1874 | Science
Science
German physicist F. W. G. (Friedrich Wilhelm Georg) Kohlrausch, 33, demonstrates that an electrolyte has an amount of electrical resistance that is both definite and constant (see Hittorf, 1869). A professor at the University of Darmstadt, he shows that by observing the dependence of conductivity upon dilution he can determine the transfer velocities of the ions (charged atoms or molecules) in solution.
Dutch-born physical chemist Jacobus Henricus van't Hoff, 22, and French chemist Joseph-Achille Le Bel, 27, announce a concept that helps explain the property of optical rotation and will prove basic to the study of stereochemistry—the three-dimensional structure of organic compounds (see Wislicenus, 1873). Chemical formulas up to now have been written on paper in two dimensions, but Hoff and Le Bel note that carbon can comprise four different chemical compounds directed to the corners of a tetrahedron; these four different atoms are linked to a carbon atom, they exist in two forms, and the mirror images of these atoms or groups cannot be superimposed: either pair will be dissymetric and therefore optically active. It will later be found that all molecules are three-dimensional arrangements of atoms bonded to each other, that a carbon atom is often bonded to four other atoms (or groups of atoms) and that these other atoms are as far apart from each other as possible at the corners of a tetrahedron, with the carbon atom in the center. If two or more of the other atoms in a carbon molecule are the same, then the molecule is symmetrical—identical in all respects with its mirror image (simple molecules such as ethyl alcohol, carbon tetrachloride, and methane are symmetric); but many larger molecules, such as sugars, are asymmetrical, meaning that they have four different kinds of atoms, and their solutions are optically active, meaning that they rotate the plane of polarized light (as observed with a polarimeter or polariscope), their mirror images are not found in nature, but if they are synthesized from inorganic materials (or from organic materials that are not optically active), the result is a "racemic mixture"—a 50-50 mixture of right-handed and left-handed molecules (see Bijvoet, 1946).
Irish physicist George Johnstone Stoney, 48, uses knowledge gained from his studies of molecular physics and the kinetic theory of gases to estimate the number of molecules in a volume of gas under pressure. Having an erroneous idea of the number of atoms in a gram of hydrogen; his result is not correct, but his method is sound and he introduces the term electron for the fundamental unit of electricity (see Thomson, 1897).
German physicist Moritz H. Jacobi dies at St. Petersburg March 10 at age 72, having made significant contributions to the understanding of electricity; Physicist Anders J. Angstrom dies at Uppsala June 21 at age 59. He has been the first to use the 10-10 meter as a unit to measure wavelengths of light, and it will be named the angstrom in 1905.