Pique the Geek 20090726, Phlogiston, the “Perfect” Theory of Combustion in the 18th Century

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Back in the days when energy was not understood, but after the Aristotelian ideas of the elements were being shot down, folks became interested with why fire “works”.  That is not in the least odd, since fire has been simultaneously our best friend and our worst enemy.

Without fire, food would be rather indigestible, especially meats and starchy things.  With the heat from fire, those become much better sources of digestible nutrition.  With fire, our living structures become comfortable, and without it chillingly cold and very harsh.

But fire has its own way of doing things.  Uncontrolled, it is one of most destructive natural, or human created, forces.  But it is NOT an element.  Neither is Earth, Air, nor Water.

First, some housekeeping.  I still have not bought cigarettes since March but still an using Prince Albert and Top cigarette leaves.  I am slowly tapering off of them, but times like writing essays and responding to comments seem to cause me to increase my intake.  It is because I am sitting in one spot and thus it is convenient to smoke.

Second, take a look at my Tiger Lilies.  These are from stock taken from my grandmum’s yard nearly fifty years ago.  These are “multiplier” plants, in that little bulblets form where the leaves join the stem.  Look carefully on the larger picture below the blooms, about three or four bricks down.  You can see a bulblet (a little round, brownish object) at the joint between stem and leaves.

Now, back to phlogiston.  First, I need to point out that a single student knows more chemistry after ninth grade physical science than the entirety of learned people in the 18th Century.  What they did know empirically was interpreted heavily relying upon Aristotelian philosophy, thus rendering it impossible to formulate realistic theories.

I have very little sympathy for Aristotle, at least his contributions to science.  All that he did was theorize (speculate is more like it) as to how things worked, and if his logical model was OK, his explanation was OK, even when (as was the case more often than not) his basic premeses for his logical development were false.  That individual did more to set back science that almost anyone in memory.  He NEVER did an experiment.  I think, too, but I do not believe that just because that I think something makes is so.  He did.  

The bastion of modern thought (I am being very, very sarcastic), the Catholic Church, took his “wisdom” to heart.  So the center of the universe was the Earth, and so forth.  Just nonsense.  I am continually amazed that the early Christians would take the words of a pagan so seriously.  But I digress.

By the 18th century C.E., folks had sort of given up on Earth. Air, Fire, and Water as the fundamental elements of reality.  The alchemists had done some research (they were off base, but one of them discovered phosphorus, Brand in 1669), and a new way of thinking was just beginning to bloom.  That new method was termed “Natural Philosophy”, “Alchemy”, and, finally, Science.  At least the alchemists performed experimental work.

There was a huge overlap.  Issac Newton, the father of modern mathematics (he took an 18 month break from his duties at the University to invent the calculus) was also an alchemist.  He also claimed to be a virgin from womb to tomb.  Sad for him, in my opinion.

The accepted theory of fire was the phlogiston theory.  In that theory, when a material burned, it gave up phlogiston to the air, thus losing mass.  Metals were combinations of what at the time was called a calx, (we call them the oxide of the metal now) and phlogiston.  Charcoal was rich in phlogiston, so when calx and charcoal were heated together, the charcoal gave up its phlogiston to the calx, thus forming the metal.  This is logical, but incorrect.

Likewise, when wood, coal, or charcoal is burnt, it gives up phlogiston to the air, forming an ash that weighs less than the starting materials, the difference in weight being the amount of phlogiston lost.  Once again, this makes sense, even though it is wrong.

Now, no one ever made an attempt to reconcile that a metal, supposedly a compound of the calx and phlogiston, weighed less than the calx did to begin with.  This fact was conveniently ignored.  This is crucial to understanding the young Earth creationists (aka Intelligent Design adherents) at present.

UPDATE:  Kossack retrograde has corrected me in that I made a mistake by lumping in the Young Earthers with the ID folks.  They are not necessarily in the same philosophical school.  I think that both schools are incorrect, but in the interest of accuracy, I stand corrected, and appreciate the criticism.

When one already has the working model (theory) accepted as immutable “fact”, then the annoying little real facts that do not fit with the preconceived notion are either ignored or explained away.  For example, some of the ID folks really believe that the fossil record was planted all over the planet by Satan to confound mankind, or that radioactive dating techniques are flawed because, darn it, uranium-238 has not always had a half life of 4.5 thousands of millions of years.  Likewise with carbon-14 dating:  the darned cosmic ray flux that converts nitrogen-14 to carbon-14 was very different a few thousands of years ago, or that the nitrogen concentration in the atmosphere was different then, despite all evidence pointing to the contrary in each case.

Things began to get interesting in the middle of the 18th century.  An English cat by the name of Joseph Priestly started fooling around with scientific things (he was acquainted with Benjamin Franklin, by the way) including electricity and gases.  Priestly actually wrote a 700 page book about electricity in 1767, so he was no slouch.  His experiments on air were the important contributions to the scientific method of chemistry.  Priestly had a very large burning glass (a very large convex lens, like a great magnifying glass) that could focus sunlight in a small area.  He focused light on what is now known as red mercuric oxide and found that metallic mercury and an air (all gases were called airs then) that was different than ordinary air.  For one thing, burning objects placed in this air burnt much more vigorously, and a mouse in a container of this air would live much longer before suffocation than a similar one in a container of ordinary air.  Since he believed in the phlogiston theory, he called his new air dephlogisticated air on the theory that it contained less phlogiston than ordinary air, since things burned faster in it, since it was easier for the phlogiston to get out of the burning material since there was less resistance than in normal air.

Just as an aside, Priestly also is the great grandfather of Coca-Cola.  He lived by a brewery, and so has access to large amounts of what we now know to be carbon dioxide.  He collected a good deal of it and shook cold water with it, inventing carbonated water.  Priestly finally got into trouble in England for several reasons, one of which was being a Universalist and another for supporting the French Revolution.  Ironically, the French Revolution would go on to kill the guy who finally formulated the modern theory of combustion.  More on him later.  Priestly and his family ended up in the United States in 1794.  He died in 1804, never rejecting the phlogiston theory, but he did allow that future observations might cause it to be rejected.

Around the same time, another Englishman, Henry Cavendish, discovered that a new air was obtained when metals were exposed to dilute acids.  (Several others had made that observation before, but Cavendish experimented further).  He started playing around with it and found that it would burn fiercely in normal or in dephlogisticated air.  He called this material inflammable air.  We now know it by the name hydrogen.  Cavendish was probably the first to discover that when inflammable air and dephlogisticated air were burned together, pure water was the only observable product.

Now, these folks were pretty logical.  If what we know as oxygen is dephlogisticated air, then there must be something else.  That would be, sure enough, phlogisticated air, what we now know as nitrogen.  Cavendish performed a series of experiments that determined that the atmosphere was 1/5 dephlogisticated air and 4/5 phlogisticated air, remarkably close to the 21% oxygen 78% nitrogen accepted today.  He also did another experiment, using electrical sparks, to remove both of those airs from normal air.  He finally was left with a little bitty bit of gas that would not go away, amounting to just a little less than 1%.  We know today that this was composed of the inert gases, mostly argon, with some neon, xenon, and krypton.  Not bad for 1785!

However, even brilliant experimenters need sound theory, and Cavendish was a phlogistonist.  He reckoned that his inflammable air was as close to pure phlogiston that could be had.  Sorry, Chief, missed it by THIS much.

There was a Frenchman named Antoine Laurent Lavoisier who finally put all of the seemingly disparate facts together, but he had to reject phlogiston to make sense of the observations.  He was an interesting person.  His parents were wealthy, and actually made it to the aristocracy during after he was born.  This actually was not a good thing for him, as it turned out later.  Lavoisier was a very careful and meticulous experimenter, and also had the knack of designing good experiments.  But his greatest ability was the ability to ignore the conventional wisdom and form his own explanations for what he observed.

He began by burning different substances in air and in oxygen and also read the works of Priestly, Cavendish, and others.  He began to piece together that phlogiston just did not make sense.  He put the nail in the coffin when he heated metals in sealed glass containers containing air for form calxes.  Before and after heating, there was no change in mass.  When the seals were broken, he could hear air rushing into the containers, and sure enough, when they were weighed again, they were heavier than before.  That absolutely meant that either phlogiston had a negative mass or that there was no such of a thing.  He did not like the negative mass idea, and to me it is sort of akin to variations in the decay rate of uranium, not consistent with any documented observation anywhere else.

He also burned sulfur, phosphorous, and other materials and found that in every case the products of combustion, when all of them were collected, ALWAYS weighed more that the material being burnt.  Then he burnt dephlogisticated air with inflammable air in closed containers, again with no change in mass.  The conventional wisdom was that phlogiston was “small” enough to escape, and this was found not to be the case.  Also, in every case the only product was pure water.  On went the lightbulb (well, those had not been invented yet).  Lavoisier correctly concluded that combustion was what we now call a chemical reaction between whatever fuel (hydrogen, carbon, etc.) and the dephlogisticated air.  Well, since he had just disproved the phlogiston theory, he needed a better name for that material, and named it oxygen (of rather the French word for it), meaning “acid former” because of the mistaken view that all acids had oxygen in them, or so goes the oft repeated phrase.  However, this is not quite true.

In those days all acids were handled in aqueous solution.  One modern definition of an acid is that an acid is a proton donor.  Well, in aqueous solution bare protons do not exist, but rather are hydrated by water molecules.  Thus, all known forms of acids AT THE TIME did indeed contain oxygen, so Lavoisier is vindicated with the choice of name.  Oh, as a footnote, remember when I mentioned that Priestly was a supporter of the French Revolution and that there was an irony?  In 1794 the guillotine separated Lavoisier’s head from his body, since he was an aristocrat.  He was almost 51 years old.

Lavoisier is rightly considered the founder of the modern science of chemistry, just as Newton is for physics.  He literally wrote the book that served as the standard text for decades and founded the first successful professional journal devoted solely to chemistry.  Distinguished Professor Paul Kuroda from the University of Arkansas used (he is deceased now) to give each of his new Ph.D. graduates a plaque that traced their lineage all the way back to Lavoisier, called “Lavoisier and Me”.  Quite a gesture.  By the way, I go back to the Swedish chemist Berzelius, so no direct connection on my part.

What are we to take away from this?  I think that there are several things.  The most important is that the scientific method, applied correctly, always gives the right answer in systems to which it applies, given enough time.  Theories are not laws.  Laws are concepts so basic and so tested that no exception has ever been found.  For example, the Law of Gravity is a law.  It always works.  Now, there are different explanations for why that is so, one of them being Newton’s theory of gravity.  In its day, it explained everything observed about gravity.  However, as measurements became more accurate, some very minor discrepancies were observed.  It took Einstein’s General Theory of Relativity to remove those discrepancies.  However, it is still a theory even though no exception has yet been found.

One can never “prove” a theory.  All that one can do is either disprove it with new facts, or report that new experiments are still consistent with the theory.  The ID folks rave about Darwinian evolution being “just a theory”, and it is.  But in scientific circles, the word theory has a much more limited and specific meaning than it has in casual conversation.  When I say that I have a theory about how something happened, I really have a hypothesis, which is a best guess that needs independent confirmation, where in science a theory is a concept that has been supported and not refuted by hundreds if not thousands of separate studies.

Another thing to take from this is that it is easy for dogma, either religious or scientific, to cloud judgment.  Folks knew that the calx weighed more than the metal, but they ignored it until Lavoisier forced them to accept that simple fact.  The ID folks are so sure of their dogma that the fossil record is irrelevant, and every observation about radioactive decay to date is just of no consequence.

Finally, the wonder of the scientific method is that it self correcting.  As I said before, given enough time and observations, it will always give the right answer, consistent with the universe of data available.  But when even a single exception is found (and, of course independently verified), the model (theory) has to be changed.  Sometimes such a change can be relatively minor, such as when the “plum pudding” model of the atom was replaced with the more accurate but still not completely correct “solar system” model because of the work by Rutherford.  There were still atoms, just our understanding of them was improved.  Sometimes the change is radical, as with the complete debunking of phlogiston.  But the scientific method always works for systems amenable to scientific analysis, IF people have minds open enough to accept facts rather than preconceived notions.

Well, you have done it again.  You have wasted another perfectly good batch of electrons reading this drivel.  And although Keith Olbermann gets another candidate for the Worst Persons list when he reads me say it, I always learn more than I ever could hope to teach in writing these posts, so keep the comments, questions, corrections, and other technical topics coming.  Remember, there is not any scientific or technical issue that is off topic here.

Next week we will try to finish up Drugs of Abuse with a discussion of the influence that LSD had had on society and the arts.  There is so much material that I have been having a hard time culling through it.

UPDATE:  Thanks to all who recommended this essay.  I very much appreciate it.

UPDATE the Second:  Thanks, budhy, for the front page.  I very much appreciate it.  You know that I am not a “hit and run” essayist, and will stay on for a long while to respond to comments.  This sort of keeps me going, since some life situations are not very happy at present.  This is a healthy diversion for me, and hopefully educational for everyone here.  I ALWAYS encourage comments.

Warmest regards,


Crossposted at Dailykos.com


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  1. Warmest regards,


  2. Science ponderances for today.

    Are cheap energy devices globally suppressed?

    Has NASA suppressed the extra-terrestrial question?

    What is the purpose of the suppression of science information which has been ongoing for the past five or more years?  The “changes” software and otherwise of access to patents.  That most retarded and evil focus on intellectual property promoted via Sarbanes-Oxley.

    The exodus of meaningful trade shows and seminars to third world countries.

    Today’s non-support of science in general.

  3. …that newton’s…situation…actually made him more able to invent calculus in just 18 months, much as george costanza became smarter after becoming master of his own domain?

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