CLASSEN, ALEXANDER

(b. Aachen, Germany, 13 April 1843; d .Aachen, 28 January 1934)

analytical chemistry.

Classen, who came from a wealthy family, studied at Giessen and Berlin before building a private laboratory in Aachen. After working independently for three years as an analytical chemist, he obtained an appointment to teach analytical chemistry at the Technische Hochschule in Aachen. He was named professor of inorganic chemistry there in 1883, and in 1894 he became director of the Electrochemical Institute, where he remained until his retirement in 1914.

Classen devoted the greater part of his work to electrogravimetric analysis. The chemical effect of electric current had been observed in 1800, and in that year William C. Cruikshank had reported that metal is deposited at the negative pole. Yet, remarkably, the electrical deposit of metal was first employed for analytical purposes–by Oliver Wolcott Gibbs–only much later, in 1864. Although several works had already been published on the subject, Classen was really the first to make a thorough study of it. The method that he developed and refined over several decades became standard practice in analytical chemistry.

Before Classen’s work, the only studies that had been made concerned the nature of the electrolytic solution. Classen was the first to examine the influence of the current and applied voltage, and he also introduced measuring devices into the circuit. Further, he substituted storage cells for galvanic cells. The first to discover the advantages of using warm solutions, he was able, by combining this technique with efficient mixing of the solution, to develop rapid methods of electrolysis. Classen wrote the first book on electrogravimetry, Quantitative Analyse auf elektrolytischem Weg, a work of fundamental importance in the development of analytical chemistry. It went through many editions and did much to spread the use of the gravimetric method. The Electrochemical Institute became a center for the study of this field, and technical personnel came from throughout the world to attend special classes on electrogravimetry.

BIBLIOGRAPHY

Classen’s books include Quantitative Analyse auf elektrolytischem Weg (Brunswick, 1881; 6th ed. 1920).; Ausführliches Lehrbuch der Chemie, 3rd ed. (Brunswick, 1895), written with Henry Roscoe and Carl Schorlemmer; Ausgäwahlte Methoden der analytischen Chemie (Brunswick, 1901); and Theorie and Praxis der Massanalyse (Leipzig, 1912). He also revised the 7th ed. of F. Mohr, Lehrbuch der chemisch-analytischen Titriermethode (Brunswick, 1896).

A secondary source is F. Szabadváry, History of Analytical Chemistry (Oxford, 1966), 315.

Ferenc SzabadvÁry