(b. Budapest, Hungary, 16 May 1878; d. Mosonmagyaróvár, Hungary, 18 August 1945)
Szily came from a family of physicians. His father, Adolf Szily, was a doctor and director of a Budapest hospital, and his older brother became a professor of ophthalmology at the University of Budapest. Szily studied medicine at the University of Budapest and after obtaining his medical degree became an assistant at the Institute of Physiology there, where he carried out his fundamental research on the colorimetric determination of hydrogen ion concentration.
Since the time of Robert Boyle various plant juices had been used to determine whether a liquid was acidic or basic. When synthetic substances were introduced as indicators, it was observed that they did not change color at the same level of acidity as the natural juice indicators. On the basis of Arrhenius’ theory of ionization (1887), Wilhelm Ostwald introduced the concept of the dissociation constant with a view to ascertaining the strengths of acids and bases as a function of, respectively, hydrogen ion and hydroxyl ion concentration. He also determined the value of the dissociation constant of water. In 1893 Max Le Blanc invented the hydrogen electrode, which made it possible to measure the hydrogen ion concentration electrochemically.
It appears, however, that for a long time chemists were unable to recognize the significance of these developments. They did not comprehend the difference between titrimetrically determinable amounts of acid and the strengths of acids, for most of them dealt only with the former. Physiologists and biologists, however, were more concerned with the strengths of acids, since small changes in acidity play a great role in various life processes. They were therefore the ones to elucidate the concepts underlying the treatment of these questions and to develop appropriate techniques of measurement. The first to do so was Szily, who in 1903 published “Indikátorak alkalmazásáól állati folyadékok vegyhatásának meghatározására” (“Application of Indicators in the Determination of the Reaction of Animal Fluids”), in Orvosi Hetilap, 45 (1903), 509–518. After establishing that the reaction of animal fluids–the hydrogen ion concentration of blood serum, for example–can-not be determined titrimetrically, Szily hit upon the idea of using the indicators for this purpose, since each indicator changes color at a specific hydroxyl ion concentration, regardless of the nature of the base. By using various indicators he was able to establish a scale for estimating acidity. In addition, employing seven different indicators, he devised a scale for making an approximate determination of the acidity of the blood serum. In the course of this research he also determined the resistance of blood serum to the effects of acids and bases (its buffer property).
In 1903 Szily lectured on his results before the Physiology Society of Berlin; and Hans Friedenthal, a lecturer at the University of Berlin, arranged for Szily to continue his research there. Friedenthal began investigations in the same area and perfected Szily’s method by using a larger number of indicators and by employing standard (buffer) solutions of precisely known hydrogen ion concentration. In 1904 he reported that he had been unsuccessful in his attempt to produce these solutions by successive dilution of acidic or basic solutions. Szily suggested that he prepare stable solutions of reliable hydrogen ion concentrations by mixing primary and secondary phosphates in different proportions. Szily was, consequently, the inventor of artificial buffer solutions. Research in this area was extended by S. P. L . Sørensen, who introduced the concept of pH in 1909.
In 1905 Szily transferred to the surgery clinic of the University of Budapest, and in 1909 he became director of the serological and bacteriological laboratory of the Budapest Jewish Hospital. Henceforth his research was of a purely medical nature. He investigated the therapeutic effects of Salvarsan and communicated his findings to Paul Ehrlich, who followed with interest the results of the introduction of the drug into Hungary. During World War I, Szily directed an army epidemiological unit and was concerned with typhus theraphy and the treatment of equine influenza through vaccination. After the war he published studies on protein therapy, but his scientific activity was steadily eclipsed by the demands of his private practice in Budapest. His practice seems to have disappointed him, for in 1928 he went to the small city of MosonmagyarÓvÁr as urologist with the state health insurance administration.
After the Nazi assumption of power in Hungary, Szily, a diabetic, was taken in 1944 to the concentration camp at Györ. During the last days of the war in Hungary he escaped deportation to Germany through his professional connections. He returned to his post in Mosonmagyaróvár but, unable to secure sufficient medication, died soon afterward.
I. Original Works. Szily was author of thirty chemical and medical publications, including the one mentioned above. His medical publications appeared generally in Wiener Medizinische Wochenschrift and Berliner Klinische Wochenschrift in 1910–1919.
II. Secondary Literature. See F. Szabadváry, “Development of the pH concept. A historical survey,” in Journal of Chemical Education, 41 (1964), 105–107; History of Analytical Chemistry (Oxford, 1966), 363, 376–377; and “Szily Pál (1878–1945),” in Orvossörténeti Közlemények (Communicationes de historia artis medicinae), 38 (1966), 121–130, in Hungarian.
Hans Friedenthal’s report is “Die Bestimmung der Reaktion einer Flüssigkeit mit Hilfe von Indikatoren,” in Zeitschrift für Elektrochemie, 10 (1904), 113–119.