(b. Glasgow, Scotland, 21 December 1805; d. London, England, 16 September 1869)
The son of a prosperous manufacturer, Graham entered the University of Glasgow in 1819, at the age of fourteen, and was convinced by the lectures of Thomas Thomson that his calling lay in the field of chemistry. His father, who wanted him to become a minister of the Church of Scotland, was opposed to this choice of vocation, but Graham received encouragement and help from his mother and sister. After receiving the M.A. at Glasgow in 1826, he worked for nearly two years in the laboratory of Thomas Charles Hope at the University of Edinburgh. He then returned to Glasgow, where he taught mathematics and chemistry in a private laboratory. In 1829 he became assistant at the Mechanics’ Institution, and in 1830 he succeeded Alexander Ure as professor of chemistry at Anderson’s College (later the Royal College of Science and Technology), where he produced his classic work on the phosphates and arsenates (1833).
In 1834 Graham became a fellow of the Royal Society. Three years later he succeeded Edward Turner as professor of chemistry at the University College, London (later the University of London). His time was then fully occupied in teaching, writing, advising on chemical manufactures, and investigating fiscal and other questions for the government. In 1841 he participated in the founding of the Chemical Society and became its first president. With the death of John Dalton in 1844, Graham was left as the acknowledged dean of English chemists, the successor of Joseph Black, Joseph Priestley, Henry Cavendish, William Wollaston, Humphry Davy, and John Dalton. He resigned his professorship in 1854 to succeed Sir John Herschel as master of the mint, a post which ceased to exist upon Graham’s death. He died in 1869, an indefatigable but physically broken man.
As a lecturer Graham was well liked by his students, but he was somewhat nervous and hesitant. He was much in demand as a consultant. Most of his work lay in the field of inorganic and physical chemistry, and he is recognized as the real founder of colloid chemistry. His work, usually quantitatively accurate, was original in conception, simple in execution, and brilliant in the results to which it led. Much of his earlier experimental work, some of it not very accurate, is said to have been performed by students and assistants. He received the Royal Medal of the Royal Society twice (1837 and 1863), the Copley Medal of the Royal Society (1862), and the Prix Jecker of the Paris Academy of Sciences (1862). His original and admirable textbook Elements of Chemistrywas widely used, not only in England but also on the Continent, in its much enlarged multivolume translation by Friedrich Julius Otto.
Graham’s first original paper, which appeared during his twenty-first year, dealt with spontaneous gas movement, a subject that occupied him throughout his career. In fact, almost all his research is but a development, in different directions, of his early works on gaseous diffusion and water of hydration, as when he showed that Henry’s law is not valid for very soluble gases. In another work he found that, like potash, ammonia forms a normal oxalate, binoxalate, and quadroxalate, but that soda forms only a normal oxalate and binoxalate. He also made interesting observations on the glow of phosphorous and the spontaneous flammability of phosphine.
In 1829 Graham published the first of his papers relating specifically to the subject of gaseous diffusion. Although this publication contains the essentials of Graham’s law, known to every student of general chemistry, it was in a subsequent paper, for which he was awarded the Keith Prize of the Royal Society of Edinburgh, that he definitely established the principle:
The diffusion or spontaneous intermixture of two gases in contact is effected by an interchange in position of indefinitely minute volumes of the gases, which volumes are not necessarily of equal magnitude, being, in the case of each gas, inversely proportional to the square root of the density of that gas... diffusion takes place between the ultimate particles of gases, and not between sensible masses [“On the Law of the Diffusion of Gases,” in Philosophical Magazine, 2 (1833)].
Graham maintained that by means of this law the specific gravity of gases could be determined, through experiments on the principle of diffusion, with greater accuracy than by ordinary means. He also pointed out that mixtures of gases could be separated by diffusion, a process employed during World War II at Oak Ridge, Tennessee, to separate the fissionable isotope uranium 235 from the nonfissionable isotope uranium 238.
Graham also measured the effusion of gases through a small hole in a metal plate and found the velocities of flow to be inversely proportional to the square roots of the densities. Yet in his study of the rates of transpiration of gases through capillary tubes, he found that the rates became constant with a certain length of tube and were not simply related to the densities. Later in his career, in “On the Absorption and Dialytic Separation of Gases by Colloidal Septa,” Graham began his studies of the penetration of hydrogen through heated metals, a phenomenon which he called “occlusion” and which he explained first by liquefaction of hydrogen and its dissolution in the metal. He later supposed hydrogen to be the vapor of a very volatile metal, hydrogenium, which forms an alloy with the metal. In 1863 he even suggested that the various chemical elements might “possess one and the same ultimate or atomic molecule existing in different conditions of movement.”
Graham’s major contribution to inorganic chemistry is his paper “Researches on the Arseniates, Phosphates, and Modifications of Phosphoric Acid,” in which he elucidated the differences between the three phosphoric acids. This research and the style of the paper are reminiscent of Joseph Black’s work on magnesia and the alkalies carried out in Glasgow eighty years earlier. Graham’s discovery of the polybasicity of these acids provided Justus Liebig with the clue to the modern concept of polybasic acids. Of this classic work the eminent German chemist and historian of chemistry Albert Ladenburg has said, “so much has seldom been accomplished by a single investigation.” Nevertheless, J. J. Berzelius insisted that the three phosphoric acids were isomers of P2 O5 and as late as 1843 he wrote that Graham’s “point of view lacks justification in several respects.”
Before Graham’s work the relationship between the various phosphates and phosphoric acids was a subject of the greatest confusion. Compounds of one and the same anhydrous acid with one and the same anhydrous base, in different proportions, had long been known, but Graham was the first to establish the concept of polybasic compounds, that is, a class of hydrated acids with more than one proportion of water replaceable by a basic metallic oxide so that several series of salts could be formed. Graham concluded that the individual properties of the phosphoric acids could not be expressed if they were regarded as anhydrides; they must contain chemically combined water essential to their composition. He therefore designated the three modifications of phosphoric acid as phosphoric acid, , that is, 3HO. PO 5 (modern, 3H2 O. P2 O5 or H3 PO4); pyrophosphoric acid, i.e., 2HO.PO 5 (modern, 2H2 O. P2 O5 or H4 P2 O7); and metaphosphoric acid, i.e., HO. PO5 or (modern, H2 O.P2 O5 or HPO3). In other words, he regarded them respectively as a triphosphate, a biphosphate, and a phosphate of water.
When one of these compounds is treated with a strong base, the whole or a part of the water is supplanted, but the amount of base in combination with the acid remains unaltered. There are thus three sets of phosphates, in which the oxygen in the acid being five, the oxygen in the base is three, two, and one [“Researches on the Arseniates...” in Philosophical Transactions of the Royal Society, 123 (1833)].
Graham summarized the compositions of the three acids of phosphorus and of their sodium salts as shown below. Just as in his demonstration of the relationships to one another of phosphoric acid and the three sodium phosphates, Graham originated the concept of polybasic compounds; so, in his demonstration that the pyrophosphates and metaphosphates are compounds differing from the phosphates by loss of water or metallic base, he originated the concept of anhydro compounds.
Although some isolated investigations on colloids had been carried out before Graham, his publications in this field laid the foundations of colloid chemistry. In “On the Diffusion of Liquids,” Graham applied to liquids the exact method of inquiry he had applied to gases twenty years before, and he succeeded in placing the subject of liquid diffusion on about the same footing as that to which he had raised the subject of gaseous diffusion prior to the discovery of his numerical law. He showed that the rate of diffusion was approximately proportional to the concentration of the original solution, increased with rise in temperature, and was almost constant for groups of chemically similar salts at equal absolute (not molecular) concentrations and different with different groups. He believed that liquid diffusion was similar to gaseous diffusion and vaporization with dilute solutions, but with concentrated solutions he noted a departure from the ideal relationship, similar to that in gases approaching liquefaction under pressure. Based on his work on osmosis, Graham developed what he called a “dialyzer” which he used to separate colloids, which dialyzed slowly, from crystalloids, which
|Oxygen in Soda Water Acid||Modern Formulation|
|First Class||Phosphoric acid|
Biphosphate of soda
Phosphate of soda
Subphosphate of soda
|Second Class||Pyrophosphoric acid|
Bipyrophosphate of soda
Pyrophosphate of soda
|Third Class||Metaphosphoric acid|
Metaphosphate of soda
dialyzed rapidly. He prepared colloids of silicic acid, alumina, ferric oxide, and other hydrous metal oxides, and he distinguished between sols and gels.
Much of the terminology and fundamental concepts of this field are due to Graham:
As gelatine appears to be its type, it is proposed to designate substances of the class as colloids [κόλλα glue], and to speak of their particular form of aggregation as the colloidal condition of matter. Opposed to the colloidal is the crystalline condition. Substances affecting the latter form will be classed as crystalloids… Fluid colloids appear to have always a pectous [πηκτός, curdled] modification; and they often pass under the slightest influences from the first into the second condition... The colloidal is, in fact, a dynamical state of matter; the crystalloid being the statical condition.
Graham stated that crystals and crystalloids “appear like different worlds of matter,” but he recognized that the essential difference is in the state and that the same substance can exist in the crystalloid or colloid state. He concluded that “in nature there are no abrupt transitions, and the distinctions of class are never absolute.”
I. Original Works. Graham’s writings include “On the Absorption of Gases by Liquids,” in Annals of Philosophy, 12 (1826). 69; “A Short Account of Experimental Researches on the Diffusion of Gases Through Each Other, and Their Separation by Mechanical Means,” in Quarterly Journal of Science and the Arts (Royal Institution), 27 (1829), 74; “On the Law of the Diffusion of Gases,” in Philosophical Magazine2 (1833), 175–269, 351; “Researches on the Arseniates, Phosphates, and Modifications of Phosphoric Acid,” in Philosophical Transactions of the Royal Society, 123 (1833), 253, repr. as Alembic Club Reprint no. 10 (Edinburgh, 1961); Elements of Chemistry, Including the Application of the Science in the Arts (London, 1842), trans into German and enlarged by F. J. Otto as Ausführliches Lehrbuch der Chemie, physikalische, anorganische, organische (Brunswick, 1854–1893); “On the Motion of Gases,” in Philosophical Transactions of the Royal Society, 136 (1846), 573, and 139 (1849), 349; “On the Diffusion of Liquids,” ibid., 151 (1861), 183–224; “Speculteive Ideas Respecting the Constitution of Matter,” in Proceedings of the Royal Society, 12 (1863), 620–623; “On the Absorption and Dialytic Separation of Gases by Colloidal Septa,” in Philosophical Transactions of Royal Society, 156 (1866) 399–439; and “On the Occlusion of Hydrogen Gas by Metals,” in Proceedings of the Royal Society16 (1868), 422.
II. Secondary Literature. Discussions of Graham’s life and work are W. Odling, in Report of the Board of Regents of the Smithsonian Institution (1871), pp. 171–216. repro in E. Farber” ed., Great Chemists (New York, 1961), pp. 553–571; J. R. Partington, A History of Chemistry, IV New York, 1904), 265–270, 272–275, 729–732; and M. Speter, “Graham, “in G. Bugge, ed., Das Buch der grossen Chemiker, II (Weinheim, 1965), 69–77. Discussions of Graham’s law are E.A. Mason and R.B Evans, “Graham’s Law: Simple Demonstrations of Gases in Motion. Part I, Theory. Part, II, Experiments,” in Journal of Chemical Education, 46 (1969), 359–364, 423–427; E.A Mason and B. Kronstadt, “Graham’s Law of diffusion and Effusion,” ibid., 44 (l967). 740’-744; and A. Ruckstuhl, “Thomas Graham’s Study of the Diffusion of Gases,” ibid, 28 (l951). 594–596.
George B. Kauffman
Thomas Graham, 1805–69, Scottish chemist, best known for research in diffusion in both gases and liquids that led to his formulation of Graham's law. His discovery that certain substances (e.g., glue, gelatin, starch) pass through a membrane more slowly than others (inorganic salts, e.g., common salt, or sodium chloride) led him to draw a distinction between the two groups, calling the former (the slower) colloids and the latter crystalloids. In this connection he discovered dialysis. His work was the earliest in colloidal chemistry. His investigation of phosphoric acid led to the present chemical concept of polybasic acids.