Hofmann voltameter inventor- August Wilhelm von Hofmann

August Wilhelm von Hofmann – inventor of Hofmann voltameter

August Wilhelm von Hofmann

Biography & Contributions

August Wilhelm von Hofmann was a German chemist born on April 08, 1818 – died on May 05, 1892. Hofmann made considerable contributions to organic chemistry. Hofmann’s received prestigious medals like Royal Medal in the year of 1854, Copley Medal in the year of 1875.

His research on aniline helped lay the basis of the aniline-dye industry. His earliest research on coal tar laid the groundwork for his student Charles Mansfield's practical methods for extracting benzene and toluene and converting them into nitro compounds and amines. Hofmann prepared three ethylamines and tetraethylammonium compounds and established their structural relationship to ammonia. His discoveries include formaldehyde, hydrazobenzene, the isonitriles, and allyl alcohol.

His name is associated with the Hofmann voltameter and with a number of processes which he investigated, including the Hofmann rearrangement, the Hofmann-Martius rearrangement, Hofmann elimination, and the Hofmann-Loffler reaction.

Hofmann also discovered a reaction for deriving amines from amides and developed the Hofmann method of finding the vapor densities, and from these the molecular weights, of liquids.

Hofmann was the first to introduce molecular models into public lectures. In 1863, Hofmann showed that aniline blue is a triphenyl derivative of rosaniline and discovered that different alkyl groups could be introduced into the rosaniline molecule to produce dyes of various purple or violet colours. Hofmann studied nitrogen bases, including the development of methods for separating mixtures of amines and the preparation of large numbers of polyammonias.

He also examined its derivative, allyl isothiocyanate and studied various other isocyanates and isonitriles. Hofmann also developed a method for determining the molecular weights of liquids from vapour densities. Hofmann isolated sorbic acid from rowanberries' oil in 1859, a chemical compound that is widely used as a food preservative.

Hofmann Voltameter

The Hofmann voltameter is an apparatus for electrolyzing water, invented by August Wilhelm von Hofmann in 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. A Hofmann voltameter is often used as a demonstration of stoichiometric principles, as the two-to-one ratio of the volumes of hydrogen and oxygen gas produced by the apparatus illustrates the chemical formula of water, H2O.

Coal Tar

Coal tar is a brown or black liquid of extremely high viscosity. Coal tar is among the by-products when coal is carbonized to make coke or gasified to make coal gas. Coal tars are complex and variable mixtures of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.


Tetraethylammonium is a quaternary ammonium cation consisting of four ethyl groups attached to a central nitrogen atom, and is positively charged. It must exist in association with a counter-ion, and is most commonly found in simple salts such as tetraethylammonium chloride, tetraethylammonium bromide, and tetraethylammonium iodide and tetraethylammonium hydroxide. Tetraethylammonium salts are used in chemical synthesis, have briefly been used in clinical applications, and are widely employed in pharmacological research.

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