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Image and Reality: Kekulé, Kopp, and the Scientific Imagination, Rocke
For a more detailed explanation of these developments, see QR. To put it plainly, Gerhardt did not view the constitution of sulfuric acid in a different way from Williamson; rather, his formula intentionally avoided advocating any constitutional idea. In the spring of he succeeded in synthesizing the acetic acid anhydride that Williamson had predicted in his Ipswich paper—a symmetrical doubled version of acetic acid with loss of water, the perfect analogue to the doubling of alcohol with loss of water to form ether.
Gehahrdt then took the next Williamsonian step. He succeeded in synthesizing novel asymmetric versions—mixed anhydrides between acetic, benzoic, salicylic, and other organic acids. Hofmann and Kolbe were exact contemporaries, arrived in London the same month October , and became fast friends. But in the fall of Hofmann found that some reactions simply could not be represented this way. He concluded that aniline could not be C12H4,NH3, but rather must be C12H5,NH2; that is, aniline was not a copulated ammonia, but a substituted ammonia.
Hofmann had thus entered the type-theoretical world of the French chemists. He discovered that he had tapped a rich vein. Even before the end of that year Hofmann revealed his creation of an astonishing array of new organic-substituted ammonias, his so-called secondary and tertiary amines—i. Why would removing a single hydrogen atom produce such a dramatic change in physical properties?
Kekulé, Kopp, and the Scientific Imagination
The data on boiling points was supplied by Hermann Kopp. If one could make an asymmetric hydrocarbon by stitching together two different radicals, then one could prove the dimer formulas correct, exactly as Williamson had just done with the ethers. But he could not get the reaction to work well.
But Hofmann had not been successful either. If the maximum capacity is reached, then only substitution, not addition, of other components can occur. Frankland had turned: he now allied himself with the ammonia type theory of Hofmann and Wurtz, for the semimetals antimony and arsenic seemed to follow exactly the pattern established by the new organic nitrogen compounds of the latter chemists.
The theory of copulas, he declared, could no longer be maintained. Both claims have legitimately been interpreted as early approaches to what came to be known as the theory of atomic valence. These new developments worried Kolbe. After much effort, in the fall of Kolbe devised an experimental argument that, he thought, decisively refuted the Williamson- Gerhardt theory, using their own argument turned back upon them.
There is a parallel here to the problems that Galileo had faced more than two centuries earlier.
Image and Reality : Kekule, Kopp, and the Scientific Imagination
To understand the Copernican system, one needed a healthy dose of visual imagination, for it was necessary to think of oneself as standing on a spinning and hurtling globe called the Earth, and to imagine vicariously the other motions of the planets, and all the resulting apparent phenomena as seen from the earth. For details, see QR, — Hofmann arrived there in , Kolbe spent from to there, Frankland spent most of the period from to in or near London, Williamson joined Graham at UCL in , and others, such as John Stenhouse, Benjamin Brodie, Jr.
Most of these men had been associated with Liebig at some point. Dickens, Sketches by Boz Penguin edition, , We will also provide a preliminary assessment of his famous autobiographical tale of a striking vision he later claimed to have had while dozing aboard a horse-drawn London omnibus, which he said led him from valence theory to the much more consequential theory of chemical structure.
He enjoyed a comfortable bourgeois childhood in Darmstadt, the capital of the Grand Duchy, where Liebig had also grown up. During his six years in the Grand-Ducal Gymnasium he won particular praise in science, mathematics, and languages. In drawing and painting he had considerable enthusiasm and talent; every Sunday he took lessons in the studio of an engraver, and some of his early artistic efforts survive. From an early age he also developed his powers of memory to an extraordinary degree, a faculty and habit that stayed with him to old age.
When August showed artistic and mathematical gifts, Emil determined that his son should study architecture for a profession. He obtained small architectural commissions for his son; thus it happened that even as a teenager August drew up the plans for several houses in town. Unfortunately, Emil died shortly before August graduated from the Gymnasium. Without a breadwinner, the family was no longer prosperous, and August needed to choose a profession with pecuniary promise.
As his father had wanted, he enrolled as a student of architecture and pursued the subject conscientiously for two semesters. Upon inquiry, it was learned that there were only three civil-service chemistry jobs in the entire state of Hesse-Darmstadt—the professors of chemistry at the University of Giessen and at the Darmstadt School of Trades,8 and the master of the mint.
He heard lectures by the well-known professor of chemistry Friedrich Moldenhauer, and took a Praktikum in chemical analysis. In his leisure time he continued to exercise his artistic and craft skills, learning modeling in clay, as well as woodcarving and woodturning. He also became a superior glassblower, able to fabricate the complicated Liebig potash-bulb apparatus in a few minutes. For 6. One entire night spent over my books was nothing; only if I did this two or three nights in a row did I think I had earned some merit. It was then that Frankland isolated the purported radicals methyl, ethyl, and amyl, to which event Liebig responded privately to A.
In any case, this testimony suggests that even as early as the late s the younger faculty in Giessen were more open to the reform movement than Liebig was. He formed particularly close personal relations with Wurtz and with Charles Gerhardt, with whom he regularly consorted but not with Auguste Laurent, who was very ill. But Liebig only proposed him for two possible postdoctoral assignments. To the surprise of family and friends he accepted the less likely of the two, an assistantship with an independently wealthy private chemist, Adolf von Planta, in Chur, Switzerland.
This gave him the opportunity, as he later described it, to spend fourteen months honing his organic-analytical skills, while also pondering, in the beautiful Alps, all that he had learned in Paris.
He became personally close to Planta. Liebig proposed him for an assistantship with his former student John Stenhouse, at St. Mein Schicksal wollte das nicht! Whereas previously we had considered questions from two sides, now we examined them even more thoroughly from a third side. Here is how he reasoned.
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One might accomplish this, he thought, using a sulfur analog of the known chlorinating reagent phosphorus pentachloride. There was, of course, no way to hide the powerful aromas of sulfur compounds, but Stenhouse let the work continue. Williamson attended, and answered the paper orally. His rebuttal was detailed, substantive, and rhetorically brilliant—even humorous, often employing a light but incisive hand with an undercurrent of ridicule. That was an excellent education, which made the mind independent. Unsure whether he should even try for the position, he wrote to Planta of his pessimism.
Image and Reality. Kekulé, Kopp, and the Scientific Imagination. Von Alan J. Rocke.
He was nearly resigned, he said, to the very unpalatable idea of going into the industrial job market, as he had considered doing off and on since He did decide to apply for the Zurich professorship, and toward that purpose garnered glowing letters from Williamson excerpted above , Bunsen, Gerhardt, and A. But the one letter he most needed he did not get: he wrote three increasingly anxious letters to Liebig, without receiving any reply. See, e. September But we do know that this was a fast-moving time for chemical theory.
But these developments were complex. In this section we review some of these developments in order to understand more clearly why various leading chemists chose the formulas they did, what they actually meant by some of their words and formulas, and why all of this happened at such a furious cadence.