J.H. van ’t Hoffs theorie van de verdunde oplossingen (1886)

Abstract

J.H. van 't Hoffs theory of diluted solutions (1886) In his Etudes de dynamique chimique (1884).J.H. van 't Hoff was confronted with the problem of the magnitude of the attraction of water by salts. He wondered whether it is possible to measure this force, i.e. the affinity, in the simple case of an aqueous solution. Hugo de Vries drew his attention to Wilhelm Pfeffer's experiments on osmotic pressure. This led to van 't Hoffs theory of osmotic pressure, which he formulated in 1884-1885 and which was published in 1885-1887. Van 't Hoff found an analogy between the osmotic pressure and the gas pressure. The general gas law PV=RT is also applicable to dilute solutions, although for electrolytes a factor i had to be introduced: PV=iRT. It was Svante Arrhenius who suggested that i is equal to the number of ions. In 1887 Arrhenius published his theory of electrolytic dissociation. Connected with van 't Hoffs theory of osmotic pressure, the definitive formulation of the theory of dilute solutions was obtained. Soon discussions were held about the theory of solutions. The British Association for the Advancement of Science organized a meeting in Leeds in 1893 where the new theories were fiercely attacked by a number of British scientists. In April 1893 the meeting of the Nederlandsch Natuur- en Geneeskundig Congres (Dutch Physical and Medical Congress) in Groningen reached favourably to the new ideas, On January 8, 1894, van 't Hoff lectured on the genesis of the theory of solutions before the Deutsche Chemische Gesellschaft in Berlin. It is remarkable that he asked himself whether the theory of electrolytic dissociation conforms to reality. Although his student Jacob Jan Alexander Wijs had determined the value of the dissociation constant of water (1893), van 't Hoff ended his lecture with the intriguing question: "Is the theory of electrolytic dissociation proved in this way? By no means. But it wholly unexpectedly has supplied much in the field of saponification." It is not clear whether Van 't Hoff had his doubts on the degree of reality of the theory of electrolytic dissociation or whether he did not want to take the risk of a confrontation with his opponents.