VAN’T HOFF, JACOBUS HENRICUS

(b. Rotterdam, Netherlands, 30 August 1852; d. Steglitz [now Berlin],Germany, I March 1911)

Physical chemistry.

Van’t Hoff was the third of seven children born to Jacobus Henricus van’t Hoff, a physician, and Alida Jacoba Kolff. In 1867, at the age of fifteen, he completed his elementary schooling and entered the fourth class of the five-year secondary school in Rotterdam. In 1869 he passed the final examination and told his parents that he wished to study chemistry. It was agreed that he would study technology at Delft before going to a university. He completed the usual three–year program at the Polytechnic School at Delft in two years; his teachers there included the chemist A. C. Oudemans and the physicist H. G. van de Sande Bakhuyzen.

At Delft, van’t Hoff also studied calculus and became interested in philosophy. He immersed himself in Comte’s Course de philosophie positive, Whewell’s History of the Inductive Sciences, and Hippolyte Taine’s De L’intelligence. He also read Byron’s poetic works with great fervor.

In 1871 van’t Hoff entered the University of Leiden, where he studied mainly mathematics. From the autumn of 1872 to the following spring he worked with Kekulé at Bonn. In 1873 he passed the doctoral examination in chemistry at the University of Utrecht and early the following year went to Paris for further study under Wurtz. Here he met Le Bel, who later independently published a theory to explain optical isomerism based on stereochemical considerations.

In the summer of 1874 van’t Hoff returned to the Netherlands and in September of that year published his theory of the asymmetric carbon atom, a work that inspired the development of stereochemistry. On 22 December 1874 he obtained the Ph.D.at Utrecht under Eduard Mulder’s guidance for an undistinguished dissertation on cyanoacetic and malonic acids. In 1876 he was appointed lecture in physics at the State Veterinary School in Utrecht and began writing his first book, Ansichten über die organische Chemie (1878–1881).

In 1877 van’t Hoff was appointed lecturer in the oretical and physical chemistry at the University of Amsterdam, where, from 1878 until 1896, he was successively professor of chemistry, mineralogy, and geology and head of the department of chemistry. His appointment was undoubtedly due to J.W.Gunning, professor of chemistry and pharmacy at Amsterdam, who became his lifelong friend. In his inaugural lecture on 11 October 1878 van’t Hoff defended the view that in studying the natural sciences both observation and imagination are necessary. Having studied the lives of many scientists, he concluded that the most prominent among them had been gifted with a highly developed imagination.

After 1877 van’t Hoff began his studies in chemical thermodynamics and affinity, and in 1884 he stated his principle of mobile equilibrium. From 1885 to 1890 he published the results of his studies on osmotic pressure and explored the analogy between dilute solutions and gases. In 1887 van’t Hoff was named professor at the University of Leipzig. Although this invitation catalyzed the authorities at Amsterdam to provide funds for a new chemical laboratory, which was completed in 1891, van’t Hoff moved to Berlin in 1896, having been elected to the Royal Prussian Academy of Sciences and appointed professor at the university. Because he lectured only once a week, he was now able to devote himself completely to research.. His lectures appeared in Vorlesungen über theoretische und physikalische Chemie (1898–1900), which was translated into many languages, and in Die chemischen Grundlehren nach Menge, Mass und Zeit (1912). With Wilhelm Ostwald, he was a cofounder of the Zeitschrift für physikalische chemie, the first issue of which appeared in February 1887.

In 1885 van’t Hoff was elected a member of the Royal Netherlands Academy of Sciences. He received honorary doctorates from Harvard and Yale (1901), Victoria University of Manchester (1903), and the University of Heidelberg (1908); and was awarded the Davy Medal of the Royal Society of London (1893) and the Helmholtz Medal of the Prussian Academy of Sciences (1911). In 1901 he became the first Nobel laureate in chemistry for his work on osmotic pressure in solutions and on the laws of chemical dynamics. He was also appointed Chevalier de la Légion d’Honneur (1894), senator of the kaiser-Wilhelm Gesellschaft (1911), and was a member of the Royal Academy of Sciences of Göttingen (1892), the Chemical Society of London (1898), the American Chemical Society (1898), and the Académie des Sciences (1905). In 1911 he died of pulmonary tuberculosis. His body was cremated and the ashes placed in the cemetery at Berlin-Dahlem. He was survived by his wife, Johanna Francisca Mees, whom he had married in 1878, two daughters, and two sons.

Stereochemistry . In 1873 the German chemist Wislicenus published an article on lactic acids, in which he reiterated the view that the only difference between the two optically active forms of the acid must be in the spatial arrangements of the atoms. After van’t Hoff had studied this theory, he published a twelve–page pamphlet, Voorstel tot uitbreiding der tegenwoordig in de scheikunde gebruikte structuur–formules in de ruimte, which included a page of diagrams. Van’t Hoff’s name appeared only at the end of the paper, which was dated 5 September 1874.

At the suggestion of Buys Ballot, professor of physics at Utrecht, the paper was soon translated into French, and the following year van’t Hoff published his views in extended form as la chimie dans I’espace. His revolutionary ideas on the theory of the asymmetric carbon atom did not attract the attention of chemists, however, until Wislicenus asked van’t Hoff’s permission for a German translation by one of his pupils, Felix Herrmann. The translation was published in 1877 as Die Lagerung der Atome im Raume. An English translation by J. E. Marsh appeared in 1891 as Chemistry in space. Then, in 1887, van’t Hoff published Dix années dans I’histoire d’une théorie, in which he pointed out that Le Bel had independently arrived at the same idea, although in a more abstract form.

Both van’t Hoff and Le Bel showed that arrangements of four different univalent groups at the corners of a regular tetrahedron (which van’t Hoff defined as an asymmetric carbon atom) will produce two structures, one of which is the mirror-image of the other. The latter is a condition for the existence of optical isomers, already realized in 1860 by Pasteur, who found that optical rotation arises from asymmetry in the molecules themselves. Van’t Hoff stated that when the four affinities of one carbon atom are represented by four mutually perpendicular directions lying in the same plane, then we may expect two isomeric forms from derivatives of methane of the type CH₂(R₁)₂. Beacuse such isomertic types do not occur in nature, van’t Hoff supposed that the affinities of the carbon atom are directed to the corners of a tetrahedron and that the carbon atom is at the center. In such a tetrahedron a compound of the type CH₂(R₁)₂ cannot exist in two isomeric forms, but for compounds of the type CR₁R₂R₃R₄ it is possible to construct two spatial models that are nonsuperimposable images of one another. In this case there is no center or plane of symmetry for the tetrahedron.

In the first part of the Voorstel, van’t Hoff discussed the relationship between the asymmetric carbon atom and optical activity. Drawing on several examples he showed that all the compounds of carbon that, in solution, rotate the plane of polarized light possess an asymmetric carbon atom (for example, tartaric acid, maleic acid, sugars, and camphor). Then van’t Hoff showed that while the derivatives of optically active compounds lose their rotatory power when the asymmetry of all of the carbon atoms disappears, in the contrary case they usually do not lose this power. Finally he showed that if one makes a list of compounds that contain an asymmetric carbon atom it appears that in many cases the reverse of his first statement is not true, that is, not every compound with such an atom has an influence upon polarized light.

Van’t Hoff’s concepts of the asymmetric carbon atom explained the occurrence of many cases of isomerism not explicable in terms of the structural formulas then current. Moreover, it pointed out the existence of a link between optical activity and the presence of an asymmetric carbon atom. Van’t Hoff also discussed the relationship between the asymmetric carbon atom and the number of isomers. In La chimie dans l’espace he showed that the number of possible isomers of a compound with n inequivalent asymmetric carbon atoms is 2ⁿ, and he indicated how the number of isomers decreased if one or more of the asymmetric carbon atoms is equivalent.

Having introduced the concept of the tetrahedral carbon atom to explain the optical isomerism of a number of organic compounds, van’t Hoff turned in the second and third part of Voorstel to another type of isomerism, which also appeared to be a consequence of the tetrahedral atom, namely, compounds containing doubly and triply linked carbon atoms. A carbon-carbon double bond of the type R₁R₂C=CR₁R₂ is represented by two tetrahedrons with one edge in common, as in the case of maleic and fumaric acids, bromomaleic and bromoisomaleic acids, citraconic and mesaconic acids, crotonic and isocrotonic acids, and chlorocrotonic and chloroisocrotonic acids. Van’t Hoff pointed out that when two tetrahedrons are joined on one edge and R₁, R₂, R₂, and R₄ represent the univalent groups that saturate the remaining free affinities of the carbon atoms, possibilities for isomerism occur when R₁ differs from R₂ and when R₃ differs from R₄. This form of isomerism is now called geometric or cis-trans isomerism. In cases when optical activity was found but the formula was symmetrical, van’t Hoff postulated (usually correctly) either an error in the formula or the presence of an optically active impurity. In 1894 he ventured the opinion, later confirmed, that the occurrence of optically active substances in nature might be the consequence of the action of circularly polarized light in the atmosphere on optically inactive substances.

Although van’t Hoff and Le Bel shared certain views concerning the carbon atom, van’t Hoff was more imaginative and broader in his conceptions and thus incurred harsher criticism, especially from Kolbe, who saw in van’t Hoff’s work a regression of German chemical research to the speculative aspects of Naturphilosophie:

A Dr. J. H. van’t Hoff, of the veterinary school at Utrecht, has as it seems, no taste for exact chemical investigation. He has thought it more convenient to mount Pegasus (obviously loaned by the veterinary school) and to proclaim in his La chimie dans l’espace how during his bold flight to the top of the chemical Parnassus, the atoms appeared to him to have grouped themselves throughout universal space [“Zeichen der Zeit,“in Journal für praktische Chemie, 15 (1877), 473].

He was also criticized by Fittig, Adolf Claus, Wilhelm Lossen, and Friedrich Hinrichsen on the basis that his theories were incompatible with physical laws. Although Wurtz, Spring, and Louis Henry wrote warm acknowledgments, they made no attempt to discuss or criticize his theory. The first to give serious attention to van’t Hoff’s theory was Buys Ballot, who in the journal Maandblad voor natuurwetenschappen (1875) published an open letter to van’t Hoff. His reply, in the same journal, discusses a number of interesting points raised in the letter and includes diagrams of the configurations of the ten isomeric saccharic acids.

In volume I of Ansichten über die organische Chemie van’t Hoff systematically examined the physical and chemical properties of organic substances regarded and classified as derivaties of methane. In volume II he discussed the general relation between the constitution and fundamental properties of organic substances. Especially interested in their physical properties, he attempted to relate stability and reactivity to thermodynamic data, reaction velocities, and chemical equilibriums. Remarkably, van’t Hoff made little use here of his stereochemical ideas.

Physical chemistry. In 1884 van’t Hoff published Études de dynamique chimique, which dealt not only with reaction rates but also with the theory of equilibrium and the theory of affinity based on free energy. In the first section of the book he classified reaction velocities as unimolecular, bimolecular, and multimolecular. He started from the observation (accidentally discovered during his stereochemical researches) that dibromosuccinic acid decomposes at 100°C., a process that he classified as a unimolecular (first-order) reaction. As an example of a bimolecular (second-order) reaction he used the saponification of the sodium salt of monochloric acid, which he had studied in 1883 with his pupil L. C. Schwab: CH₂CLCOOH + NaOH → NaCl + CH₂OHCOONa.

Van’t Hoff recognized the positive-salt effect of the sodium chloride and explained deviations in more concentrated solutions as the variations in volume of the molecules. He also determined the order of chemical reaction for many compounds, for example, the first-order decomposition of arsenic hydride. When arsine is heated, one would expect the chemical equation of its decomposition, to indicate a quadrimolecular reaction . But after having determined the velocity of decomposition, van’t Hoff found that the reaction is of the first order. Thus he discovered that the order may differ from the molecularity, that is, the number of molecules shown in the ordinary chemical reaction equation. Moreover, van’t Hoff found that his researches were complicated by activity factors, reaction milieus, and the movements of the molecules.

Van’t Hoff’s experiments on the influence of temperature on reaction velocity culminated in his famous thermodynamic relationship between the absolute temperature T and the velocity constant K:

where A and B are factors dependent on the temperature, and A is now called the activation energy. To make the relation plausible, van’t Hoff adopted the notion (first used by Leopold von Pfaundler) of chemical equilibrium as the result of two opposite reactions; but van’t Hoff was the first to introduce the double-arrow symbol (still universally used) to indicate the dynamic nature of chemical equilibrium.

After investigating the inflammation temperature at which the reaction takes place, van’t Hoff derived the law of mass action on the basis of reaction velocities—the velocities of the forward and reverse reactions being equal at equilibrium. He also established the general equation for the effect of the absolute temperature T on the equilibrium constant K:

in which q is the heat of reaction at constant volume. The derivation of this equation is not given in the Études. In 1886 van’t Hoff showed that the Clausius-Clapeyron equation (in the form given by Horstmann), which related the temperature coefficient of the vapor pressure to the heat of reaction and volume change, can be generalized in terms of the equilibrium constant, as given above. Since K=k₁/k₂, where k₁ and k₂ are the reaction velocities of the forward and reverse directions,

so that

From this so-called van’t Hoff isochor it follows that the increase or decrease of the equilibrium constant with the absolute temperature depends upon the sign of the reaction heat q at constant volume. Van’t Hoff applied his relation to both homogeneous and heterogeneous equilibriums, to condensed systems (in which no component has a variable concentration), and to physical equilibriums, that is, changes of state.

Van’t Hoff formulated his principle of mobile equilibrium in the limited sense that at constant volume the equilibrium will tend to shift in such a direction as to oppose the temperature change that is imposed upon the system: “Every equilibrium at constant volume between two systems is displaced by fall of temperature in the direction of that system in the production of which heat is developed.“In 1884 Le Châtelier cast the principle in a general form and extended it to include compensation, by change of volume, for imposed pressure changes. This principle is known as the van’t Hoff–Le Châtelier principle.

In the fifth section of his Études, which dealt with affinity, van’t Hoff defined the work of chemical affinity A as the heat q produced in the transformation, divided by the absolute temperature P of the transition point and multiplied by the difference between p and the given temperature T:

The quantity A is now called the maximum external work of the system. By differentiating the equation in respect to T, we find the Gibbs-Helmholtz relation for the dependence of the absolute temperature T on the electromotive force at a constant volume:

Van’t Hoff also established a simple thermodynamic relationship between the osmotic pressure D of the solution and the vapor pressures of pure water S_e and of the solution S_z : D = 10.5 T log S_e / S_z.

At first the the études received little attention. It was neither a textbook nor a purely scientific treatise; it included many new formulas that were presented and applied without derivation. Although the same subjects were discussed in his Vorlesungen über theoretische und physikalische Chemie, the latter work was better arranged and included the results of subsequent research–and thus became a valuable textbook. The proper derivations of the equations in the études appeared in a number of publications. In “L’équilibre chimique dans les systèmes gazeux, ou dissous à l’état dilué” (1886) van’t Hoff showed from quantitative experiments on osmosis that dilute solutions of cane sugar obey the laws of Boyle, Gay-Lussac, and particularly Avogadro.

In his study of solutions, van’t Hoff also investigated their properties in the presence of semipermeable barriers. He extended the quantitative investigation of the botanist Wilhelm Pfeffer (1877), who had contained solutions of cane sugar, and of other substances, within membranes of hexacyanocopper II ferrate, which he formed in the pores of earthenware pots by soaking them first in a solution of copper sulfate and then of potassium ferrocyanide. Van’t Hoff showed that the osmotic pressure P of a solution inside such a vessel immersed in the pure solvent is in apparently direct proportion to the concentration of the solute and in inverse proportion to the volume V of the solution at a given temperature. At a given concentration, P is proportional to the absolute temperature T. The relation serves the general gas law pV = kT.

Van’t Hoff then applied this law thermodynamically to various solutions. He found that the laws of Gay-Lussac, Boyle, and Avogadro are valid only for ideal solutions, that is, those solutions that are diluted to such an extent that they behave like “ideal“gases and in which both the reciprocal actions of the dissolved molecules and the space occupied by these molecules compared with the volume of the solution itself can be neglected.

To the analogy that exists between gases and solutions vam’t Hoff gave the general expression pV = iRT, in which the coefficient i expresses the ratio of the actual osmotic effect produced by an electrolyte to the effect that would be produced if it behaved like a nonelectrolyte. He also arrived at the important generalization that the osmotic pressure that the dissolved substance would exercise in the gaseous state if it occupied a volume is equal to the volume of the solution. Thus he applied Avogadro’s law to dilute solutions. Van’t Hoff determined that the coefficient i has a value of nearly one for dilute solutions and exactly one for gases. He reached this value by various methods, including the vapor pressure and Raoult’s results on the lowering of the freezing point. For dilute solutions of binary electrolytes, such as sodium chloride and potassium nitrate, he found values ranging from 1.7 to 1.9. Hugo de Vries’s experiments with plant cells and Donders’ and Hartog Jacob Hamburger’s experiments with red blood corpuscles produced isotonic coefficients that agreed with van’t Hoff’s.

Thus van’t Hoff was able to prove that the laws of thermodynamics are valid not only for gases but also for dilute solutions. His pressure law gave general validity to the electrolytic theory of Arrhenius, who recognized in the values of i the magnitude that he had deduced, from experiments on electrical conductance, as the number of ions in which electrolytes are divided in solution. Consequently, van’t Hoff became an adherent of the theory of electrolytic dissociation.

In “Lois de l’équilibre chimique dan’s l’état dilué, gazeux ou dissous” (1886) van’t Hoff showed that for many substances the value of i was one, thus validating the relation pV = RT for osmotic pressure. It then became possible to calculate the osmotic pressure of a dissolved substance from its chemical formula and, conversely, the molecular weight of a substance from the osmotic pressure. In “Conditions électriques de l’équilibre chimique” (1886), van’t Hoff gave a fundamental relation between the chemical equilibrium constant and the electromotive force (the free energy) of a chemical process:

in which K is the chemical equilibrium constant, E is the electromotive force of a reversible galvanic cell, and T is the absolute temperature.

While at Amsterdam, van’t Hoff worked on physicochemical problems with a number of his pupils (Johan Eykman, Pieter Frowein, Arnold Holleman, Cohen, and Willem Jorissen) and with foreign chemists who came to Amsterdam to study under him (Arrhenius and Wilhelm Meyerhoffer). Besides his fundamental contributions to thermodynamics of chemical reactions, van’t Hoff also studied solid solutions and double salts. In an important paper on solid solutions, “Ueber feste Lösungen und Molekulargewichtsbestimmung an festen Körpern“(1890), he determined, with the aid of his laws, the molecular weights of the dissolved substance–a solution of carbon in iron or a solution of hydrogen in palladium.

In Vorlesungen über Bildung und Spaltung von Doppelsalzen (1897) van’t Hoff outlined the theoretical and practical treatment of the formation, separation, and conversion of many double salts, especially the tartrates of sodium, ammonium, and potassium. The book also gave a survey of the work in this field by van’t Hoff and by a number of his pupils in the laboratory at Amsterdam.

At Berlin, van’t Hoff studied the origin of oceanic deposits and the conditions of the formation of oceanic salt deposits, particularly those at Stassfurt, from the point of view of Gibbs’s phase rule. He investigated phase equilibriums that form when various quantities of individual salts from the Stassfurt minerals are placed in water that is evaporated at a constant temperature. He also studied the form, order, and quantities of these equilibriums and the effect on them of time, temperature, and pressure. This important theoretical study was of special benefit to the German potash industry. Van’t Hoff’s method generally consisted in determining the fundamental nonvariant equilibriums (consisting of vapor, solution, and three solid phases) that characterize a four-component system at each particular temperature. In this study he was assisted chiefly by Meyerhoffer. Their results were published in the Sitzungsberichte of the Prussian Academy of Sciences and were summarized in van’t Hoff’s two-volume Zur Bildung der ozeanischen Salzablagerungen.

Chemistry is indebted to van’t Hoff for his fundamental contributions to the unification of chemical kinetics, thermodynamics, and physical measurements. He was instrumental in founding physical chemistry as an independent discipline.

BIBLIOGRAPHY

I. Original Works. Van’t Hoff’s doctoral thesis, Bijdrage tot de kennis van het cyanazijnzuur en malonzuur (Utrecht, 1874), was preceded by the publication, a few months earlier, of his important Voorstel tot uitbreiding der tegenwoordig in de schekunde gebruikte structuur-formules in de ruimte; benevens een daarmeê samenhangende opmerking omtrent het verband tusschen optisch actief vermogen en chemische constitutie van organische verbindingen (“Proposal for the Extension of the Formulas Now in Use in Chemistry Into Space: Together with a Related Remark on the Relation Between the Optical Rotating Power and the Chemical Constitution of Organic Compounds”: Utrecht, 1874). It was translated into French as “Sur les formules de structure dans l’espace,” in Archives néerlandaises des sciences exactes et naturelles, 9 (1874), 445–454; and an English version, “Structural Formulas in Space,” appeared in G. M. Richardson, ed., The Foundations of Stereo Chemistry. Memoirs by Pasteur, van’t Hoff, Lebel and Wislicenus (New York, 1901), 37–46.

Van’t Hoff’s views were published in extended form as La chimie dans l’espace (Rotterdam, 1875), trans. into German by F. Herrmann as Die Lagerung der Atome im Raume (Brunswick, 1877, 1894, 1908); and into English by J. E. Marsh as Chemistry in Space (Oxford, 1891) and by A. Eiloart as The Arrangement of Atoms in Space (London-Bombay-New York, 1898).

An enl. ed. of La chimie dans l’espace appeared as Dix années dan l’histoire d’une théorie (Rotterdam, 1887); new ed., Stéréochimie (Paris, 1892). Van’t Hoff’s reply to Buys Ballot is “Isomerie en atoomligging,“in Maandblad voor natuurwetenschappen, 6 (1875), 37–45.

Subsequent writings are Ansichten über die organische Chemie, 2 vols. (Brunswick, 1878–1881); Études de dynamique chimique (Amsterdam, 1884); and “Le’équilibre chimique dans les systémes gazeux, ou dissous ä l’état dilué,“in Archives néerlandaises des sciences exactes et naturelles,20 (1886), 239–302; “Lois de l’équilibre chimique dans l’état dilué, gazeux ou dissous,“in Kungliga Svenska vetenskapsakademiens handlingar, 21 , no. 17 (1886), 3–41; “Une propriété générale de la matiére diluée,“ibid., 42–49; and “Conditions électriques de l’équilibre chimique,” ibid., 50–58; were translated into English in The Foundations of the Theory of Dilute Solutions, Alembic Club Reprints no. 19 (Edinburgh, 1929), 5–42.

Later works are “Die Rolle des osmotischen Druckes in der Analogie zwischen Lösungen und Gasen,“in Zeitschrift für physikalische Chemie, 1 (1887), 481–508; Vorlesungen über Bildung und Spaltung von Doppelsalzen (Leipzig, 1897); Vorlesungen über theoretische und physikalische Chemie, 3 vols. (Brunswick, 1898–1900; 2nd ed., 1901–1903), with English trans. by R. A. Lehfeldt as Lectures on Theoretical and Physical Chemistry, 3 vols. (London, 1899–1900); “Ueber feste Lösungen und Molekulargewichtsbestimmung an festen Köpern in Zeitschrift für physikalische Chemie, 5 (1890), 322-339; Acht Vorträge über physikalische Chemie, gehalten auf Einladung der Universität Chicago, 20 bis 24 Juni 1901 (Brunswick, 1902), with English trans. by A. Smith as Physical Chemistry in the Service of the Sciences (Chicago, 1903); Zur Bildung der ozeanischen Salzablagerungen, 2 vols. (Brunswick, 1905–1909); and Die chemischen Grundlehren nach Menge, Mass und Zeit (Brunswick, 1912).

Van’t Hoff contributed to E. Cohen and H. Precht, eds., Untersuchungen über die Bildungsverhältnisse derozeanischen Salzablagerungen, insbesondere des Stassfurter Salzlagers (Leipzig, 1912), published after his death. His 1901 Nobel Prize lecture, “Osmotic Pressure and Chemical Equilibrium,“is in Nobel Lectures. Chemistry, 1901–1921 (Amsterdam-London-New York, 1966), 5–10.

II. Secondary Literature. The most comprehensive study of van’t Hoff’s life and work is E. Cohen, Jacobus Henricus van’t Hoff. Sein Leben und Werken (Leipzig, 1912), with complete bibliography, 598–622. His professorship at Amsterdam is extensively described in W. P. Jorissen and L. T. Reicher, J. H. van’t Hoffs Amsterdamer Periode 1877–1895 (Den Helder, 1912). Achille Le Bel’s 1874 article is “Sur les relations qui existent entre les formules atomiques des corps organiques et le pouvoir rotatoire de leurs dissolutions,“in Bulletin de la Société chimique de Paris,, 22 (1874), 337–347: C. H. D. Buys Ballot’s open letter is “Openbare brief aan Dr. J. H. van’t Hoff,“in Maandblad voor natuurwetenschappen, 6 (1875), 21–28.

There are obituary notices by H. C. Jones, in Proceedings of the American Philosophical Society, 50 (1911), iii-xii: W. Ostwald, in Berichte der Deutschen chemischen Gesellschaft, 44 (1911), 2219–2252; F. G. Donnan, in Proceedings of the Royal Society of London, 86A (1912), xxxix-xliii: and J. Walker, in journal of the Chemical Society, 103 (1913), 1127–1143. See also H. A. M. Snelders, “The Birth of Stereochemistry. An Analysis of the 1874 papers of J. H. vant’t Hoff and J. A. le Bel,“in Janus, 60 (1973), 261–278; and “The Reception of J. H. van’t Hoff’’s Theory of the Asymmetric Carbon Atom,” in Journal of Chemical Education, 51 (1974), 2–7.

H. A. M. Snelders