Fourth chapter (famous)
2002 summary of the "famous chapter four" of Goethe's 1809 masterpiece Elective Affinities by American literature scholar Susan Gustafson. [5]
In famous publications, chapter four is the core chapter of German polymath Johann Goethe's 1809 novella Elective Affinities, in which the characters Eduard and his friend the Captain explain the scientific concept of “elective affinity” to Eduard's wife Charlotte in terms of descriptions of chemical reaction; also discussing the application of the chemical theory (chemical affinity) in the context of their own reactions. [1]

Famous excerpts
Excerpts from chapter four are frequently quoted. The following, for example, is an opening chapter quote of chapter four as found as the header quote to the introduction section to Korean-born American chemistry historian Mi Gyung Kim’s 2003 book Affinity, That Elusive Dream: [4]

“I can put my meaning together with letters. Suppose an A connected so closely with B that all sorts of means, even violence, have been made use to separate them, without effect. Then suppose a C in exactly the same position with respect to D. Bring the two pairs into contact; A will fling himself on D, C on B, without it being possible to say which had first left its first connection, or made the first move toward the second.”

The following, similarly, is a 2008 synopsis take of chapter four by English-born American philosopher Lydia Goehr: [2]

Wahlverwandtschaft – the natural affinity with which different elements adhere to but also repel one another, as if each were choosing its own particular arrangement. Eduard speaks of chemistry and physics; the Captain, too, of how cohesiveness can be seen in liquids with their tendency to form into round shapes-falling drops of water or little balls of quicksilver or molten lead. At the same time, they all hear descriptions of human relations. Elements and persons: each compelled to spring into activity to form novel and unexpected constellations, a lively movement that disturbs each along the way and of which the ending can’t be predicted in advance.”

Scene of chapter four from the 1996 French-Italian film version of Goethe's Elective Affinities.
Japanese chemical engineer Tominaga Keii quotes a full page from chapter four in his section on the thermodynamics of chemical reactions to his 2004 book Heterogeneous Kinetics. [3]

Overview
In the novella, the central chemical reaction that takes place is a double displacement reaction (double elective affinity), between a married couple Eduard and Charlotte (BA), at the end of their first year of marriage (for each their second marriage), and their two good friends the Captain and Ottilie (CD), respectively.

The first marriages, for both Eduard and Charlotte, are described as having been marriages of financial convenience, essentially arranged marriages. Specifically, when they were younger, Eduard was married off to a rich older women through the workings and insatiable greed of his father; Charlotte, likewise, when her prospects were none the best, was compelled or obliged to marry a wealthy man, who she did not love. In the fourth chapter, the characters detail the world’s first ever verbally-depicted human double displacement chemical reaction.

The chapter begins with description of the affinity map (reaction map) or ‘topographical chart’ as Goethe calls it. On this reaction map, we are told that on it ‘the features of the estate and its surroundings were clearly depicted, on quite a large scale, in pen and in different colors, to which the Captain had give a firm basis by taking trigonometrical measurements’. Next, to explain the reaction, we are told:


‘Provided it does not seem pedantic,’ the Captain said, ‘I think I can briefly sum up in the language of signs. Imagine an A intimately united with a B, so that no force is able to sunder them; imagine a C likewise related to a D; now bring the two couples into contact: A will throw itself at D, C at B, without our being able to say which first deserted its partner, which first embraced the other’s partner.’

 AB + CD \to BD + AC  \,

‘Now then!’ Eduard interposed: ‘until we see all this with our own eyes, let us look on this formula as a metaphor from which we may extract a lesson we can apply immediately to ourselves. You, Charlotte, represent the A, and I represent your B; for in fact I do depend altogether on you and follow you as A follows B. The C is quite obviously the Captain, who for the moment is to some extent drawing me away from you. Now it is only fair that, if you are not to vanish into the limitless air, you must be provided with a D, and this D is unquestionably the charming little lady Ottilie, whose approaching presence you may no longer resist.’

This, of course, is the famous double elective affinity reaction.

See also
Goethe’s human chemistry

References
1. (a) Goethe, Johann. (1809). Elective Affinities (chapter IV, pgs. 24-34). In: Novels and Tales: by Goethe, Elective Affinities; the Sorrows of Werther; German Emigrants; The Good Woman; and A Nouvelette, H.G. Bohn, 1854.
(b) Chapter four (Die Wahlverwandtschaften) (German → English) – Wikipedia.
2. Goehr, Lydia. (2008). Elective Affinities: Musical Essays on the History of Aesthetic Theory (Wahlverwandtschaft, pgs. 1-2). Columbia University Press.
3. Keii, Tominaga. (2004). Heterogeneous Kinetics: Theory of Ziegler-Natta-Kaminsky (ch. 2: Thermodynamics of Chemical Reactions, pgs. 11-20; section: Chemical Affinity in 1806, pgs. 16-17). Springer.
4. Kim, Mi Gyung. (2003). Affinity, That Elusive Dream: a Genealogy of the Chemical Revolution (Goethe quote, pg. 1). The MIT Press.
5. Gustafson, Susan F. (2002). Men Desiring Men: the Poetry of Same-sex Identity and Desire in German Classicism (Chapter 2, Goethe | Section: Elective Affinities or Metaphors of Self and (Same-Sex) Desire, pg. 67-91). Wayne State University Press.

Further reading
● Lynch, Sandra. (2005). Philosophy and Friendship (section: Elective Affinity, pgs. 36-44). Edinburgh University Press.

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