In chemistry, Wilhelm Heinrich Sebastian Buchholz (1734-1798) was German physician, chemist, and pharmacist noted for having been an early chemistry mentor or scientific comrade to German polymath Johann Goethe. Buchholz may have been the role model for the Captain in Elective Affinities (see: Geothe's human affinity table).
Buchholz and Goethe were part of a current science society at Weimar called Freitagsgesellschaft (Friday Society), a group that met from 1791 to 1797. The members of the society were charged to present their current research to the others. Buchholz was said to have discussed his latest chemical findings, physician Christoph Wilhelm Hufeland (1762-1836) discussed macrobiotics or the art of prolonging human life, and Goethe was said to have presented his theory of colors.  Buchholz remained an active an honored member of Goethe’s celebrated “Freitaggesellschaft” (Friday Society) up until Buchholz’s passing in 1798. 
It seems that Buchholz was acquainted with Goethe at about the time Goethe was an official member of the government of Weimar, or at least as early as 1783.  The pair worked together on the analysis of water and its purification by the use of powdered charcoal. Goethe’s debt to Buchholz was said to have been considerable, which Goethe supposedly admits in the narrative entitled “Geschichte meines botanischen Studiums” (History of my Botanical Studies) which closes his Metamorphosis of Plants.
Buchholz may have been a role model to the character of the Captain in Goethe’s 1809 Elective Affinities. In his 1916 article “Goethe and the Chemists”, author Roy Temple House describes Buchholz as a “prosperous and jovial man of the world” and “genuine scientist.” This seems to fit the description of the Captain. Buchholz was said to have kept up a large garden which contained not only herbs needed for business, but also rare and newly discovered plants. This is similar to how the Captain worked out a reformulated landscaping of the estate. Buchholz is described as having “kept himself well-informed as to new discoveries and developments in his own and related sciences”.  This is similar to the response of the Captain, in chapter four, when queried by Charlotte about what elective affinities are:
“As well as I can from what I learned from reading about [affinities] some ten years ago. Whether the scientific world still thinks of it in the same way, or whether it agrees with the latest theories, I cannot say.”
As Goethe conceived of and began writing the novella in 1808, the comment of ten year ago would coincide with Buchholz’s death in 1798 and to Buchholz’s presentations of the latest discoveries in chemist at the weekly Friday Society meetings, in the seven years prior.
Buchholz studied medicine and obtained his medical degree, but after leaving school devoted himself to pharmacy and bought the sole apothecary shop in Weimar. He is described, in a caption to an engraved picture of him, as the chief physician of Saxon-Weimar. 
1. House, Roy T. (1916). “Goethe and the Chemists”, Popular Science, pgs. 332-37. Apr.
2. Wilhelm Heinrich Sebastian Buchholz (engraving with caption) – UPenn.edu.
3. Richter, Simon. (2005). The Literature of Weimar Classicism (pg. 323). Boydell & Brewer.