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)

ric Spectrophotometer" that chemists later would often, and sometimes with affection and reverence, call simply „the DU." The first advertisement for the Beckman Spectrophotometer appeared two months after the MTT conference (Figure 3), and within a year seventy-two of the instruments had been sold. More meaningful, however, was the emergence of scientific papers utilizing this new device for spectral measurements, which began exactly one year after National Technical Laboratories announced the DU's availability. For instance Kenneth Morgareidge of the Nopco Vitamin Laboratories in 1942 stated that the Beckman quartz photoelectric spectrophotometer was used to obtain the reported experimental data (3). It was a perfect marriage, for chemists had an increasing need to measure spectra, and the Beckman DU was the instrument to do it, featuring a relatively low cost, ease of operation, and accessibility to the crucial ultraviolet region that was previously not within reach of many research and analytical laboratories. But what was life like before the DU? Colorimetry: The beginning of optical chemical analysis The ancient Greeks and Romans determined the presence of alkali in natural waters by the decoloration of red wine. In 60 A. D. Pliny the Elder used an extract of gallnuts to test for the presence of iron in vinegar. These simple tests are examples of colorimetry, a method of analysis based on a change in color due to a chemical reaction. By the mid-nineteenth century it was recognized that the production of a color by the addition of a test reagent to an unknown sample solution could also be applied as a quantitative measurement, since the intensity of the color is proportional to the concentration. Progress was slow throughout the remainder of the nineteenth century as the search continued for appropriate chemical reactions that gave a unique color with a specific substance. Requirements for a reliable colorimetric analysis include reagent and color stability, an intense color that forms rapidly and corresponds to the visual region where the eye is sensitive, and conformity to Beer's Law to validate the calculation of concentration. Concurrently, methods were devised for ..measuring" color by comparing the test solution with a standard solution. By the 1920s, when John Yoe of the University of Virginia published his book on colorimetry (4), the scientific literature was filled with many themes and variations that evolved to meet the demand for increased accuracy as analysts applied colorimetry to an intensifying variety of practical problems of industrial and commercial value. The most direct method was to compare the sample to a series of standard solutions with varying known concentration. A ..simple" matching of colors gave a direct reading of concentration without any calculations. A rack for holding the standard tubes was offered as early as 1889 by the J. H. Berge Company, using a mirror to reflect light up through the adjacent tubes. In this device used for sugar analysis, a rack containing unknowns could be moved in front of the standard tubes until the visual equality of color was made. The basic design remained unchanged for half a century, although more elaborate devices were developed. Thus a roulette wheel was used for pH measurements where color comparisons had been refined to a high degree of refinement in color variation