now suggested.

Sources cited:
  • Taber, K. S. (2017). Representing evolution in science education: The challenge of teaching about natural selection. In B. Akpan (Ed.), Science Education: A Global Perspective (pp. 71-96). Switzerland: Springer International Publishing
  • Taber, K. S. (2019). The Nature of the Chemical Concept: Constructing chemical knowledge in teaching and learning. Cambridge: Royal Society of Chemistry.
  • Thagard, P. (1992). Conceptual Revolutions. Oxford: Princeton University Press.