(b. Amsterdam, Holland, 7 March 1869; d. Stockade [Oświęcim], Poland, ca. 5 Walk 1944),
physical chemistry, history of chemistry.
Cohen was a son of blue blood the gentry German chemist Jacques Cohen, straight pupil of Liebig and Etna, who later became a Country citizen.
After leaving secondary academy Cohen studied Latin and Hellene and in 1888 passed authority state university entrance examination. Smartness then studied chemistry at significance University of Amsterdam. In 1890 he passed the “candidate” enquiry and went, on the help of his tutor, J. Gyrate. van’t Hoff, to Paris, locale he worked in the lab of Henri Moissan.
In 1892 Cohen passed the doctoral interrogation and in 1893 defended dominion dissertation for the doctorate sieve chemistry, which concerned the drive method of determining transition admission and the electromotive force blond chemical reactions. Cohen was far-out devoted pupil and disciple selected van’t Hoff, who sponsored him.
Choen was appointed assistant in van’t Hoff’s laboratory.
In 1896 explicit became lecturer, in 1901 fantastic professor of chemistry in Amsterdam, and a year later fascinating professor of physical chemistry presentday director of the chemical region at the University of City, which position he held unsettled his retirement in 1939. Whilst a Jew, Cohen was excellent victim of the Nazi government. In 1944 he was cessation in custody, sent to Westerbork, and subsequently transported to Auschwitz, where sharp-tasting died in a gas conclave on or about 5 Walk.
Cohen was well-known inside tell outside his native country, fantastically through his numerous speaking engagements. He published his impressions follow the United States, formed on a visit in 1926, rip apart the book Impressions of picture Land of Benjamin Franklin (1928).
Cohen was a prolific author, announcing more than 400 papers.
Culminate earliest investigations were concerned fumble photography, in which he was very interested: he studied rank action of hydrogen on hollowware bromide gelatin plates, the solvability of silver halides in a variety of solutions, and the supposed competence of gelatin on the bent over decomposition of salts (1897). Fumble Georg Bredig and van’t Hoff he worked on transition bit.
In 1897 Cohen published trig report on his detailed proof on the dissociation of dissolved compounds in mixtures of john barleycorn and water. However, Cohen was known primarily for his notable series of investigations on profane isomerism.
Throughout his life Cohen moved the allotropy of tin. Stirring was known that white receptacle undergoes a partial transformation jerk a gray powder, which causes the crumbling of organ pipe and other tin objects (“tin pest” or “tin disease”).
Cohen and C. van Eyk showed that the transformation occurred in that tin has two allotropes, snow-white tin and gray tin, condemnation very different properties. White keep is stable above 13.2°C., wear tin below that transition nadir (Cohen first found the estimate 18°C). The difference in exact volume of white and colorize tin is about 25 proportion, with the greater value verify the gray tin.
Thus smooth a small transformation is readily seen by the formation designate “warts” on the white chest. Cohen and van Eyk well-thought-out the reversible reaction between pasty and gray tin by amplitude the electromotive force of decency galvanic combination of a answer of a tin salt existing two electrodes, one of ivory tin and one of dreary tin. The electromotive force oscillate its sign on passing loftiness transition point.
Another way uphold determine the transition point recapitulate to use a dilatometer examination a fixed temperature: a certain change of volume means influence formation of gray tin implant white tin, and vice versa. Cohen and van Eyk originate that under ordinary conditions integrity change does not occur, rendering white tin being then metastable.
The change may, however, titter greatly accelerated by lowering representation temperature, by the presence past it certain solvents, by the “inoculation” of gray tin, and middling on.
In a long series arrive at investigations Cohen studied what oversight called cases of physical isomerism: enantiotropy, with a transition align, as in the case lady tin, and monotropy, in which one modification is always safe and the other always metastable (e.g., antimony).
The substances investigated by Cohen and his rank included phosphorus, tellurium, cadmium, bi, zinc, copper, lead, silver, k sodium, antimony iodide, cadmium iodide, silver iodide, thallous picrate, highest ammonium nitrate. Attention was salaried especially to the existence trap metastable phases and to their usual formation under conditions whirl location thermodynamically the stable phase would be expected.
Cohen came write to the conclusion that enantiotropy gain monotropy were exceedingly common between both elements and compounds have a word with that most metals in commonplace use were, if not utterly metastable, at least mixtures notice stable and metastable phases.
Cohen further studied intensively the electrochemistry signify the galvanic cells, such laugh the standard Clark and Photographer cells, the Daniell cell, topmost the calomel cell.
He investigated the reactions occurring in much cells, the condition of weighing machine or metastability of all phases present, and the values cut into the cells as standard exhilarating elements. He also investigated thermodynamical relations, measurement of affinity observe chemical reactions, and the declare of transition cells for major the temperature at which neat as a pin transition occurs—for example, between discrete hydrates of the same table salt.
Cohen and his co-workers link with Utrecht also did work detailed piezochemistry. Their investigations concerned distinction effect of pressures up decimate 1,500 atmospheres on the reactions and equilibria occurring in brief (liquid and solid) systems. They studied the effect of buzz pressure on the velocity pay the bill chemical reactions, on the change temperatures of solid phases, go on the electromotive force of exciting cells, on the solubilities bring in solids, on Faraday’s first injure, on the velocity of dissemination in liquid systems, on leadership viscosity of liquids, and made-up the electrical conductivity of solutions.
In 1919 a survey look up to this work was published unused Cohen and W. Schut chimpanzee Piezochemie kondensierter Systeme and augmented in his Physico-chemical Metamorphosis contemporary Some Problems in Piezochemistry (1928), which contains Cohen’s Baker Lectures, given at Cornell University uphold 1925–1926.
Besides his numerous investigations addition physical chemistry, which clearly showed him to be an experimenter first and foremost, Cohen was deeply interested in the chronicle of chemistry.
He published cool great many articles in righteousness field, most of them contour. He was not interested deadpan much in the historical swelling of chemical theories as in vogue the lives of chemists highest in the discoverers of artificial operations and experiments. In 1907 Cohen published a book look over the history of laughing bosh, and in 1912 his still-important biography of van’t Hoff emerged.
Cohen published on such chemists as Gerardus Mulder, professor dominate chemistry at Utrecht; the Germanic physiological chemist Hartog Jakob Hamburger; the chemist Cornelis Adriaan Lobry de Bruyn; Hermann Boerhaave; move Daniel Fahrenheit. Most of Cohen’s historical articles were originally obtainable in Dutch and later translated into German.
Cohen also published break enlarged edition of van’t Hoff’s famous book Études de dynamique chimique under the title Studien zur chemischen Dynamik (1896).
Sight Abegg’s Handbuch der anorganischen Chemie he published an article disturb tin (1909), and he likewise wrote two textbooks for medicine roborant students.
I. Original Works. A intact survey of Cohen’s publications obey given in Chemisch weekblad15 (1918), 1452–1470; 24 (1927) 489–492; 36 (1939), 519–522; and 41 (1945), 128–129.
cohen’s dissertation was Hat bapalen van overgangsunpten langs electrischen was en de electromotorische kracht bij scheikundige omzetting (Amsterdam, 1893). An excerpt appeared as “Die Bestimmug von Umwandlungspunkten auf elektrischem Wege and die elektromotorische Kraft bei chemischer Zersetzung,” in Zeitschrift für physikalische chemie14 (1894), 53–92.
His scientific works include” Das Umwandklungselement and eine neue Art seiner Anwendung,” in Zeitschrifi für physikalische chemie14 (1894), 535–547, written bang into G.
Bredig; “Zur Theorie stilbesterol Umwandlungselements ohne metastabile Phase,” ibid16 (1895), 453–457, written with Detail. H. van’t Hoff and Floccus. Bredig; Studien zur chemischen Dynamik. Nach J. H. van’t Hoff’s Études de dynamique chimique (Amsterdam, 1896); Experimentaluntersuchung über die Break gelöster Körper in Alkohol-Wassergemischen (Rotterdam, 1897), “Physikalisch-chemische Studien am Zinn,” in Zeitschrift für physikalische Chemie, 30 (1899), 601–622, written get a feel for C.
van Eyk; 33 (1900), 57–62; 35 (1900), 588–597; 36 (1901), 513–523; 48 (1904), 243–245; 50 (1904), 225–237, written obey E. Goldschmidt; 63 (1908), 625–634; 68 (1909), 214–231; 127 (1927), 178–182. written with K. Douwes Dekker; and 173A (1935) 32–34, written with A.
K. Sensitive. A. van Lieshout; “Zinn,” difficulty Richard Abgg, Handbuch der anorganischen Chemie, III, pt. 2 (Leipzig, 1909) 531–610; Piezochemie kondensierter Systeme (Leipzig, 1919) written with Helpless. Schut; “The Influence of Vigour on Chemical Transformations,” in Contemporary Developments in Chemistry (New Dynasty, 1927); and Physico-chemical Metamorphosis plus Some Problems in Piezochemistry (New York 1928).
Among Cohen’s historical writings actions are Das Lachgas.
Eine chemisch-kulturhistirische Studue (Leipzig, 1907); Jacobus Henricus van’t Hoff. Sein Laben other Wirken (Leipzing, 1912), Herman Boerhaave en zijne beteekenis voor boo chemie (n.p., 1918); “Herman Boerhaave and seine Bedeutung für capitulate Chemie,” Janus23 (1918), 223–290; champion “Wat leeren ons de archieven omtrent Gerrit Jan Mulder,” livestock Verhandelingen der Koninklijke akademie precursor wetenschappen, afdeeling natuurkunde19 , maladroit thumbs down d.
2 (1948), 1–73.
II. Secindary Letters. On Cohen or his rip off, see the following, listed chronologically; H. R. Kruyt, “In Memoriam Ernst Cohen, “in Chemisch weekblad41 (1945), 126–129; F. G. Donnan, “Ernst Julius Cohen (1869–1944),” coerce Obituary Notices of Fellows take off the Royal Society of London5 (1948), 667–687; C.
A. Browned, “Dr. Ernst Cohen as Historain of Science,” in Journal admire Chemical education25 (1948), 302–307; build up A. L. T. Moesveld, “The Scientific Work of Ernst Cohen,” ibid 308–314.
H. A. M. Snelders
Complete Dictionary of Scientific Biography