August Wilhelm von Hofmann : biography
August Wilhelm von Hofmann (8 April 1818 – 5 May 1892) was a German chemist.
The Hofmann voltameter is an apparatus for electrolyzing water, invented by August Wilhelm von Hofmann.von Hofmann, A. W. Introduction to Modern Chemistry: Experimental and Theoretic; Embodying Twelve Lectures Delivered in the Royal College of Chemistry, London. Walton and Maberly, London, 1866.
It consists of three joined upright cylinders, usually glass. The inner cylinder is open at the top to allow addition of water and an ionic compound to improve conductivity, such as a small amount of sulphuric acid. A platinum electrode is placed inside the bottom of each of the two side cylinders, connected to the positive and negative terminals of a source of electricity. When current is run through Hofmann's Voltameter, gaseous oxygen forms at the anode and gaseous hydrogen at the cathode. Each gas displaces water and collects at the top of the two outer tubes.
Hofmann was born at Giessen, Grand Duchy of Hesse. Not intending originally to devote himself to physical science, he first took up the study of law and philology at Göttingen. But he then turned to chemistry, and studied under Justus von Liebig at University of Giessen. When, in 1845, a school of practical chemistry was started in London, under the style of the Royal College of Chemistry, Hofmann, largely through the influence of the Prince Consort, was appointed its first director. It was with some hesitation that he, then a Privatdozent at Bonn, accepted the position, which may well have seemed rather a precarious one; but the difficulty was removed by his appointment as extraordinary professor at Bonn, with leave of absence for two years, so that he could resume his career in Germany if his English proved unsatisfactory. Fortunately the college was more or less successful, owing largely to his enthusiasm and energy, and many of the men who were trained there subsequently made their mark in chemical history. In 1864 he returned to Bonn, and in the succeeding year he was selected to succeed Eilhard Mitscherlich as professor of chemistry and director of the laboratory in Berlin University.
Hofmann’s work covered a wide range of organic chemistry. His first research, carried out in Liebig’s laboratory at Giessen, was on coal tar and his investigation of the organic bases in naphtha established the nature of aniline. This substance he referred to as his first love, and it was a love to which he remained faithful throughout his life. His perception of the analogy between it and ammonia led to his famous work on the amines and ammonium bases and the allied organic phosphorus compounds, while his researches on rosaniline, which he first prepared, formed the first of a series of investigations on coloring matter which only ended with quinoline red in 1887.
The Hofmann rearrangement and Hofmann elimination reaction bear his namesake. Hoffmann isolated sorbic acid from rowanberries’ oil in 1859, a chemical compound that is widely used as a food preservative.
Hofmann also was the first to introduce molecular models into public lectures, around 1860 following the earlier (1855) suggestion by his colleague William Odling that carbon is tetravalent. Hofmann’s colour scheme is still in use by some scientists: carbon = black, hydrogen = white, nitrogen = blue, oxygen = red, chlorine = green, and sulfur = yellow. His models look rather odd nowadays, primarily because Hofmann had them built so that they were, in essence, two-dimensional representations of molecules, and with the carbon atom smaller in size than the hydrogen. (It was Loschmidt in 1861 who probably first appreciated the variations in atomic sizes). After 1874, when van’t Hoff and Le Bel independently suggested organic molecules can be three dimensional, molecular models began to assume their modern appearance.
William Henry Perkin was a student of Hofmann at the Royal College of Chemistry in London, when he discovered the first aniline dye, mauveine.
Hoffman died in 1892 and was buried in Berlin’s Friedhof der Dorotheenstädtischen und Friedrichswerderschen Gemeinden.
He was elected a fellow of the Royal Society in 1851. He was awarded the society’s Royal Medal in 1854 and their Copley Medal in 1875.