The Oesper Collections in the History of Chemistry, University of Cincinnati
Oesper Museum Booklets on the History of Chemical Apparatus
Like most museums, only about 25% of the holdings of the Oesper Collections in the History of Chemistry are on public display at a given time. In order to make the remaining 75% available in some form, it was decided to initiate a series of short museum booklets, each dedicated to a particular instrument or laboratory technique of historical importance to the science of chemistry. Each booklet would include not only photographs of both displayed and stored museum artifacts related to the subject at hand, but also a short discussion of the history of the instrument or technique and of its impact on the development of chemistry as a whole. Several of these booklets are expansions of short articles which have previously appeared in either the bimonthly series Museum Notes, which is posted on the Oesper website, or the series "Ask the Historian," which appeared in the Journal of Chemical Education between 2003 and 2012.
For more information please contact Editor/Curator: Dr. William B. Jensen, Oesper Professor of Chemical Education and History of Chemistry, University of Cincinnati.
The most recent five Oesper Museum Booklets are listed below. Please visit the UC Digital Resource Commons for the complete listing.
- Classical molecular weight determinations
Molecular weights were of no interest to chemists until the advent of John Dalton’s (figure 1) atomic theory in the first decade of the 19th century, when they became relevant in two distinct ways. The first of these has to do with the fact that calculation of a compound’s compositional formula using atomic weights and gravimetric composition gives information on only the relative number of each atom present, rather than the total number.1 Curiously this distinction does not appear to have been appreciated by Dalton.
- Electrolysis cells
The physical makeup of an electrolysis cell is virtually identical to that of the voltaic cell discussed in Booklet 8 of this series. Like the voltaic cell, it generally consists of two solid electrodes (called the cathode and anode) in contact with a suitable ionically conducting liquid or electrolyte and, in more elaborate cells, the cathode and anode may also be separated by a porous membrane or spacer. But if the physical construction is virtually identical, the chemistry is not. In a voltaic cell thermodynamically favorable chemical reactions are used to generate electrical energy, whereas in an electrolysis cell thermodynamically unfavorable chemical reactions are induced by means of an external source of electrical energy in the form of either a battery or a direct current (DC) electrical generator.
- Classic voltaic cells
A voltaic or galvanic cell is a device for the conversion of chemical energy into electrical energy.1 It generally consists of two solid electrodes (called the cathode and anode) in contact with a suitable ionically conducting liquid or electrolyte. In single-fluid cells the two electrodes share a common electrolyte, whereas in twofluid cells each electrode has its own chemically distinct electrolyte and these are separated from one another by means of a suitable membrane or porous spacer in order to minimize their rate of mutual mixing.
In late 1666 Sir Isaac Newton first performed his famous experiment demonstrating that white light was actually a mixture of seven basic colors: red, orange, yellow, green, blue, indigo, and violet (figure 1). This was done by passing a ray of white light through a glass prism and projecting the result on a white surface. On passage through the glass of the prism the light was refracted, which is to say, both its speed and direction of motion were altered. As we now know, the degree of refraction or the change in direction depends not only on the refractive index of the glass but also on the wavelength of the light itself, causing each color to emerge from the prism at slightly different angle and thereby resolving any mixture of wavelengths into its basic components (figure 2).
As indicated in the previous booklet in this series, the Oesper Apparatus Museum contains a large selection of visual colorimeters, filter photometers and spectrophotometers based on collections of these instruments donated in 1990 by the late Melvin Guy Mellon (figure 1) of Purdue University. Though additional instruments have subsequently been added, each of these collections has been named in Mellon’s honor in recognition of his initial gift. The M. G. Mellon colorimeter collection was the subject of booklet No. 4 in this series and his filter photometer collection the subject of booklet No. 5. The present booklet (No. 6) deals with his spectrophotometer collection.
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