Lead oxidation work may lead to standards
than of the state of an oxide formed. I The most recent work at Rutgers on pyrophoric cobalt, nickel, and tin gives results which confirm this com parability, Dr. Toby says.
Pyrophoric (spontaneously igniting) lead reacts with oxygen over a wide range of temperature and pressure at close to 100% efficiency [/. Phys. Chem., 70, 1478 (1966)]. And the reaction is fast. For example, the lead-carbon mixture removes 50% of available oxygen in a reaction cham ber in less than 30 seconds. This sug gests that the highly reactive material may be useful in removing oxygen from streams of other gases. An even more basic benefit may be that stand ard rate constants may be obtained for oxidation reactions of many metals. These conclusions have emerged from undergraduate research at Rut gers University, New Brunswick, N.J., by chemistry seniors Joseph Charles (now at Lever Brothers, Edgewater, N.J.) and Peter W. Kopf under Dr. Sidney Toby. The Rutgers trio quan titatively measured the chemical com position and reactivity of the combus tible lead. Prepared from lead citrate decomposed in a vacuum between 300° and 600° C , the material con tains 83.5 ± 1% (by weight) lead. The remainder is carbon. The lead's pyrophoricity holds in samples prepared well above the melt ing point of lead (327° C ) , the re search team notes. Furthermore, the volume percentage of carbon in the lead mixture may be as high as 90%. Therefore the lead seems to be ad sorbed on a carbon matrix in finely di vided form. Thus dispersed, the metal is prevented from coalescing. The lead's dispersal is the key to its reaction rate with oxygen, the team found. Dispersal eliminates the us ual oxidation complexities caused by diffusion of oxygen through films of metal oxide. In the Rutgers experi ments, the reaction is first-order in an
Scientists are beginning to apply elec tron probe microanalysis to the detec tion and determination of a wide vari ety of substances in biological mate rials. The technique shows potential as a useful analytical tool when ap plied in diverse studies such as these: • The role of zinc in the reproduc tive systems of mammals. • Composition of animal cell com ponents. • Mechanisms of plant growth. Dr. Louis Zeitz of Sloan-Kettering Institute, New York City, and C. A. Anderson of Hasler Research Center, Goleta, Calif., have used the electron probe microanalyzer as an analytical aid to a study of zinc's role in the re productive system of mammals. With the technique, they have found that zinc is distributed in a nonuniform manner in lateral and dorsal lobes of the rat's prostate gland, Dr. Zeitz told scientists at the First National Confer ence on Electron Probe Microanalysis held at the University of Maryland. The electron probe microanalyzer can be used to detect certain enzymes and mucopolysaccharides in human and animal cells. Dr. A. J. Tousimis and Jon C. Hagerty of Biodynamics Research Corp., Rockville, Md., have combined histochemical methods with electron probe microanalysis to deter mine the distribution of alkaline and acid phosphatases, adenosine triphos phatase, and acid mucopolysaccha rides in animal tissue sections. Electron probe microanalysis is also
initial pressure range of 0.02 to 2 torr
being used as an aid in determining
and a temperature range from —115°
growth m e c h a n i s m s
to + 7 5 ° C. Gravimetric, ESR, and BET specific surface testing show that the carbon takes no part in the reac tion. The activation energy is low (2.9 ± 0.2 kilocalories per mole compared to 43 kilocalories per mole for massive lead). The barrier to re action (in the Arrhenius equation) is predominantly the entropy rather than the enthalpy of activation. Such clear-cut parameter determi nations with lead prompt Dr. Toby to suggest a standard means of compar ing metal oxidation characteristics. He foresees that many other metals, if studied in finely divided form, would yield similar oxidation parameters. All of these constants would be di rectly comparable, since they are func tions of the metals themselves rather
Electron probe used on biological tissue
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plants. For example, Dr. A. L. Kenworthy of Michigan State University (East Lansing)
GENERAL ANILINE & FILM CORPORATION
and H. T. Dryer of
Applied Research Laboratories, Dear born, Mich., have used the technique to determine the distribution of potas sium in the leaves of grape plants. Tooth decay. The electron probe microanalyzer is useful in studying the effects of certain minerals on tooth decay. In this study, Dr. A. J. Saffir and Dr. R. E. Ogilvie of Massachu setts Institute of Technology use an instrument that utilizes x-ray absorp tion rather than x-ray emission spec troscopy. The MIT scientists have found that the technique can show lo cations in certain portions of rats' teeth in which there is decreased formation of minerals such as phosphate. |
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