Gerhardt

Charles Gerhardt (1816-1856) was born in Strasbourg to a bourgeois Jewish family with both German and Alsatian roots. With the prospect of helping his father make a success of a white lead factory in which he had a major financial interest, Gerhardt was sent to the Karlsruhe Technische Hochschule in 1831, then two years later to the Leipzig Gewerbeschule. Here he: lodged and studied with O. L. Erdmann and published his first scientific paper in Erdmann's (and later Kolbe's) Journal für praktische Chemie . During winter semester 1837/38, he studied in Liebig's lab in Giessen, thereby acquiring an influential protector. On Liebig's advice, he then traveled to Paris where he was associated with Dumas and H. Sainte-Claire Deville at

the Faculté des Sciences and the Sorbonne and with A. Cahours at the Jardin des Plantes.

Liebig, who just then was becoming disillusioned with polemics over theory, sought to discourage his protégé's predilections in that direction:

You will destroy your future and irritate everyone, like Laurent and Persoz, if you continue to make theories. . . . The Academy [of Sciences in Paris] has always reserved for itself the right of making laws in science, and it considers anyone else doing this as a thief and an assassin. . . . You always think you are on the neutral soil of Germany, but in fact you are standing on ground which contains all sorts of combustible matter.

Liebig urged Gerhardt to tie himself personally to Dumas, who has "a magnificent character" and likes to take promising young chemists under his wing. "But for the love of God, don't write any more theories except for German journals!"^[8]

Even as a young man, Gerhardt was headstrong, outspoken, and dogmatic, and his relationship with Dumas was from the beginning somewhat uneven. His ardent republican political convictions did not mesh with Dumas' moderate conservatism, and his ties to Liebig created friction in a period when Dumas' relations with the Giessen school were starting to unravel. Moreover, Liebig was correct in perceiving a fundamentally positivistic flavor among the leaders of Parisian chemistry, which conflicted with Gerhardt's visceral theoretical orientation. In 1841, Gerhardt received a provisional appointment at Montpellier, which was made permanent in 1844. In a letter of gratitude to Liebig, Gerhardt attributed both this career triumph and his general success as a chemist to his teacher's influence. But no sooner had Gerhardt arrived in Montpellier than he began to complain bitterly to Liebig of provincial life and the poorly provisioned laboratory facilities.^[9]

In 1842 Gerhardt published one of his greatest papers and simultaneously committed one of his greatest faux pas. He had come to the conclusion that organic chemists needed to unite their formula notation with inorganic conventions by taking all formulas at two volumes instead of the usual four. This would eliminate many dualistic formulas that posited the preexistence of water, ammonia, oxides, and so on in organic acids, bases, and salts, but since the advent of type theories such electrochemical rational formulas were no longer popular in France anyway. In the context of French chemistry of the early 1840s, a very good case could have been made in favor of such ideas. They

were later viewed as constituting the essential step away from a misleading and inconsistent notation to untitled, consistent, and essentially modern formulas. Although Gerhardt did not say so and may not in fact have realized it, his reform proposal was equivalent to accepting the hypotheses of Avogadro.^[10]

Unfortunately, Gerhardt committed two serious errors in this paper. One mistake was a certain degree of conceptual and linguistic confusion. Even when a historian reads this paper with full knowledge of both contemporary and subsequent events in mind, it is sometimes difficult to extract Gerhardt's precise meaning. There were a few egregious lapses: one example is Gerhardt's claim that atoms, volumes, and equivalents are exact synonyms. A second paper on the same subject published the following year solved a few of these problems, but not the most serious ones.^[11]

Even worse for the future of his career, Gerhardt expressed himself in socially inappropriate terms. When his paper was read at the Acadé-mie on 5 September 1842, some members of the audience were shocked to hear what seemed to be arrogant and imperious language from this young man, and they let him know in no uncertain terms. Dumas had wanted to suppress the theoretical part. V. Regnault was furious at some of his formulas being declared "wrong," and Baron L. J. Thenard said the style would not have been appropriate even for a Lavoisier. Later that month back in Montpellier, Gerhardt recounted the disaster in a letter to his friend Cahours. He said he had asked Thenard timidly later that day why he didn't like the paper. "For a moment I thought he was going to eat me," Gerhardt related. He and others agreed, Thenard had said, that the language was "not French" and "not academic" and that the style was infuriatingly imperious (such-and-such a formula is "false," the notation "must be changed," and so on). Thenard concluded by screaming "Adieu, monsieur!" at least ten times before Gerhardt got the hint and excused himself. Liebig received the same news from Gerhardt and replied, "You have Italian blood, too hot for the Parisians." Liebig noted that Gerhardt's fatal error was not to have heeded his warning about avoiding theory in Paris.^[12]

In the fall of 1843 Gerhardt met Laurent, and they quickly became friends and comrades in arms. Gerhardt's judgment of Laurent in his letters to Cahours underwent a reversal from derogation to adulation. Laurent, like Gerhardt, was an uncompromising iconoclast and an ardent republican, cut off from the power structure in Paris and a professor at a provincial faculty, namely, Bordeaux; he may also have been Jewish.^[13] Also like Gerhardt, Laurent was collegially closer to the Giessen circle than to Paris. He had visited Giessen for a time dur-

ing the autumn of 1844 and had quite favorably impressed both Liebig and his assistant August Wilhelm Hofmann (it was under Laurent's influence that Hofmann began to study the halogenation of aniline). His angry confrontations with Dumas over priority matters during the late 1830s, which had alienated his former teacher, could not but have stirred sympathy for him in Liebig's circle.

Laurent was soon converted to Gerhardt's atomic weight reform, and in December 1844 Laurent wrote to Liebig and Hofmann to urge them to accept it as well. Unfortunately, Liebig considered the reform to be nothing more than yet another French theory, and declined; Hofmann was presumably too cautious and too professionally insecure to associate himself with the reformers. "Eh! bien, marchons seuls," Laurent wrote Gerhardt in resignation.^[14]

A more serious problem arose a year later when Gerhardt infuriated Liebig by criticizing as "completely false" his work on a series of complex nitrogen compounds. Liebig promptly published a blistering diatribe entitled "Herr Gerhardt und die organische Chemie, Erste Artikel," openly accusing Gerhardt of the vilest perfidy and calling him a "highwayman."^[15] He also urged Laurent to break off his "monstrous alliance" with Gerhardt. "If you associate yourself with him," Liebig wrote, "it is you who will lose because he has nothing to lose. Read carefully my article, and tell me whether this man has the truth in his soul."^[16] But Laurent refused to abandon his friend and wrote him a kind letter of support and consolation. Laurent related that on his recent visit to Giessen, Liebig had apologized to him for his earlier unjustified attacks and had vowed that his next angry polemic would rest six months in his desk first! He assured Gerhardt not only that Liebig would cool off, but that he would eventually realize that the new atomic weights are correct.^[17]

Gerhardt had criticized Liebig's formulas largely on the basis of the "even-number rule" developed by Laurent from certain regularities in the numbers of hydrogen atoms in organic formulas noted by Gerhardt in his 1842 article. The rule as generalized by Laurent (1845) states that although there may be any number of carbon and oxygen atoms in organic formulas when expressed in Gerhardt's two-volume convention, the sum of all the hydrogen, halogen, and nitrogen atoms must be an even number.^[18] At the time of its formulation, this law was merely an empirical generalization unmotivated by theory, but it seemed to hold for every well-studied organic compound; the only exceptions were cases where there was some reason to suspect analytical inaccuracies, and a handful of contrary instances, such as Liebig's nitrogen compounds. It was little wonder that Liebig was unconvinced by this sort of reasoning.

By this time Laurent had given up his unhappy post in Bordeaux and was living in poverty in Paris. As he and Gerhardt were virtually cut off from the traditional French journals, they had started their own, entitled Comptes rendus des travaux de chimie . This was essentially a review journal modeled on Berzelius' Jahresberichte , as well as an organ for publication of their own papers.

It would seem that at least in one respect Gerhardt had learned his lesson, for after 1842 he pursued a much more openly, indeed often dogmatically, positivist course. Having long denied the preexistence of the dualists' water and oxides in acids and salts, he now denied the real existence of any and all radicals within compounds. In fact, he argued that it was beyond human capabilities to discern any information at all regarding molecular constitutions, and so he began to rely exclusively on empirical molecular formulas. In this he was resisted by his compatriot Laurent, who used constitutional theories habitually and continuously, though professing more a conventionalist than a realist philosophy of science.^[19]

Perversely, this new Gerhardtian positivist-empiricist organic chemistry was rich in new doctrines and ideas, among which were the revised atomic weights and Laurent's even-number rule. The former was an early version of the reform established nearly two decades later at the Karlsruhe Congress of 1860; the latter represented the first seed of what would eventually grow into the theory of atomic valence. Gerhardt also began to develop the concept of homologous series, an idea first broached by Dumas, which would prove extremely productive and heuristically important. These ideas were treated systematically in Gerhardt's first book, Précis de chimie organique (Paris, 1844-1845). Although this work was not well received—not even by Laurent, who subjected it to a searching critique—and although Gerhardt himself described it later as a "horrible old book," it contains the basis of many of his contributions to organic chemistry.^[20]

The way out of the morass was finally perceived by Laurent. In the summer of 1846 he wrote Gerhardt:

I have carefully pondered equivalents. The words equivalents, atoms and volumes cannot be synonymous. . . . There are atoms, there are proportional numbers, but not equivalents. . . . Indeed, the proportional number is a number chosen arbitrarily; one can take it to agree with the atom or volume and to give the simplest notation. The equivalent is different: it is that quantity of a simple body which must be employed to replace another simple body and play its role.^[21]

These thoughts were published that fall in a major theoretical paper that fully clarified Gerhardt's terms arm straightened out the concep-

tual confusion in the 1842 reform proposal. "M. Gerhardt's atom," Laurent stated, "represents the smallest quantity of a simple body which can exist in a compound . My molecule represents the smallest quantity of a simple body which must be employed to produce a combination ; this quantity splits in two in the act of combination." For instance, an oxygen molecule splits into two oxygen atoms to form two molecules of water; a molecule of chlorine splits into two atoms, one of which substitutes for a hydrogen atom of an organic molecule, with the other combining with the hydrogen thus split off to form a molecule of hydrochloric acid.^[22]

In hindsight, Laurent's modification of Gerhardt's reform appears to establish at a stroke the basis for modern chemistry. In fact, it did nothing of the kind. In the late 1840s the Laurent-Gerhardt system was only a schematic proposal with considerable esthetic appeal, but based essentially on thoughtful rationalization rather than empirical verification. Moreover, it was in conflict at many points with well-accepted chemical theory and was still troubled by a number of anomalies. Laurent himself recognized all of these weaknesses and urged Gerhardt not to lose courage.^[23] The theoretical anarchy of this period is well summarized by Laurent's ironic summary description of a course he had been invited to teach at the Sorbonne in the summer of 1847:

Introduction . The entire science is placed in doubt. Atoms are perhaps divisible; dualism is attacked; nomenclature is insufficient; ditto for classifications; all compass bearings are lost, we need a guiding thread. Embarrassment of the professor who teaches a science in which he does not believe.^[24]

Laurent was then suffering both extreme penury and depression. "What misery! What a bitch life is! Not a sous in my pocket!" he cried out to Gerhardt.^[25]

The following year Gerhardt converted Laurent's sarcasm into a book entitled Introduction à l'étude de la chimie par le système unitaire , dedicated to Laurent. It is here where Gerhardt most clearly stated his conviction that molecules must be treated as unitary entities and must be described only by empirical formulas. Reactions of synthesis and analysis say nothing about the constitutions of compounds, for every chemical reaction sets up a violent motion among the atoms in the molecule that totally scrambles their arrangement. Organic chemical theories, he said, must therefore be based on taxonomic rather than constitutional ideas, on reactions rather than structures. In this he was representing a well-established French positivist tradition in chemistry that was fundamentally opposed to many German, English, and Berzelian conceptions.^[26]

This book, reflecting the theoretical anarchy in chemistry, appeared the same month when political anarchy emerged in Paris, the opening wedge of the long sought republican revolution. Understandably, the fortunes of Laurent and Gerhardt suddenly appeared promising again. In March Laurent was named assayer at the national mint, where he fitted up a small laboratory; Gerhardt immediately abandoned his position in Montpellier to join him there. Arago and Quesneville, republicans, and Cahours, a liberal, greeted the revolution warmly; many who had more conservative or centrist convictions were frightened by it. Dumas appeared to change camps, writing a discourse strongly favoring the republic; the apparent hypocrisy scandalized those on the left.^[27]

Gerhardt called on Dumas on 26 March, and described the encounter in a letter to his wife, still residing in Montpellier. Dumas received him coldly and was about to show him the door when Gerhardt suggested that Dumas' conduct "had been unworthy."

At once he became timid as a lamb. So he was afraid. I changed tactics and told him that he had been wrong to abdicate the good position that he had had in science, to turn to politics and administration; that he alone in France was able to understand my ideas (mine and Laurent's) . . . Then Dumas protested of his devotion to science, vigorously denied any hostility to me, and began to weep! Was he sincere at this moment? I have no idea, but I want to believe it. He shook my hand several times and we parted perfectly well. Our conversation had lasted nearly an hour and a half, and surely no one has ever dared to tell Dumas the truth as energetically as I. . . . I am sure now that he will do anything for me to prevent me from denouncing him.^[28]

There were several vacancies in Paris, and Gerhardt and others mounted a vigorous attack on the system of cumul that allowed prominent academics such as Gay-Lussac and Dumas to accumulate almost any number of posts simultaneously. Laurent and Gerhardt both sought to influence the provisional regime's minister of culture Hippolyte Carnot (brother of Sadi) to procure appropriate positions, with promising results. Gerhardt reported to his wife that all of his former enemies were treating him very well now. "If there is justice in the world I will succeed this time; now or never."^[29]

Unfortunately for Gerhardt, Carnot was gone by July, and by the following year the republican tide was waning; all of his hopes began to evaporate. In the spring of 1849 he described himself to his wife as being in a "veritable state of fever," reading ten or a dozen newspapers every day, but lying low for the sake of his family. During the June riots he wrote: "I must tell you, you are making a coward of me! If the

insurrection is vanquished this time, it will be the death of democracy in all of Europe." Vanquished it was.

Gerhardt's enemies, especially Dumas, emerged stronger than ever before. Even more tragic, from working in his cold and damp cellar laboratory at the mint—described by Gerhardt as a "veritable glacier"—Laurent contracted a severe case of tuberculosis in December 1850; he lingered on over two years before finally succumbing. His last days were bitter in the extreme.^[30]

Now essentially unemployed and desperately in need of a protector, Gerhardt wrote Liebig in an attempt to patch over their quarrel:

You know, monsieur, that basically there is no important difference between our theoretical opinions. . . . One could still today define organic chemistry as the chemistry of compound radicals; it is only a question of making very precise the meaning of the word radical, and of removing from it that absolute signification which you yourself have never assumed, and which has been interred with Berzelius.^[31]

Liebig's response, although friendly, was noncommittal. To Hofmann, Liebig expressed suspicions concerning Gerhardt's sincerity and motives. In February 1851, using money lent by Gerhardt's Scots mother-in-law, he and the infirm Laurent began to accept pupils in a private "École de Chimie Pratique," and both began to write definitive treatises of chemistry.^[32]

This was the low point for the reform movement of Gerhardt and Laurent. Its revival was associated with remarkable breakthrough discoveries by Gerhardt and Alexander Williamson and by the work of Wurtz, to whom we now turn.