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From Caveman to Chemist Circumstances and Achievements
W
hat was the connection between early chemistry and magic? What was the logic that made alchemists think they could make gold out of lead? Why were gases not recognized until the 17th century? Why did it take 49 years before Avogadro's hypothesis was accepted? In From Caveman to Chemist, author Hugh Salzberg traces the oddities of chem istry, examining cultural and political influ ences on the ideas of chemists. He follows the evolution of chemistry from the Stone Age beginnings of ceramics and metallurgy, through the rise and decline of alchemy, to the culmination of classical chemistry in the late 19th century. Chapters 1 through 9 lead from prehistoric technology, through ancient and medieval science to the study of chemicals and reactions that resulted in the 16th century birth of scientific chemistry. Subsequent chapters focus on key chemists such as Sala. Boyle. Black. Lavoisier. Dalton. Berzelius. Laurent, and Arrhenius as they developed the ideas that led to classical chemistry and the concepts of molecules, chemical reactions, homology, valence, and molecular formulas and structures, among others. Twenty topical illustrations enhance the text. Six timelines and two maps help readers understand the influences of early history on chemistry. Hugh W. Salzberg 300 pages(1991) Clothbound: ISBN 0-8412-1786-6 Paperbound: ISBN 0-8412-1787-4 $24.95 $14.95 Order from: American Chemical Society, Distribution Office, Dept. 88 1155 Sixteenth St., N.W., Washington, DC 20036
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1122 A · ANALYTICAL CHEMISTRY, VOL. 64, NO. 23, DECEMBER 1, 1992
INSTRUMENTATION by dating techniques. An almost non destructive method of microsampling can be used to obtain pigment sam ples. A dry cotton-wool bud is used to rub ~ 10 μg of pigment from the p a i n t i n g . The cotton-wool bud is then wiped on a quartz glass sub strate, and the material is analyzed by TXRF (Figure 9). Even such a small amount of sample is sufficient to identify the respective pigment by key elements. S u r f a c e a n a l y s i s . Despite the fact that TXRF is basically a surfacesensitive method, it was not used im mediately for genuine surface analy sis. The first application in this field was the determination of metallic impurities in and on the oxide layer of silicon wafers (29). For this task, TXRF is the most sensitive technique in use today for element-specific con tamination control (30). T h e c h a r a c t e r i z a t i o n of n e a r surface layers has t a k e n even greater advantage of the standingwave phenomenon. Layer thickness, density, and element composition have been determined as a function of the depth normal to the interfaces (5, 8, 20), and TXRF is the only spec trometry method by which the den sity of surface layers can be deter mined directly. This capability can be illustrated by the Pd alloy system considered previously as an example for the standing-wave pattern inside a lay ered structure. Figure 10 shows the measured fluorescence intensities of Cr, Fe, Ni, and Pd originating from the two layers, and of Si originating from the substrate, as a function of the incident angle. The solid curves represent angular dependencies ob tained through an iterative fitting procedure. The calculations use only instrumental calibration factors from p u r e e l e m e n t s t a n d a r d s . Beyond that, they are exclusively based on the Fresnel relations. For t h i s t w o - l a y e r system, t h e thickness, composition, and density of each layer were determined (5). The implementation of an appropri ate wavelength-dispersive or β de tector (31) or t h e combination of s p u t t e r i n g techniques with TXRF may result in further progress. The determination of light elements, and of the chemical state as well as lat eral and depth profiling with high resolution, are challenging tasks for the near future.
References (1) Yoneda, Y.; Horiuchi, T. Rev. Sci. Instrum. 1971, 42, 1069-70. (2) Aiginger, H.; Wobrauschek, P. Nucl.
