Technikatörténeti szemle 19. (1992)

KÖNYVISMERTETÉS - Papers of the First „MINERALKONTOR” International Conference on the History of Chemistry and Chemical Industry (Veszprém, 12-16 August, 1991)

would be an outline of an absorption curve such as the typical one shown here (Figure 7). The photographic technique, while eliminating the inherent error of visual methods, still required considerable skill in manipulating the photometer and spectrograph, photographic processing, and interpretation of the results. However, it had the distinct advantage over the point-by-point method of both visual and early photoelectric spectrophotometers in that the entire spectrum was recorded on one plate, making it possible to observe spectrum details that might be otherwise overlooked in the manual wavelength adjustment and measurement of the other techniques. One American chemist who made significant contributions using photographic spectrophotometry was Wallace Reed Brode, who was born in 1900 and was a graduate student at Illinois when Arnold Beckman was a student there. After receiving his Ph. D. in 1925 Brode had a distinguished career at Ohio State University and at the Bureau of Standards. While at Ohio State, Brode and his students measured the absorption spectra of many compounds and made extensive correlations between spectra and molecular structure. His book «Chemical Spectroscopy" was initially published in 1939, with a second edition in 1943 (7). In addition to containing both a theoretical and practical introduction to spectroscopy, this text also contained a number of laboratory exercises designed to be used in a teaching environment. As a result it did much to popularize both emission and absorption spectroscopy. George R. Harrison, the MIT physicist who organized the famous summer spectroscopy conferences, also contributed significantly to the field in the 1920 to 1940 period. His book on ..Practical Spectroscopy" was first published in 1948 (5) and served as an important manual for those who were entering the field and needed to evaluate the available techniques for their own applications. It was the first manual to include the Beckman DU. Photoelectric spectrophotometry: New detection technology The photoelectric effect was first discovered in 1888, but it was not until 1900 that Philipp Lenard showed that electrons were ejected from irradiated metals, and that the rate of emission was proportional to the radiant power. In 1911 a German patent was granted to Wilhelm Berg for a photoelectric detector applied to a colorimeter. In the United States similar colorimeters were developed using a single voltaic cell, the Cenco Spectrophotelometer (Figure 8) shown here being typical. Early models used glass filters to isolate certain regions of the visible spectrum and a microammeter to read the output of the barrier-layer photovoltaic cell. By 1940 Coleman was marketing a two-unit double monochromator spectrophotometer, the second unit being a standard Coleman electron tube potientiometer to measure the output of the high-vacuum photocell. One of the more widely known spectrophotometers of the pre-DU days was developed by A. C. Hardy of MIT and manufactured by General Electric. It was the first commercial instrument to couple the detector reading to a recording device such that a continuous tracing of the absorption spectrum could be obtained. The Hardy instrument, however, costed more than S3000 in 1940, hardly putting it in the budget of many laboratories.