Among the scientists concerned by what they perceive as a tarnishing of their public image, chemists have probably had most to endure. Having lost control of the word organic, they have witnessed a tiresome transmutation in which "chemical" has come to mean "contaminant". In every generation scientists have had to fight their corner and scholarship in the history of science has become increasingly sophisticated in tracing their rhetorical strategies. In his fine biography of Justus von Liebig, William Brock explores the career of one of chemistry's greatest apologists, a key player in the promotion of organic chemistry as a beneficent science essential to medical and agricultural reform.

It is the fate of many 19th-century scientists to be remembered for a single discovery or invention: Bunsen for his burner, Liebig for his condenser. Actually, Liebig did not invent his condenser. His reputation more properly rests on the school of chemical research he established in the 1820s in the small university town of Giessen. Having improved methods of combustion analysis, allowing the carbon content of organic compounds to be determined with precision, he attracted a remarkable array of students from across Europe, many destined to play leading roles in academic institutions and in the expansion of the German chemical and pharmaceutical industries. Tradition has it that Liebig was the first to give chemistry students a practical, laboratory-based training. This, as Brock reminds us, is to overstate the case, given that private mining and pharmaceutical schools were already making such provision.

Nevertheless, from an unheated and disused barracks, by 1840 Liebig's laboratories had grown to become the chemical centre of the world. Liebig's contributions to theoretical chemistry have been well documented. During the 1830s, in a fleeting, almost aberrant, moment of collaboration with his Parisian rival Jean Baptiste Dumas, he expounded a theory of organic radicals, which, despite many modulations, still survives. He also attracted controversy by publishing two books which, in Brock's words, moved chemistry into the marketplace: Agricultural Chemistry (1840) and Animal Chemistry (1842).

In the first book, Liebig exhorted farmers to use mineral fertilisers - that is, artificially manufactured minerals - to boost their crops. This required a new rhetoric which transcended the vulgar disjunction between the natural and artificial (still prevalent today) by presenting the artificial as that which restored the natural. In the second book, Liebig not only sought to win over the doctors to the supremacy of his science but also precipitated an academic argument over the role of "vital forces" in living organisms.

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Brock is an excellent guide to these and many other issues over which Liebig could be extremely quarrelsome. He notes the irony that a younger generation of German materialists, such as Hermann von Helmholtz and Carl Vogt, were almost certainly inspired by Liebig's chemicalising of physiology, while Liebig himself, still retaining the idea of the vital force and displaying an almost British liking for natural theology, became one of their most ardent critics.

The book is particularly illuminating on Liebig's relations with the British. His chemical progeny included some 50 British students and he also projected his star German pupil, August Wilhelm Hofmann, into the inaugural chair at London's Royal College of Chemistry. Liebig visited London on six occasions between 1837 and 1855, sometimes finding a more receptive audience than in Prussia and even campaigning for the recycling of English sewage. Brock bestows the title of "honorary Englishman" on him, but one who eventually turned against the greatest Englishman in the art of scientific diplomacy, Francis Bacon. When his theories of soil fertilisation came under attack in the British press, Liebig ascribed this impertinence to the baleful influence of Bacon, whose naive insistence on inductive methods had created a culture in which the primacy of scientific imagination had been lost. Nor did he pull his punches when complaining that leaders of public opinion in England, and often its MPs, would pontificate about science without knowing any.

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Back in Prussia, a watershed came when he chose to leave Giessen for Munich at the behest of Maximilian II. Liebig owned that he relished the escape from the treadmill of teaching. But, with characteristic penetration, Brock uncovers the political dimensions of a move that led to his appointment as scientific adviser to the Bavarian court - an honour he was destined to lose under Ludwig II, to whom he had once tried to teach chemistry but whose preferences were to be Wagner, Wotan and Valhalla rather than Liebig, Prometheus and the laboratory. The result of 30 years of research, Brock's authoritative study is a splendid advertisement for serious scholarship in the history of science.

John Hedley Brooke is professor of the history of science, University of Lancaster.