1 2 0 D O C . 7 2 P O R E S I Z E O F F I L T E R S Published in Deutsche medizinische Wochenschrift 49 (1923): 1012–1013. The manuscript was com- pleted before 2 July (see Doc. 73). Published 3 August 1923. Heinrich Bechhold (1866–1937) was director of the Institut für Kolloidforschung in Frankfurt am Main. For his description of the flow-through velocity (Durchflussgeschwindigkeit) method, see, e.g., Bechhold 1908, pp. 339–341. Eugen de Haën (1835–1908) was a chemist, founder of E. de Haën & Comp., Fabrik pharmazeutischer und technischer Chemikalien, in List near Hannover. Charles Chamberland (1851–1908) was a French microbiologist. He invented his porcelain bar filter (“Filtre Chamberland—Système Pasteur”) in 1884. Wilhelm Berkefeld (1836–1897) was founder of the Firma Berkefeld Filter in Celle. Wilhelm Pukall (1860–1937) was director of the Königliche kera- mische Fachschule in Bunzlau, inventor of the Pukall clay filter. When Mühsam presented the results of the paper in his lecture to the Deutsche Vereinigung für Mikrobiologie, he attributed the idea to Einstein (Mühsam, H. 1923). The method had been earlier described by Bechhold in 1908 (Bechhold 1908). A comparison of the results obtained by Bechhold and those obtained by Einstein and Mühsam is found in Mysels 1989. Einstein had a longstanding interest in the phenomenon of capillarity and the explanation of cap- illary forces, which goes back to his student days and his first scientific publication (Einstein 1901 [Vol. 2, Doc. 1]. See also Vol. 2, the editorial note “Einstein on the nature of molecular forces”). Cap- illarity and molecular forces was also the subject matter of Einstein 1911a (Vol. 3, Doc. 12), and cap- illarity is a topic mentioned twice in his Scratch Notebook, 1910–1914? (see Vol. 3, Appendix A, p. 567 and p. 574).