Humboldt State University
Robert A. Paselk Scientific Instrument Museum
Beckmann Differential Thermometer
Central Scientific Co.
Humboldt State College, <1940?
The Beckmann thermometer was invented by Ernest Otto Beckmann (1853-1923), also noted for the Beckmann transformation in organic chemistry, as a result of his work with oximes. His interest in the physical properties of these molecules lead him to invent a number of ingenious apparatus for measuring colligative properties based on the theoretical work of Francois Marie Raoult (1830-1901). He began publishing this work around 1888. Beckmann developed the differential thermometer bearing his name, which could accurately measure temperatures to about 0.001° C, in order to measure the very small temperature changes found in boiling point and freezing point determinations of molecular weight.
The thermometer is a Cenco model No. 19410 (made in Germany). It is 57.5 cm in overall length, with a 35.5 cm long milk glass baking inside the large tube. There is a nickel cap on top made of straight tubing to which a flat, knurled-edge top with a small turned knob in the center is soldered. The thermometer is graduated from -0.1 to 6.1 °C by 1/100 °C on the main scale, and from -9 to 144 °C by single degrees on the upper "setting" scale. The upper scale has every 10 degrees numbered (obviously by hand), while the main scale is numbered every 0.2° with larger numbering at each degree.
Research: The metal cap appears to be of an early style, not shown in the listings for 1976, 1960 (J-300, pg 257), 1950 (J-150, pg 367), or 1941 (J-141, pg 380) Cenco catalogs, even though the same model number is used (19410). A similar cap style does show up in the 1927 (C-227) Cenco catalog (p 664), but it is given a different catalog number (13522)
Gascoigne, Robert Mortimer. A Chronology of the History of Science, 1450-1900. Garland Publishing, Inc. New York (1987) pg. 137
Gienapp, Ruth Ann. "Beckmann, Ernest Otto" in Dictionary of Scientific Biography, vol. 1 (Charles Coulston Gillispie, editor), Charles Scribner's Sons. New York (1970) pg. 553.
Laidler, Keith J. The World of Physical Chemistry. Oxford Univ. Press. Oxford (1993) pg. 124.
© R. Paselk