Determination of the Avogadro constant by counting the atoms in a 28Si crystal.

The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by counting the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, NA = 6.022,140,78(18) × 10(23) mol(-1), is the most accurate input datum for a new definition of the kilogram.

[The private institute of Franz Wilhelm Schweigger-Seidel (1795-1838) in Halle]. / Das Privatinstitut von Franz Wilhelm Schweigger-Seidel (1795-1838) in Halle.

The aim of this paper is to describe the development of the chemical-pharmacist institute of Franz Wilhelm Schweigger-Seidel (1795-1838) in Halle. The institute was founded in 1829. Six letters by Johann Salomo Christoph Schweigger (1779-1857) and Franz Wilhelm Schweigger-Seidel to Johann Bartholomäus Trommsdorff (1770-1837) present new detailed information on the institute of Schweigger-Seidel and on his biography, especially on his descent and on his work as a pharmacist. Besides it was possible to show the family links between him and J. S. Chr. Schweigger resulting from adoptation in a correct way for the first time.

["I would like to so much--but then also; but, but--!!!"--torment of a private lecturer at the beginning of the 19th century]. / "Ich will so gern--und kann auch wol--; aber, aber--!!!"--die Misere eines Privatdozenten zu Beginn des 19. Jahrhunderts.

The biography of Carl Friedrich August Theodor Kastner (1797-after 1841), the brother of the famous chemist and teacher of Justus von Liebig (1803-1873) Karl Wilhelm Gottlob Kastner (1783-1857), is an interesting example of the difficult situation of outside lecturers at the universities in the first half of the 19th century; a big group of scientists, which are absolutely underrepresented in the source material and in the historiography too. This paper tries to show the facts and the backgrounds for the problems in the career of outside lecturers.

["My contribution to humanity". The work of the Prussian lay physician Arthur Lutze (1813-1870)]. / "Diese Bitte war ich der Menschheit schuldig"-Das Wirken des homöopathischen Laienheilers Arthur Lutze (1813-1870) in Preuben.

The aim of this paper is to describe the life and work of the homeopathic lay physician Arthur Lutze (1813-1870), particularly his work in Prussia. The paper also helps explain the extraordinary popularity of non-medical practitioners during this period. Lutze's years in Prussia were fundamental for his homeopathic ambitions, since they afforded him access to many of the renowned homeopaths of the period. Lutze gained popularity by focusing his practice on the common people. Even though he was not licensed and he collaborated with unknown non-medical practitioners, Lutze gained legitimacy through the work of properly certified doctors.