Tag: combustion

Burning is when you are burning something with fire …

Iconic chemical triangles

Keith S. Taber

Derek was a participant in the Understanding Science Project. When I interviewed Derek soon after the start of his secondary schooling, he told me he liked science, and was currently studying 'burning'.

So, I asked him what that was:

What is burning?

[pause, c.2s]

When [pause, c.2s] a fuel, oxygen and heat gets – in, erm, I'm not quite sure how to explain, but it's like – you get the triangle of fire, and then, burning is just when you've got fire and you're burning something with it.

Okay, so you'd recognise it if you saw it, would you?

Yeah.

Yeah, but maybe it's not that easy to explain?

Yeah.

The notion that 'burning is just when you've got fire and you're burning something with it' – might be considered tautological:

  • burning is when you are burning something

Scientists look to explain natural phenomena with theories, principles, models, and so forth. But for most people, phenomena that they have been familiar with since very young (such as a dropped object falling) do not seem to need explanation – as they are seen as just natural events (Watts & Taber, 1996).

Derek knew about the fire triangle, but his response reminded me of another triangle that is often referred to by science educators.

Johnstone's triangle

For many years Prof. Alex Johnstone (1930-2017) worked at the Centre for Science Education that he founded at the University of Glasgow; where he undertook, supervised, and collaborated on, a good many projects in science education – especially, but not only, relating to the teaching and learning of chemistry and physics in higher education.

However, one of Johnstone's most influential publications must be the short article he published in the School Science Review (Johnstone, 1982) – the secondary science journal of the Association for Science Education. In this short piece he argued that in each of biology, chemistry, and physics, learning difficulties in part derived from how the subject was taught at several 'levels' at once, asking young learners to think simultaneously on different planes as it were. In each of these science subjects, this could be represented by a triangle. In many lessons students would be asked to think about, and inter-relate, considerations from the viewpoints of several vertices.

Johnston's chemistry triangle distinguished between three levels:

  • the macroscopic (the scale at which people observe and handle materials);
  • the submicroscopic (molecular) scale at which many chemical explanations are developed;
  • the symbolic level – where abstract symbols are used to represent the chemistry

"Those of us who are academic chemists can view our subject on at least three levels.

There is the level at which which we can see and handle materials, and describe their properties in terms of density, flammability, colour and so on. We are also interested in the possibility of conversion of one material into another with consequent changes in properties.

A second level is the representational one in which we try to represent chemical substances by formulae and their changes by equations. This is part of the sophisticated language of the subject.

The third level is atomic and molecular, a level at which we attempt to explain why chemical substances behave the way they do. We invoke atoms, molecules, ions, structures, isomers, polymers etc to give us a mental picture by which to direct our thinking and rationalize the descriptive level mentioned above.

These levels could be called (a) descriptive and functional, (b) representational, (c) explanatory. Trained chemists jump freely from level to level in a series of mental gymnastics. It is eventually very hard to separate these levels."

Johnstone, 1982 (added emphasis)

Over the years there have been many attempts to apply, elaborate, and refine Johnston's triangle, and it has been an idea that has proved very productive in thinking about learning difficulties in the subject.

"Chemistry seeks to provide qualitative and quantitative explanations for the observed behaviour of elements and their compounds. Doing so involves making use of three types of representation: the macro (the empirical properties of substances); the sub-micro (the natures of the entities giving rise to those properties); and the symbolic (the number of entities involved in any changes that take place). Although understanding this triplet relationship is a key aspect of chemical education, there is considerable evidence that students find great difficulty in achieving mastery of the ideas involved…" (Publisher's description)

One well-respected, edited, scholarly book ('Multiple Representations in Chemical Education' – Gilbert & Treagust, 2009) consisted of contributions exploring implications of the idea. Indeed, now, there is even a book entitled 'The Johnstone Triangle' (Reid, 2021) with the telling subtitle: 'the key to understanding chemistry'!

Johnstone's triangle is now the subject of a book

Reconceptualisation

Derek was just being introduced to burning as a science topic, and for him it was still just a familiar phenomenon rather than a theoretical construct. We have all seen fires, and can recognise when something is burning – but how many people really know what fire is?1 Burning and fire are everyday concepts – fire is an impressive phenomenon to a young child: one that is salient enough to be noticed. The child's brain then recognises different instances of fire as being similar and it abstracts a spontaneous concept – that there is a category of events in the world that appear like this.

Of course, the brain of the young child does this without using language (it forms a category of events in the sense that it readily recognises new instances – it does not yet have access to have technical notions of 'category', 'concept', 'abstraction' of course.) And the child does not instinctively know this is called 'fire' or 'el incendio' or 'l' incendie' or whatever, until someone who is a more mature member of the child's natural language community shares this label.2

School science will involve learning that there is a formal scientific concept3 called 'combustion' that is basically the chemist's name for burning. However, 'combustion' is a technical term, so combustion will be defined in terms of other concepts. So, whereas in everyday life we recognise what counts as a fire or burning using the brain's inherent pattern-recognition mechanism (a spontaneous conception), in chemistry we have a technical definition (a scientific concept defined in relation to to other scientific concepts, and so 'theoretical').

That is, in everyday life, if you told someone you saw something on fire, it is unlikely anyone (leaving aside science teachers) would ask you which criteria you used to know this: you did not deliberate on the matter, you simply saw, and instantly recognised, a fire. When you refer to a fire, the other person recognises what you mean because they have learnt 'fire' to be the label for their own spontaneously formed conception that allows their perceptual-cognitive system to instantly recognise a fire.

But, for a chemist, combustion is one class of chemical reaction (so the learner can only understand combustion in chemical terms if they have an appreciation of what a chemical reaction is), which only makes sense to someone who has reasonable idea what a scientist means by a substance, as chemical reactions are changes resulting in different substances. Here we have shifted from everyday notions to the theoretical descriptions of science.

In school chemistry, everyday phenomena (e.g., burning) are reconsolidated in terms of technical concepts and language (e.g., combustion). (From Taber, 2013)

The invisible nanoscopic world

But chemists are seldom satisfied with macroscopic accounts – even when posed in technical language. Rather, students will be taught to explain the observable macroscopic phenomena in terms of invisible entities which have unfamiliar properties. Imagined entities such as molecules4, nanoscopic systems which are best understood as fuzzy balls of fields – that have no actual surface, and are mostly tenuous 'clouds' of charge. (Molecules are sometimes modelled as if billiard balls, or sets of balls connected by sticks, but this is just an attempt to represent entities quite unlike the familiar referents available to learners in ways they can make sense of.)

That is, combustion will be explained as a rearrangement of electrons and atomic cores that changes one set of molecules (of the reactants in the reaction) into another (the products). This process will involve energy changes, due to differences in stability of different sets of molecules, and will progress through the breaking and making of chemical bonds.

If the learner is able to form a mental image of (i.e., imagine) chemical reactions at the nanoscopic level, and see how this can be used to explain an actual observable phenomenon (such as a fire), they then also have to learn how chemists often represent these ideas in what is in effect a specialist language – involving chemical formulae, and reaction equations, and the like.

So, when Derek was using a Bunsen burner to set fire to pasta and (not quite set fire to) raisins as he reported to me, he was using a chemical reaction that might be summarised by the chemist or science teacher as:

CH4 + 2O2 ➞ CO2 + 2H2O

Johnstone suggested that the symbolic representation was the third level, alongside the macroscopic and submicroscopic. He was absolutely right that it added to the 'learning demand'. However, there is another complication in that many of these key representations (the formulae and equations) are ambiguous as they can represent either the macroscopic level of substances weighed out in grammes (2O2 would represent 64 g of the substance oxygen, although as it is a gas it would normally be measured by volume) or the individual imagined entities of the molecular world (where 2O2 would mean two molecules of oxygen).

Useful ambiguity

This is useful ambiguity for the chemist – but an added complication for the learner who has to follow the teacher's transitions where one moment a symbol reflects a test tube of stuff, and the next some molecule. Because of its role in bridging between the two very different scales at which we explain chemistry I prefer to see these symbols as being along one side of the triangle (whilst separating out the everyday phenomenological level from the technical, theoretical descriptions used by science). However, whatever version of Johnstone's triangle is applied, it has become something of an iconic image in chemistry education.

The chemist's triplet: a variation on Johnstone's triangle (from Taber, 2013)

Another iconic triangle

Derek had not yet been introduced to all this, and he was still operating with burning as a phenomenon:

And why is this important, do you think? Why do you think we study burning?

[pause, c.2s]

I'm not sure.

No one's told you that?

No.

Is it fun, is it a fun topic?

Yeah.

What Derek did seem to have learned well was the fire triangle.

But you have this 'triangle of fire'. So does that mean that fire is always a triangular shape?

No.

So, what's a triangle of fire?

You need three things to make a fire, which is oxygen, heat and fuel.

Okay, so what if I had erm some fuel and some heat, but I didn't have any oxygen, but maybe I've got lots of fuel?

No – wouldn't have fire.

I can't have extra fuel instead?

No.

No?

You need the three things.

What if I've got lots and lots of fuel, and lots and lots of oxygen, but it's very, very cold?

No.

No, that won't work either. So I always have to have the three things?

Yeah.

Derek stuck to his claim – you always needed all three. This is a useful heuristic (useful if ever one is faced with a fire as it tells you can act by just removing one of the three essentials) even if (like most heuristics) it will sometimes fail, e.g.

  • some materials will continue burning in the absence of an external supply of oxygen as they have an internal source;
  • chlorine will support combustion in place of oxygen (but that's seldom a practical issue in everyday situations) ;
  • substances have an auto-ignition temperature (where they can spontaneously ignite), and for a few substances this is around or below room temperature;

These exceptions do not undermine the general utility of the' 'triangle'.

Some useful learning had gone on here – and potentially not just about fire, because the idea that one factor may be limiting on a process is a generally useful principle (e.g., plants grown in a soil depleted in potassium will not thrive, no matter how much sunlight, water, nitrate and phosphate is present).

But the fire triangle, even if it is not supported by a deep understanding of chemical principles, is worth teaching because of its practical value. It seems to offer a heuristic that people accept and recall. And rather like Johnston's triangle, it seems to have become rather iconic. At least, I assume that is why when COVID-19 infection rates were high, the fire triangle was used as a familiar analogy to persuade people to avoid the 'oxygen' of social mixing…

"I like to think of COVID as a fire, if we are the fuel, social mixing is the oxygen that allows the fuel to burn…'"

Read 'COVID is like a fire because…'

Work cited
Notes

1 It has been mooted that fire should be understood as an example the 'fourth' phase of matter, plasma – that is an ionised gas.5 But actually fire is more complicated than this as it contains a mixture of reactant and product molecules and the molecular fragments that form intermediate and/or transition states. Some chemical reactions, when studied at the molecular level, largely follow a single reaction path. But combustion tends to be much more complex with multiple pathways involving many different ions and molecular fragments.

Read: The states of (don't) matter? Which state of matter is fire?

So, fire is a multiphase mixture, more akin to a solution, aerosol, or suspension, than to a gas or plasma.

2 The child does not know this is called fire, and when she is told this she may not realise that such names are social conventions – according to Jean Piaget's research young children may assume that things in the world have (that is, have always had) a name that people have had to learn.

This childish idea reflects superstitious notions about names that are part of some magical systems of knowledge – 'the law of names': the idea that if you know a person or thing's real name this gives you over over them/it.

3 A very influential theory due to Lev Vygotsky takes the distinction between spontaneous concepts formed automatically, and formal taught concepts that are shared through social interaction (such as teaching). These latter kinds of concepts are usually translated from Vygotsky's Russian as 'scientific' though this is meant in the broad sense of any formal field of study. A key point emphasised by Vygotsky was that, assuming the learners could relate a taught concept to existing spontaneous concepts (that is, 'meaningful learning' occurred), they would actually come to operate with a concept which was a hybrid developed from the interaction of the intuitive understanding and the learned technically defined notion – a melded conception.

4 By referring to molecules and ions and electrons as imagined entities, I am not suggesting they are only imaginary. Most (if not all) scientists today see them as real things (even if strictly our evidence is indirect, and they arguably remain theoretical constructs). But a teacher cannot directly show the class a molecule or an electron, even if some types of imaging equipment do now produce representations of individual atoms. For the learners (and I would suggest even the teacher) these are only ever imagined entities. Yet, we expect students to do a good deal of thinking about, and with, these imagined entities.

5 If we are expanding the three states of matter, then there is an argument for making plasma the 5th phase:

  • Bose-Einstein condensates
  • solids
  • liquids
  • gases
  • plasma
  • (quark 'soups'?)

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).

COVID is like a fire because…

Keith S. Taber

Dampening down COVID? (Image by Iván Tamás from Pixabay)

Analogy in science

Analogy is a common technique used in science and science education. In scientific work analogy may be used as a thinking tool useful for generating hypotheses to explore – "what if X is like Y, then that might mean…". That is, we think we understand system Y, so, if for a moment we imagine that system X may be similar, then by analogy that would mean (for example) that A may be the cause of B, or that if we increase C then we might expect D to decrease… Suggesting analogies has been used as a way of introducing a creative activity into school science (Taber, 2016).

Read about analogies in science

Scientists also sometimes use analogies to explain their ideas and results to other scientists. However, analogies are especially useful in explaining abstract ideas to non-experts, so they are used in the public communication of science by comparing technical topics with more familiar, everyday ('lifeworld') phenomena. In the same way, teachers use analogies as one technique for 'making the unfamiliar familiar' by suggesting that the unfamiliar curriculum focus (the target concept to be taught) is in some ways just like a familiar lifeworld phenomena (the analogue or source concept).

Read about science in public discourse and the media

Read about making the unfamiliar familiar

COVID is like a fire…

So, I was interested to hear Prof. Andrew Hayward, Professor of Infectious Disease Epidemiology and Inclusion Health Research at UCL (University College London), being interviewed on the radio and suggesting that COVID was like a fire:

"Sometimes I like to think of, you know, COVID as a fire, if we are the fuel, social mixing is the oxygen that allows the fuel to burn, vaccines the water that stops the fuel from burning, and COVID cases are the sparks that spread the fire. So, we are doing well on vaccines, but there's lots of dried wood left."

There's quite a lot going on in that short statement. If Prof. Hayward had stopped at "sometimes I like to think of COVID as a fire" this would have been a simile where it is simply observed that one thing is conceived as being a bit like another.

Simile offers a comparison and leaves the listener or reader to work out the nature of the similarity (whereas metaphor, where one thing is described to be another, an example would be 'COVID is a fire',  leaves the audience to even appreciate a comparison is being made). Analogy goes further, as it makes a comparison between two conceptual structures (two systems), such that by mapping across them we can understand how the structure of the unfamiliar is suggested to be like the more familiar structure.

That is, there is a mapping (see the figure below) that is based on pairings across the analogy. Here fire and COVID disease are each treated as systems with components that are structured in a parallel way:

COVID (illness): fire
people: fuel
social mixing: oxygen
vaccines: water
COVID cases: sparks

A graphic representation of Prof. Hayward's use of analogy

A lot of us are like kindling

Moreover, having set up this analogy, we are offered some additional information – we are doing well on vaccines (= there is plenty of water to stop fuel burning), but there is still a lot of dried wood. The listener has to understand that the dry wood refers to fuel, and this maps (in the analogy) onto lots of people who can still become infected.

I suspect most people (science teachers perhaps excepted) listening to this interview will not have even explicitly noticed the nature of the analogy, but rather automatically processed the comparison. They would have understood the message about COVID through the analogy, rather than having to actively analyse the analogy itself.

We can stop the sparks spreading the fire

Professor Hayward was asked about contact tracing and suggested that

"…the key thing is the human discussion with somebody who has COVID to identify who their contacts are and to ask them to isolate as well, and that really stops those sparks getting into the population and really helps to dampen down the fire."

That is, that potential COVID cases (that are like sparks in the fire system) can be prevented from mixing with the wider population (who are like fuel in the fire system) and this will dampen down the fire (the illness in the COVID system). {Note 'dampen down' seems to be a metaphor here rather than a true part of the analogy (in which it is the vaccines that have the effect of 'literally' {analogously} dampening down the fire). Stopping sparks mixing with fuel will limit new areas of combustion starting rather than dampening down the existing fire.}

An argument about contact tracing made using the analogy

Again, most people listening to this would likely have taken on board the intended meaning quite automatically, without having to deliberately analyse this answer – even though the response shifts between the target topics (the COVID disease system) and the analogue (the fire system) – so the sparks (fire system – equivalent to infectious cases) are stopped from getting into the population (COVID system – equivalent to the fuel supply).

This is reminiscent of chemistry teaching which slips back and forth between macroscopic and molecular levels of description – and so where references to, for example, hydrogen could mean the substance or the molecule – and the same word may have a different referent at different points in the same utterance (Taber, 2013). Whether this is problematic depends upon the past experiences of the listener – someone with extensive experience of a domain (probably most of the audience of a serious news magazine programme understand enough about combustion and infection to not have to deliberate on the analogy discussed here) can usually make these shifts automatically without getting confused.

Fire requires…AND…AND…

An analogy can only be effective when the analogue is indeed more familiar to the audience (you cannot make the unfamiliar familiar by comparing an unfamiliar target with an analogue that is also unfamiliar) so the use of the analogy by Professor Hayward assumed some basic knowledge about fire. Indeed it seemed to assume knowledge of the so-called 'fire triangle'.

Three factors are need to initiate/maintain combustion: fire may be stopped by removing one or more of these.

This is the idea that for a fire to commence or continue there need to be three things: something combustible to act as fuel; AND oxygen (or another suitable substance – as when iron filings burn in chlorine – but in usual circumstances it will be oxygen); AND a source of energy sufficient to initiate reaction (as burning is exothermic, once a fire is underway it may generate enough heat to maintain combustion – and sparks may spread the fire to nearby combustible material). To extinguish a fire, one needs to remove at least one of these factors – water can act as a heat sink to decrease the temperature, and may also reduce the contact between the fuel and oxygen. Preventing sparks from transferring hot material that can initiate further sites of combustion (providing energy to more fuel) can also be important.

Unobtrusive pedagogy

The quotes here were part of a short interview with a broadcast journalist and intended for a general public audience. Prof. Hayward introduced and developed his analogy as just sharing a way of thinking, and indeed analogy is such a common device in conversation that it was not obviously marked as a pedagogic technique. However, when we think about how such a device works, and what is expected of the audience to make sense of it, I think it is quite impressive how we can often 'decode' and understand such comparisons without any conscious effort. Providing, of course, that the analogue is indeed familiar, and the mapping across the two conceptual structures can be seen to fit.

Works cited:

Taber, K. S. (2013). Revisiting the chemistry triplet: drawing upon the nature of chemical knowledge and the psychology of learning to inform chemistry education. Chemistry Education Research and Practice, 14(2), 156-168. doi:10.1039/C3RP00012E

Taber, K. S. (2016). 'Chemical reactions are like hell because…': Asking gifted science learners to be creative in a curriculum context that encourages convergent thinking. In M. K. Demetrikopoulos & J. L. Pecore (Eds.), Interplay of Creativity and Giftedness in Science (pp. 321-349). Rotterdam: Sense. (Download the author's manuscript version of this chapter.)

 

We can't handle the scientific truth

"If the muscles and other cells of the body burn sugar instead of oxygen…"

Do they think we cannot handle the scientific truth?

I should really have gone to bed, but I was just surfing the channels in case there was some 'must watch' programme I might miss, and I came across a screening of the film 'A few good men'. This had been a very popular movie at one time, and I seem to recall watching it with my late wife. I remembered it as an engaging film, and as an example of the 'courtroom drama' genre: but beyond that I could really only remember Tom Cruise as defence advocate questioning Jack Nicholson's as a commanding officer – and the famous line from Nicholson – "You can't handle the truth!".

This became something of a meme – I suspect now there are a lot of people who 'know' and use that line, who have never even seen the film and may not know what they are quoting from.

So, I  though I might watch a bit, to remind myself what the actual case was about. In brief, a marine stationed at the U.S. Guantánamo Bay naval base and detention camp had died at the hands of two of his comrades. They had not intended to kill, but admitted mistreating him – their defence was they were simply obeying orders in subjecting a colleague who was not measuring up, and was letting the unit down, to some unpleasant, but ultimately (supposedly) harmless, punishment.

The film does not contain a lot of science, but what struck me was the failure to get some science that was invoked right.  I was so surprised at what I thought I'd heard being presented as science, that I went back and replayed a section, and I then decided to see if I  could find the script (by Aaron Sorkin*, screenplay adapted from his own theatre play) on the web, to see if what was said had actually been written into the script.

One of the witnesses is a doctor who is asked by the prosecuting counsel to explain lactic acidosis.

Burning sugar instead of oxygen?

The characters here are:

Capt. Jack Ross (played by Kevin Bacon) the prosecuting counsel,

Dr. Stone (Christopher Guest) and

 

 

 

Lt. Daniel Kaffee (Cruise's character).

On direct examination:

Ross: Dr. Stone, what's lactic acidosis?

Stone: If the muscles and other cells of the body burn sugar instead of oxygen, lactic acid is produced. That lactic acid is what caused Santiago's lungs to bleed.

Ross: How long does it take for the muscles and other cells to begin burning sugar instead of oxygen?

Stone: Twenty to thirty minutes.

Ross: And what caused Santiago's muscles and other cells to start burning sugar? [In the film, the line seems to be: And what caused this process to be speed up in Santiago's muscles?]

Stone: An ingested poison of some kind.

Later, under cross-examination

Kafee: Commander, if I had a coronary condition, and a perfectly clean rag was placed in my mouth, and the rag was accidentally pushed too far down, is it possible that my cells would continue burning sugar after the rag was taken out?

Stone: It would have to be a very serious condition.

What?

If a student suggested that lactic acid is produced when the muscles burn sugar instead of oxygen we would likely consider this an alternative conception (misconception). It is, at best, a clumsy phrasing, and is simply wrong.

Respiration

Metabolism is a set of processes under very fine controls, so whether we should refer to metabolism as burning or not, is a moot point. Combustion tends to be a vigorous process that is usually uncontrolled. But we can see it as a metaphor: carbohydrates are 'burnt' up in the sense that they undergo reactions analogous to burning.

But burning requires oxygen (well, in the lab. we might burn materials in chlorine, but, in general, and in everyday life, combustion is a reaction with oxygen), so what could burning oxygen mean?

In respiration, glucose is in effect reacted with oxygen to produce carbon dioxide and water. However, this is not a single step process, but a complex set of smaller reactions – the overall effect of which is

glucose + oxygen → carbon dioxide + water

Breaking glucose down to lactic acid also acts as an energy source, but is no where near as effective. Our muscles can undertake this ('anaerobic') process when there is insufficient oxygen supply –  for example when undertaking high stamina exercise – but this is best seen as a temporary stop-gap, as lactic acid build up causes problems (cramp for example) – even if not usually death.

Does science matter?

Now clearly the science is not central to the story of 'A few good men'. The main issues are (factual)

  • whether the accused men were acting under orders;

(ethical)

  • the nature of illegal orders,
  • when service personal should question and ignore orders (deontology) given that they seldom have the whole picture (and in this film one of the accused men is presented as something of a simpleton who viewer may suspect should not be given much responsibility for decision making),
  • whether it is acceptable to use corporal or cruel punishment on an under-performing soldier (or marine) given that the lives of many may depend upon their high levels of performance (consequentialism, or perhaps pragmatics)…

There is also a medical issue, regarding whether the torture of the soldier was the primary cause of death, or whether there was an underlying health issue which the medical officer (Stone) had missed and which might also explain the poor performance. [That is a theme which featured large in a recent very high profile real murder case.]

Otherwise the film is about the characters of, and relationships among, the legal officers. Like most good films – this is film about people, and being human in the world, and how we behave towards and relate to each other.

The nature of lactic acidosis is hardly a key point.

But if it is worth including in the script as the assumed cause of death, and its nature relevant – why not get the science right?

Perhaps, because science is complicated and needs to be simplified for the cinema-goer who, after all, wants to be entertained, not lectured?

Perhaps there is no simple account of lactic acidosis which could be included in the script without getting technical, and entering into a long and complicated explanation.

In teaching science…

But surely that is not true. In teaching we often have to employ simplifications which ignore complexity and nuance for the benefit of getting the core idea across to learners. We seek the optimal level of simplification that learners can make good sense of, but which is true to the core essence of the actual science being discussed (it is 'intellectually honest') and provides a suitable basis for later more advanced treatments.

It can be hard to find that optimum level of simplification – but I really do not think that explaining lactic acidosis as burning sugar instead of oxygen could be considered a credit-worthy attempt.

Dr. Stone, can we try again?

What about, something like:

Dr. Stone, what's lactic acidosis?

It occurs when the body tissues do not have sufficient oxygen to fully break down sugar in the usual way, and damaging lactic aid is produced instead of carbon dioxide and water.

I am sure there are lots of possible tweaks here. The point is that the script did not need to go into a long medical lecture, but by including something that was simply nonsensical, and should be obviously wrong to anyone who had studied respiration at school (which should be everyone who has been to school in the past few decades in many countries), it distracts, and so detracts, from the story.

All images from 'A few good men' (1992, Columbia Pictures)

 

 

 

 

 

 

 

 

 

 

* I see that ("acclaimed screenwriter") Aaron Sorkin is planning a new live television version of 'A Few Good Men' – so perhaps the description of lactic acidosis can be updated?

I could not have been born to different parents…

A reflection on free will, determinism, justice, ignorance, and identity

Keith S. Taber

www.abc.net.au

This morning I listened to a really interesting podcast on 'Free will, retribution and just deserts', with Prof. Gregg D. Caruso being interviewed about his ideas by David Rutledge.

The question of free will (as opposed to a rigid determinism) is one of those matters that most people seem to instinctively feel they know the answer to: we all feel we have free will. Why did I decide to write this blog rather than do something else this evening? Clearly I think that I freely decided to do this because this was something I wanted to do. Yet, that it feels like a free choice, means little. We may also think that life would lack any meaning in the absence of free will, and that being free agents is a much more attractive proposition; but wanting something to be the case is not much of an argument for thinking it is so.

If everything is predetermined (perhaps by the initial conditions of the big bang plus the fixed laws of the universe) then those people who think they have free will must have no choice but to think so (as it was determined), just as those who (correctly, in this scenario) reject free will cannot be given credit for this insight. (Actually, I doubt anyone really believes that they do not have free will, not even any off-duty philosophers, as I am not sure how one can live one's life that way – as just an observer of the automaton that others identify with you, as a viewer of the unfolding movie that is your life?)

Image by jraffin from Pixabay
How much is ending up here an accident of birth rather than the outcome of deliberate 'free' choices? (Image by jraffin from Pixabay)

I found much of Caruso's argument convincing, in particular in relation to the justification of judicial incarceration. My moral instincts are that if the state takes away someone's liberty this should be because it is acting to protect society or its vulnerable members, and not as an act of retribution.

Caruso argued that we should take note of how so many people in the prison system have mental health issues or addictions, and he pointed to the strong associations between convictions and poverty or other limiting or damaging socio-economic conditions. This raises issues of social justice, and when treatment and rehabilitation are more productive responses to crime than punishment per se. Caruso was primarily using the example of the situation in the United States, where he suggested most inmates have mental health issues, but his general points apply more widely.

The lottery of life

However, there was one point at which I became uneasy with the argument, where Caruso brought in what is sometimes referred to as the "there, but for the grace of God, go I" position. If we accept that people born in poverty and squalor, or brought up in neglect or abuse, are those most likely to enter the criminal justice system as offenders, then those of us fortunate enough to have been born into relative privilege should acknowledge how lucky we were in the lottery of life, for "there, there, but for the grace of God (or, indeed, pure chance), go I".

Caruso noted:

"I could just have easily been born into low scoio-economic status, or homelessness, or born with a mental illness".

Gregg D. Caruso

  • Image by Michelle Maria from Pixabay
  • Image by Herbert Hansen from Pixabay

I know exactly what he means, and agree we should acknowledge our advantages over those less lucky than ourselves, but, strictly, I cannot accept that argument.

I think the argument can only work if one believes (a) in an immaterial soul, which is only housed in the body during mortal life, and could have just as easily journeyed through life in a different body; and (b) even if that soul may impact on the actions of that body in its environment, it is is not changed by those experiences; and (c) that this soul is the true 'I', the identity of the person who refers to themselves as I  (in "I could just have easily been born into…"). Of course, some people may believe just that. But I suspect most people who do believe in some kind of dualism involving something like an eternal soul imagine it is able to (and perhaps even intended to) learn from its incarnation(s).

Who am I?

Even having the debate assumes that one accepts that it makes sense to acknowledge a discrete and relatively stable 'I' (and there are plenty of commentators who feel that this individual self identify soon starts to dissolve when examined too closely). I am happy to acknowledge a kind of distinct and not-overly-plastic 'I', as I think I know what I mean by 'I', and my experiences of that self seems stable and discrete enough to reify it. My self certainly changes, but not so radically and quickly that I awake a stranger to myself (sic) each morning.

But then this 'I' could not just have easily been born into low scoio-economic status, or homelessness, or born with a mental illness.

I was very lucky to be born in a country at peace, in an open society that had a national health service and free education for all; and to loving, caring and supportive parents who were never violent or intoxicated. Money was tight when I was a young child, and the flat where I spent my first few years might not have passed health and safety inspections by today's standards: but we never went hungry, or had to wear torn or dirty clothes; and we slept in proper beds in a secure building; and there was coal for the fire each winter's morning. (For younger readers, coal is a carbon-rich combustible rock which was delivered to homes and used as fuel in open fires in the distant past – releasing filthy dust when handled, and producing choking, polluting smoke when burnt. But, once upon a time, even the rich used it for home heating!) My father always had at least one part-time job alongside his full-time employment to make ends met, but he still always found time to spend with my sister and I when he could be at home. Yes, in the lottery of life, I was very lucky.

Could it have been different?

As I started this post talking about determinism, I should acknowledge that if everything is predetermined, then clearly it could not have been any different! Although I cannot logically refute this possibility I behave as though it has been rejected.

It would seem

a) if I do not have free will then I am only appearing to make choices about what to type (and whether to think I have free will), and even if there was any point worrying about this, whether I do worry about it or not is totally out of my control;

and

b) if I do have free will then I gain nothing by assuming, or acting, as though it is otherwise.

(That is, there is a kind of parallel to Pascal's wager going on here – if you have free will than a bet on anything other than free will looses everything; and if you do not have free will then there is no actual bet to be had, only the illusion of one, and nothing more can be lost).

So, assuming that the course of my life has been the outcome of the choices I have made, and those of my parents, and my friends, and my teachers, and everyone else who's decisions have ever had any influence on my life, then the self I identify with today has been constructed through my experiences of the world, impacted by others, and iteratively built up as I reacted to situations by developing my values and personality; which then influenced (i) my actions and interactions in the world, and so (ii) others' responses to me, and so (iii) the experiences I drew upon in developing that self further…

This is of course just a variation on the constructivist account of learning as incremental, interpretive, and iterative – as we build up our conceptual structures, our mental models of the world, our perspectives, our worldviews, our value systems, our ideologies, our beliefs, our attitudes, our habits, our metacogniti0n, our preferences, our epistemological commitments, and so forth (and these all interact of course) we build up our selves. Indeed, what is the self, if not the gestalt, or perhaps the subsuming system, of these facets of our selves?

Counterfactual 'me'?

So, if my parents had neglected or abused the child who grew to be me then that child would have become someone different to the person I am now, someone else. Even if I had not ended up incarcerated 'at her majesty's pleasure' [sic, a term which reeks of retribution rather than restoration], I very much doubt I would have ever been admitted to a University, or become a teacher, or met my wife (when she decided to do an evening class in physics), or got to teach at Cambridge…

This was Caruso's point, of course, that 'there, but for the grace of God…' – but it would not (by definition) be me who was someone else, as I (the person writing this now) would never have existed. How different that other person would have been is an open question, but I suspect substantially and significantly different.

The sins of the fathers…

But then my parents could not have neglected me or abused me. I do not mean that the people who became my parents could not, under different circumstances, have become very different people and so different kinds of parents – of course that might have been possible. But those hypothetical people are not the parents I  know – they would have been quite different people.

If I had been born in another country… but then no, I could not have been.

Perhaps, under different circumstances, my parents might have emigrated before I was born (not so unlikely as relatives emigrated to Australia and New Zealand when I was young). But my parents, as they developed in their actual circumstances, were not those people, and if the people who became my parents had, under other circumstances, under different life experiences and influences, moved abroad before having children, then again, the self I am would not have developed.

The lottery of making life

Image by Arek Socha from Pixabay
Image by Arek Socha from Pixabay

Indeed, the resulting person might have been very different. After all, I am, not just the result of a social environment, but the unfolding in dialogue with that environment of a biological potential that is genetic. My particular set of genes is not only a unique combination because of the unique genotypes of each of my parents, but is one of myriad potential unique permutations of crossing those two unique genotypes – one particular outcome of the lottery of making life.

If the people who became my parents had emigrated to another country (or even moved to another town) before having children then I would almost certainly not have been born. The number of possible genotypes that could have resulted from crossing my parents (so to speak) is immense. The chances of my genotype becoming the basis of an implanted zygote, and leading to a child, is minuscule (except in the deterministic scenario when it is 1, but I have chosen to (/been predetermined to) disregard that scenario). If my mother had conceived somewhere else – it would not have been me that was conceived.

√
Image by lesia_design from Pixabay

For, without wishing to be insensitive here, if conception had taken place the day before I was actually conceived, or the day after, it would (almost certainly) not have led to the same union of gametes, and the same me.  Indeed, if conception had been delayed a few minutes to make a cup of tea, brush hair for longer, clean teeth… or perhaps had been brought forward by not brushing hair or teeth for as long… then if conception had still occurred (by no means assured) my genotype would almost certainly not have arisen, but would likely have remained one of the vast multitude of possible human genotypes that has never been called upon to guide (or channel, or afford) the biological development of a person.

Given that, you can probably anticipate how I might respond to the hypothetical "had I been born to different parents" – it is a meaningless question. I could not have been born to different parents. We are all very unique. We are also very lucky to be here at all.

Had, say, Henry VIII not fallen out with the Catholic Church, or had Luther's theses blown away, or if Alfred had taken more care over the cakes, I almost certainly would not have been here at all, in the sense that my genotype would likely have never have been expressed (given that it only takes a trivial change in a small domestic detail in the preceding generation to abort or trigger a specific conception, think about the knock-on effects over many generations once one conception is changed), and I certainly would not be here as the person I am today. (And if by some strange fluke of extreme improbability – anything that is not impossible could happen – a baby with 'my' genotype had been born in Victorian England, or even the same time as me but in a Welsh mining village (where they extracted those rocks we all used to burn), then despite some likely similarities, my 'twin' would not be me. After all, even actual 'identical' twins born on the same day in the same place to the same parents are not actually identical (e.g., they develop different fingerprints.)

The veil of ignorance

So the 'there, but for the grace of God, go I' argument does not really make sense to me ,as it should really be 'there, but for the Grace of God, goes someone else' –  which rather lacks the same rhetorical impact.

www.bbc.co.uk

However, I was recently listening to a different programme where Rawls's theory of justice was being discussed, and his notion of the veil of ignorance. The argument here is that people should judge what seems fair on the basis of having no knowledge of their own position in the pertinent social system.

So, perhaps at the end of a science lesson a teacher complains that the practical apparatus and materials have not been properly put away. The teacher offers the class a choice: everyone can miss the start of their break, till everything is cleaned and tided away; or, she will draw lots and select six students to do all the cleaning and tidying, and the rest can go to their break on time. As long as the class decide their preference BEFORE the teacher draws lots, they remain behind the veil of ignorance.

So, in the context of the penal system, the principle suggests that, for example, one needs to decide whether or not it is just and appropriate that someone who has been convicted for the third time of a minor drug offence should be sentenced to many years of imprisonment (at great public expense) before one knows whether one is lucky enough to be brought into the world in a loving, comfortable home, or born to a childhood of poverty and neglect.

Of course, that is, in principle, one should decide from the other side of the veil – we cannot actually regress to that state of ignorance. (Imagine that science teacher first telling the class which six students would be assigned the detention, but then asking the class to chose between the two options without taking that into account!)

In practical terms, this seems little different to Caruso's formulation, as both involve an impossible hypothesis (being born in different circumstances but being the same person; making an intellectual judgment before being born at all!)

Yet I think there is an important difference from the perspective of science education.

Asking someone to  make a judgement on what is just without regard to their particular circumstances, whilst sensible in theory, is surely obviously impossible in practice: we cannot put aside knowledge that is essential to us, so it clearly can only be a kind of thought experiment where people do their best to disregard knowledge that actually frames or permeates every aspect of their thinking.

From my perspective, as outlined above, the same should be true of the "what if you had born born in poverty/to abusive parents/in a totalitarian state, etcetera." formulation as that is equally non-viable, and can only be a hypothetical argument. Yet, I am not sure sure that is so obvious to some people. There is something of a common notion that a person is their genes, or at least their genes determine them. Science suggests otherwise.

Image by klimkin from Pixabay
These two individuals share a lot of genes – but not all their genes! (Image by klimkin from Pixabay)

Whilst it is certainly true that with different genes 'you' will be a different person (and indeed with enough different genes… 'you' may be a carrot – that is, with different genes, there is no you, but someone/thing else), but it is certainly not true that someone with your set of genes will necessarily be the person you are. Your genotype had the potential to support the development of a vast range of different people (albeit that range is still a tiny region of the even more enormous array of possible people the general human genome could give expression to).

Unless, that is, my wager is lost and everything is determined. Then you must be you, but not just because you could not have had a different genotype, but also because that genotype could not have been expressed in a different environment, so the developing person that became you could not have had any different formative experiences either.

Sources cited:

Rutledge, D. (2021, 31 Jan). Free will, retribution and just deserts. The Philosopher's Zone.

Watts, R. (2021, 21st Jan). John Rawls's 'A Theory of Justice'. Arts & Ideas.

Fuels get used-up when we burn them

Keith S. Taber

Sophia was a participant in the Understanding Science Project. Sophia (then in Y7) had been burning materials in science. She had burnt some paraffin in a small burner (a glass burner with a wick). Her understanding of the process was not in terms of a chemical reaction, but at a more 'phenomenological' level:

So what happens to paraffin when it burns then?

It keeps on burning… but you, you can put it out easily as well…. we just blew it out…

I see, but otherwise it just carried on burning, did it? Did it carry on burning for ever, if you don't blow it out?

No, 'cause it would run out.

What would it run out of?

The paraffin.

So where does the paraffin go then?

(There was a pause, of about 4 seconds. Sophia laughs, but does not offer answer.)

And what happens to the level of the paraffin in the burner?

It gets lower and lower.

So why's that, what's happened to it?

'cause you are using all of it up, when it's burning.

So it get all used up does, it – so what happens when it's all used up?

You have to refill it.

So for Sophia the burning of paraffin is not seen in terms of basic chemistry (what happens to the substance paraffin during the process of burning?), but rather she seems to interpret what she has seen in terms of everyday ideas – stuff, such as fuels, get used up – if we use it, we no longer have it.

The final question in this sequence ('what happens when it's all used up') is not treated in scientific terms (e.g., from the perspective of the conservation of matter, there is an issue of where the 'stuff' what was the paraffin has gone), but in practical terms: when we use up the fuel in the burner, we need to refill it to do more burning.

Here, understanding in 'everyday' or 'lifeworld' terms seems to dominate her thinking: the familiar idea that things get used-up obscures the scientific question of what happens to the matter in the fuel. Presumably, her teacher wanted her to focus on the scientific perspective, where burning is combustion, a type of chemical change, but it appears her life-world perspective acted as a grounded learning impediment – an existing way of thinking about a phenomenon that is taken for granted and obscures the scientific perspective.

The everyday way of understanding the world could be called the natural attitude. It seems that for Sophia it is 'just natural' that fuels get used up, and so there is nothing there to explain. Arguably, the work of a science teacher sometimes involves persuading students to seek explanations for things they had considered 'just natural', and so not in need of explanation.

Creating an explanation for the soot from Bunsen flames

Letting the dirt out: Creating an explanation for the soot from Bunsen flames in the absence of appreciation the nature of combustion

Keith S. Taber

Jim was a participant in the Understanding Science Project. Jim, a Y7 student, had been studying burning in science. He had been using Bunsen burners, and had been taught about the different flames (i.e., the safety flame, and the 'roaring' blue flame used for heating), and the use of the valve at the base of the burner to select the frame. Not yet appreciating the nature of burning, he was not aware that the soot obtained when interrupting the safety flame was due to incomplete combustion. Rather he had developed his own interpretation of why using the burner with the hole closed off led to a dirty flame:

What is burning, then?

It usually involves a flame. Erm which can either be yellow, orangey-yellow, or …like a, bluey colour, bluey-purple.

I: Oh, so is that significant, the colour of the flame, does that mean something?

J: Well, the yellow one has a lot of …if you touch it with glass or something, …will go black, but if you use the blue flame, it won't, so if you are heating something, you should use the blue flame.

I: Why do you think it goes black, if you use the orangey-yellow flame?

J: Because with the Bunsen burners, if you are twisting the knob, open, the dirt gets out, and you get the nice clear blue flame, but to get the orange flame, you have to have it closed, don't you, and then that doesn't let the dirt out, so it doesn't kind of, when it gets out of the top it doesn't have time.

I: So what happens if the hole is open?

J: You get, a blue flame.

I: Right, and what happens if the hole is closed?

J: Get a yellow flame.

I: And why does the hole make a difference?

J: I don't know, it probably lets the dirt out, or the air get into it or something.

I: So what dirt is this, that might be let out, do you think. Dirt from where?

J: Maybe the excess gas particles that have already been burnt or something. Don't know.

Presumably no one had told Jim that the hole was to let dirt out of the Bunsen so it did not get into the flame. However the hole was presumably letting something in or out (he later suggests, the hole might let air in – perhaps something the teacher had told the class but which had not been readily recalled?) and there was dirt in the flame when it was closed, which was not there when it was open. Jim interpreted his observations in terms of prior knowledge (of what holes do, and of dirt) to construct an explanatory scheme that made some sense of the effect of closing or opening the air hole. This would seem to have potential to be an associative learning impediment of the 'creative' type.