GERMAIN HENRI HESS AND THE FOUNDATIONS OF THERMOCHEMISTRY' HENRY M. LEICESTER College of Physicians and Surgeons, San Francisco. California
TmxMocHEMwms had its beginning in the studies of Lavoisier and Laplace which established the fact that the heat absorbed in a reaction is equal to the heat liberated in the reverse reaction. This work was not, followed up, and chemists in the first half of the nineteenth century were mostly concerned with the 'nalysis and reactions of inorganic and organic compounds. Heat mas a subject which was left to the physicist,. The work of Germain Henri Hess was therefore the more original, since he pioneered in a field which his contemporaries vere neglecting almost completely. His own training had done nothing to prepare him for thermochemical studies, since it was exactly that of all the chemists of his day. In fact, he was well known among his colleagues for a wide variety of studies in both inorganic and organic chemistry before he undert,ook his vork in thermochemistry. Today, however, the situation is reversed, and his other work is forgotten. Only his name is now remembered, and this only in connection mith his chief generalization-the Hess law. Hess mas horn in Geneva on July 26, 1802 ( I ) , but at the age of three he mas taken to St. Petershurg, where his father vas a teacher, and almost all of his life was spent in Russia. In 1822 he entered the medical faculty of the University of Dorpat, then one of the leading universities of Russia. Although his studies were chiefly medical, he found time to obtain a thorough t,raining also in chemistry and geology. His thesis for the degree of Doctor of Medicine was on a chemical topic, "Studies of the chemical composition and medicinal action of the mineral waters of Russia." He obtained his degree in 1825, and then decided to go to Stockholm to study chemistry in more detail with Aerzelius. On December 9, 1825, the latter wrote to Wohler, "Osann, who is coming here from Dorpat, has sent me another student, Dr. Hess, a young man of much promise. He has a good head, seems to have a foundation of knowledge, much attentiveness, and a particular zeal" (t). Hess's stay in Stockholm was brief, however, for on January 13, 1826, Berzelius wrote. "Hess, who came here from Dorpat, has gone away again, compelled to return by domestic affairs. I was well pleased with him" (3). In spite of the shortness of his stay with Berzelius, Hess remained friendly with the great Swedish chemist throughout his life, and mas -
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the Edger Fahs Smth Cailectmn. Un~uerr:ky of Pennsylvania Oarmain H.nri H e u
often mentioned in the letters Berzelius wrote to his various correspondents. The interests of Berzelius in mineral chemistry and chemical analysis were also those of Hess, and all his early work was done in these fields. In this he was following in the path of most of the Russian chemists of his time, for, after the days of Lomonosov, theoretical studies had been practically abandoned in Russia, and almost all attention was centered on the discovery of new minerals. Following his return to Russia, Hess accompanied a geological expedition to the Urals, and then settled in Irkutsk, where he took up a medical practice. In addition to the duties of his practice, which included studies on the prevention of eye disorders which were very common in the region, he found time to continue his geological and chemical studies. As a result of his descriptions and analyses of minerals and waters from various parts of Russia, he was elected an adjunct member of the Academy of Sciences of St. Petersburg in 1828, and in 1830 he was chosen as an extraordinary Academician. Upon receiving this honor, he ahandoned his medical practice and settled in St. Petersburg, where he devoted the rest of his life to rhemistry.
' Presented before the Division of the History of Chemi~trya t t,he 119th Meeting of the American Chemical Society, Boston, April 3,1951. I
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The following ten years were filled with activity. He signalized his membership in the Academy with a summary of his work a t Irkutsk, "On the common salt of the Irkutsk Government," in which he showed that the sodium chloride from this area contained a high proportion of potassium, magnesium, and aluminum. He also undertook a study of the composition of the water of the Neva River which flows through St. Petersburg. He discovered a number of new minerals, and proved the composition of the oxide of cobalt CosOa, a study which was later confirmed by Berzelius. His work on the natural resources of Russia led him to analyze natural gas from Baku, and various resins and waxes. He thus became interested in methods of organic analysis and in problems of organic chemistry. His main contribution in this field was his study of the oxidation of sugars by nitric acid, which led t o his discovery of saccharic acid. When Hess came to St. Petersburg, the Technological Institute had just been organized, and he was appointed to a Commission to plan the course in practical and theoretical chemistry. He was appointed to the chair of chemistry in this school soon afterward. As new institutions of higher learning were organized, he began to teach in these also. I n 1832 he joined the faculties of the Mining Institute and the Chief Pedagogical Institute, and in 1838 he added the course a t the Artillery School to his other teaching duties. I n the Chief Pedagogical Institute, which ;rained teachers for most of Russia, one of his students was A. A. Voskressenskil, who later became Professor of Chemistry in the same Inst,itute, and in this capacity taught chemistry to Mendeleev. As a result of his teaching duties, Hess began to work on a texthook'of chemistry soon after he reached St. Petersburg. This work, "Fundamentals of Pure Chemistry," was published in two volumes by the Academy of Sciences from 1831 to 1833. It did much to establish a rational nomenclature for chemistry in the Russian language. I n 1834, Hess published a one-volume abridgement to serve as a more usable textbook, and this went through seven editions, the last of which appeared in 1849. I t became the standard Russian text in chemistry until the appearance of Mendeleev's two texts, "Organic Chemistry" in 1861, and "Fundamentals of Chemistry" in 1868-70. In addition to his research and teaching duties, Hess also found time t o serve on government commissions relating to the teaching of chemistry and the establishment of a water supply for St. Petersburg. In 1834 he was made an ordinary Academician of the Academy of Sciences. In 1838, Hess began the series of studies on which his fame chiefly rests. In a paper, "The evolution of heat in multiple proportions" (4), he showed that the various hydrates of sulfuric acid could be detected by the heat evolved in their fo~mation. In 1840 he published a full statement of his law, both in French in the Bulletin of the Acudemy of Sciences of St. Petersburg, and in German in Poggendorf's Annalen der Chemie und
JOURNAL OF CHEMICAL EDUCATION
Physilc (5). He showed that not only for the formation of hydrates of sulfuric acid, but also for the heat of formation of ammonium sulfate in water solution and the neutralization of hydrochlonc acid by sodium and potassium hydroxides, the amount of heat developed mas always the same, regardless of whether the process went directly or proceeded through a number of intermediate steps. This "law of the constant summation of heat" obviously showed hov to determine the heat of reactions which had not been measured directly, and it lies a t the basis of all later work in thermochemistry. It is a remarkable fact that, although it clearly depends on the law of conservation of energy, this law had not been announced at the time Hess Kas making his studies, and was not actually stated until two years later, by Meyer in 1842. Hess fully appreciated the significance of his law, and did not hesitate to make practical applications of it. An excellent illustration is found in a letter he wrote to Arago in 1840 (6). At that time, the heating power of coal was estimated by determining the amount of oxygen required to burn it. The English chemist, Ure, observed that the more hydrogen a coal contained, the less heat it gave off, and so the oxygen method did not give an accurate measure of the heating power. Ure explained this by assuming that the vapors formed in burning the coal absorbed heat. Hess pointed out the error of this assumution, and wrote: The sum of the heat corresponding to a. certain amount of water and carbonic acid which me suppose arises from combustion, being cmzslant, it is evident that if hydrogen is found previously combined with carbon, this comhination cannot have occurred without evolution of heat; this amount, already eliminated, cannot be recovered in the quantity evolved by the defined combustion. There results in practice the simple rule: that a cornbustible comprmnd always arolves less heat than do ils elements laken separately. . . . I have the full conviction that we will have a. precise idea of chemical phenomena only when we succeed in indicating in our formulasthe ratios of heat relations as we indicate today the relative numbers of ponderable atoms; at least thermochemistry promises to disclose the still secret laws of affinity.
Continuing his studies, Hess vas led in 1842 to his second major law, the "law of thermoneutrality." This states that in exchange reactions of neutral salts in water solution, no heat effect is observed. Hess himself was unable to explain this fact in a satisfactory manner, and it was not until the announcement of the Arrhenius theory of electrolytic dissociation in 1887 that the explanation became apparent. After this time, Hess became less active in research, and progressively fewer papers appeared from his pen. He served actively on committees of the Academy of Sciences, and helped other chemists to obtain recognition for their work. It was largely through his interest that Karl Klaus, a rather obscure chemist a t the University of Kazan, was able to gain recognition for the discovery of ruthenium. Hess and Fritsche, another Academician, were instrumental in securing for Klaus the Demidov prize, a major scientific award in Russia a t that period. Hess continued his teaching activity, and besides his
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work in the various institutions, he was entrusted with the training of the Czarevich Alexander in chemistry. I n 1838, Berzelius wrote Wohler a description of a visit to his laboratory by the Czarevich, who was then touring Sweden (7). Alexander told Berzelius that Hess had taught him chemistry from the Berzelius "Lehrbuch," and Alexander was "fairly well versed in it." I n parting, the royal visitor gave Berzelius a valuable ring as a gift. Berzelius closed his letter with the remark, "I would gladly have such a visit every week." By 1848 the health of Hess began to give way, and he resigned most of his teaching duties. He made an inspection of the newly opened sugar factories in the south of Russia in that year, but this was almost his last public duty. He died on November 30, 1850, at the early age of 48. His work mas not continued by any other Russian chemist, and, in fact, thermochemistry was generally neglected for another decade. Then began the elaborate series of investigations of heats of reaction by Berthelot in France and Thomsen in Denmark. The mass of data accumulated by these investigators confirmed the truth of the Hess law again and again, but almost nothing was said of Hess himself, and chemists forgot the man whose work lay a t the foundation of all the new material which was appearing. The work of Hess was once more brought to light by Wilhelm Ostwald, who had begun his own career a t
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Riga and Dorpat, and had probably there heard of Hess. I n his "Textbook of General Chemistry," published in 1887, Ostwald began the section on thermochemistry with a full account of the contributions of Hess in this field, and later he reprinted the most important papers of Hess in his series Klassiker der exacten Wissenschaften ( 8 ) . I t is strange, however, that, unlike most of the volumes in this series, the volume on Hess does not contain any biographical material. Thus, while the contributions of Hess are now recognized, and his name is firmly attached to the law which he first announced, the details of his life have been difficult to obtain. LITERATURE CITED (1) Most of the biographical material on Hess is in Russian. The "Brokhauschief sources used here were: V. YAKOVLEV, Efron Encyolopedio Dictionary," St. Petersburg, 1892, Vol. 8, pp. 583-4; and P. WALDEN,"A Sketch of the History of Chemistry in Rus~ia,"Odessa, 1917, pp. 412-8, 456-9. O., "Briefwech~elzwischen J. Berzelius und F. (2) WALLACH, W&Ier," Leipzig, 1901, Vol. 1, p. 98. (3) Ibid.,pp. 108-9. (4) Pogg. Ann., 47,210(1839). (5) Ibid,, 50,385 (1840). (6) Complesrad., 10,759-63 (1840). (7) WALLACE, O., op. tit., V d . 2, p. 40. W., "Thermoohemisehe Untersuchungen van G . H. (8) O~TWALD, Hess 183S1842," Klassikerderizaeten Wi'issensehaflen, No. 9, Leipzig, 1890.
