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In my school curriculum, and in many standard presentations such as Wikipedia, it is claimed that there are four fundamental states of matter: solids, liquids, gases, and plasmas. How was this list developed?

  1. When did the original conception of matter as being divided into solids, liquids, or gases first arise, and by whom? Did this classification exist already in antiquity, or was it a byproduct of the scientific revolution and the discovery of gases as separate from air?
  2. How, when, and by whom was plasma added to this standard list? I find this especially puzzling since, in discussions among physicists, there seems to be pretty widespread disagreement over whether plasma deserves to be on a similar footing as the first three (for example, because it is not separated by a phase transition from the other states).
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    $\begingroup$ Is the classification into earth, water, air, and fire close enough? Because they do map and they predate accurate records of the thoughts. (We know because other authors quoted the originals.) $\endgroup$
    – Mary
    Commented Dec 25, 2023 at 1:45
  • $\begingroup$ Sounds like you should write an answer! If there is indeed a direct line from the ancient elements to the states of matter, demonstrating that would go a long way towards answering this question. But I'd still have questions, for example about the timeline of this process given that plasma was identified far after solids, liquids, and gases. $\endgroup$
    – Rococo
    Commented Dec 26, 2023 at 21:23
  • $\begingroup$ That would exceed the scope of a normal question $\endgroup$
    – Mary
    Commented Dec 26, 2023 at 22:16
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    $\begingroup$ Related: hsm.stackexchange.com/questions/94/… $\endgroup$
    – Mauricio
    Commented Dec 29, 2023 at 17:56

2 Answers 2

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As @Mary notes in the comments, the ancient idea of "earth, water, air, and fire" maps nicely onto solid, liquid, gas, and plasma, but wasn't until the early 19th century that the idea of three states of matter was well established, and plasma only become commonly referred to as a fourth state of matter in the 1950s.

The distinction between solid and liquid go back to antiquity, but the term "gas" was first used for a compressible fluid by van Helmont and published in 1648 in his posthumous "Ortus medicinae" :

This spirit, hitherto unknown, which can be neither be contained in vessels nor reduced to a visible body, I call by a new name, gas.

The modern concept of a "gas" was, however, really only established by Lavoisier more than a century later in the 1770s. By 1847 the idea of the three states of matter was commonplace enough to be included in introductory chemistry textbooks.

I believe William Crookes in 1880 was the first to argue strongly that there exists a fourth state of matter that we would now call a low density plasma, but he did not have our modern concept of a plasma. ("Plasma" was first used for this ionized state by Langmuir in 1928.) There seems to be a big gap, however, between Crookes and the mid-1950s when references to plasma as a "fourth state of matter" started to appear again, largely by people involved in nuclear fusion research. (See here, for example, for a more recent discussion of plasma and its history.)

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  • $\begingroup$ Thanks for this nice writeup. The Crookes letter is especially a treat. Interestingly, the fourth state of matter that he proposes is really an ultradilute gas such that collisions between particles are rare- not at all like our modern conception of plasma. However, he then proceeds to say that he created something like this with a vacuum tube, which does indeed correspond to a plasma discharge. All this is to say that, from a modern perspective, it seems almost like a coincidence that the example of a fourth state that he proposed would still hold today. $\endgroup$
    – Rococo
    Commented Dec 29, 2023 at 3:53
  • $\begingroup$ I am tempted to speculate that the modern push to classify plasma as a fourth state of matter is to no small degree a product of the public interest in nuclear physics in the post WW2/H-bomb era. The first article in your search: calteches.library.caltech.edu/1857/1/boyd.pdf uses this as a significant point of contact by connecting fusion research to the H-bomb. Curious what the details of this revival were but it seems to be rather obscure. $\endgroup$
    – Rococo
    Commented Dec 29, 2023 at 3:58
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    $\begingroup$ @Rococo You make a good point that Crookes didn't really understand what was happening in (what we now call) a Crookes tube and he didn't have the general concept of a plasma, but he is claimed by plasma physicists as the originator of the "fourth state of matter" idea. I'll tweak my answer. $\endgroup$ Commented Dec 29, 2023 at 15:52
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The terms "solid" and "liquid"/"fluid" seems date back to Proto-Indoeuropean. Early civilizations worked out metallurgy, the use of snow/ice, and rustic methods of distillation.

During antiquity, many civilization introduced a version of the classical elements. In Europe, Empedocles is often cited as the one having introduced the idea of the four elements: earth, water, air and fire. Aristotle would later expand on Empedocles' theory. These classical elements could be seen as an early version of the states of matter but also as an early periodic table.

Note that Aristotle already speaks of some phase transitions. Regarding vapor (Meteorologica):

I have proved by experiment that salt water evaporated forms fresh, and the vapour does not, when it condenses, condense into sea water again.

The next step in the evolution of the "elements" arrived with the development of alchemy during late Greco-Roman civilization and the Islamic Middle Ages. Geber (Jābir ibn Hayyān) classified matter in terms of four properties: hotness, coldness, dryness, and moistness. European alchemist Paracelsus classified matter in the tria prima: salt (solid), mercury (liquid) and sulfur (flammable). However during this period, many other alchemical elements were proposed, see Wikipedia alchemical symbol for various classifications. These elements go more into the classifications that would result later in the elements of the periodic table and not on the states of matter.

Less esoteric classifications reemerged with the development of chemistry. As others have noted, Jan Baptist van Helmont introduced the concept of "gas" in the 17th century (before that these substances were called "airs" or "vapors"). The study of gases would lead to the gas laws, the ideal gas law and eventually to the atomic theory of gases.

The development of thermodynamics would lead to the discovery of the triple point of water by Lord Kelvin in the 19th century. J. Willard Gibbs would introduce the term "phase". The microscopic understanding of matter in the 20th century, would lead to the precise quantitative understanding of phase transitions (by people like Paul Erenfest or Lev Landau). Irving Langmuir would introduce the concept of plasma in 1928.

At what point between the alchemical elements and modern theory did the concept of "solid, liquid, gas" + "plasma" became the norm is hard to assess and merits more research.

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