Experimentation techniques and apparatus

Reference Books. The two series of books listed below describe important experimental techniques and apparatus for a variety of physical measurements. These books also deal with the phenomenological theory of the methods described. 

The experimental techniques and apparatus have been described in detail elsewhere. (8, 9) Titania and niobia were deposited onto the clean metal foils by vaporizing either a Ti-Ta alloy wire or a niobium wire in 10-7 Torr H2 at 800K. Auger electron spectroscopy (AES) was used to determine the oxide coverages, and temperature programmed desorption (TPD) was used to determine the effect of the oxide layers on the adsorption of CO and H2. Methanation rates were measured in a side chamber which allowed the sample to be characterized by AES before and after rates were measured. All rates were measured with 100 Torr CO and 400 Torr H2, and conversion to methane was always kept less than 1%. 

New experimental techniques and apparatus for studying population interactions need to be developed. Alternate and improved methods of obtaining census data on systems containing two or more populations are critical needs, and improved, automated means of making chemical analyses of abiotic media would be most helpful, too. 

Varella, Evangelia A. Experimental techniques and laboratory apparatus in ancient Greece drug and perfume preparation. Medicinanei secoli 8, no. 2 (1996) 191-206. 

These and other factors must b6 examined before a method or apparatus is condemned for lack of agreement with some other method or instrument. It is often simpler and more definitive to establish that an apparatus is properly working and calibrated than it is to use reference standards which are subject to the hazards listed above. Furthermore, the question must always arise regarding the merits of the technique and apparatus used to establish the value of the standard in the first instance. Experimental results obtained with a carefully calibrated apparatus are preferred to results which may agree with a presumed standard whose properties may change or which may have been incorrectly measured in another laboratory. 

An entire book in itself would be necessary to fully explore the many different surface science experimentation techniques used within the research community, thus making this section merely a brief overview. The reader is encouraged to read the referenced literature for more in-depth information on the techniques and apparatuses used for particular measurements or investigations [17, 21-23]. 

ENDOR (Electron Nuclear Double Resonance) involves the simultaneous application of a microwave and a radio frequency signal to the sample. This is a technique invented by Feher in 1956. The original studies were on phosphorous-doped silicon. A description of the experimental results and apparatus used is presented in two Physical Review articles [24, 25], An excellent treatment of EPR double resonance techniques and theory is given in the book by Kevan and Kispert [26], What follows here is the theory and application of ENDOR used the in analysis of single crystal data with the goal of identifying free radical products in DNA constituents. 

Even when for all these techniques the Fourier transform is essential, the experimental techniques and thus the apparatus are completely different. A famous general monograph on Fourier transform techniques has been compiled by Bracewell, one of the pioneers [12],... 

In his retirement. Sand wrote "Electrochemistry and Electrochemical Analysis." This appeared in three slender volumes during the War years (Tl) Voliame II, which carries the subtitle "Gravimetric Electrolytic Analysis and Electrolytic Marsh Tests," surveys apparatus and experimental techniques and gives concise instructions for the performance of numerous analyses. It acknowledges Sand s earlier contribution to L inge and Keane s encyclopedic work (72). 

In this chapter we introduce the basic experimental techniques and associated glassware and apparatus that are commonly used in the organic chemistry laboratory. In some Instances, only the practical aspects of a particular technique are discussed in this chapter, and the theoretical principles underlying it are presented in later chapters. 

It soon became apparent that there were two types of students with different needs. One group had almost no experience in infrared spectroscopy and wanted fundamental information on apparatus, experimental techniques, and applications. The second group had substantial laboratory experience in infrared spectroscopy and wanted much more emphasis on the interpretation of spectra. Therefore, starting with the third year (1952), two separate courses were given in successive weeks. The first was devoted to experimental aspects. In addition to morning lectures, each smdent had 10 hours of laboratory in the afternoons (2 hours per day for five days). The second course concentrated on the theory and applications of infrared spectra with heavy emphasis on characteristic group frequencies. An important feature was 10 hours devoted to solving problems in the interpretation of unknown spectra. 

Experimental techniques based on the application of mechanical forces to single molecules in small assemblies have been applied to study the binding properties of biomolecules and their response to external mechanical manipulations. Among such techniques are atomic force microscopy (AFM), optical tweezers, biomembrane force probe, and surface force apparatus experiments (Binning et al., 1986 Block and Svoboda, 1994 Evans et ah, 1995 Israelachvili, 1992). These techniques have inspired us and others (see also the chapters by Eichinger et al. and by Hermans et al. in this volume) to adopt a similar approach for the study of biomolecules by means of computer simulations. 

Smeatnii s elegant experimental technique enabled him to deal with both hydraulic and mechanical friction losses, allowing him to calculate water velocity at the wheel and thereby determine an effective nr virtual head. Smeaton s experimental apparatus was a brilliant device that enabled him to measure the efficiency of the wateiwheel, alone rather than the overall efficiency of the experiment. Smeaton was able to conclusively shov that a water-wheel when driven by the weight of water alone, is about twice as efficient as when driven by the impulse of water. This demonstration ensured that British mills, wherever possible, from then on would be fitted with overshot or breastshot wateiwheels, rather than undershot. 

The activity of a volatile solvent in a solution that contains a nonvolatile solute can be obtained from an experimental technique known as the isopiestic method .19 An apparatus is constructed similar to that shown in Figure 6.17. The mixture in container A is a solution of a nonvolatile solute in a solvent in which A], the activity of the solvent, has been accurately determined in other experiments as a function of concentration. Containers B and C hold solutions of other nonvolatile solutes in the same solvent. These are the solutions for which the activity of the solvent is to be determined. 

Our experimental techniques have been described extensively in earlier papers (2, 13). The gamma ray irradiations were carried out in a 50,000-curie source located at the bottom of a pool. The photoionization experiments were carried out by krypton and argon resonance lamps of high purity. The krypton resonance lamp was provided with a CaF2 window which transmits only the 1236 A. (10 e.v.) line while the radiation from the argon resonance lamp passed through a thin ( 0.3 mm.) LiF window. In the latter case, the resonance lines at 1067 and 1048 A. are transmitted. The intensity of 1048-A. line was about 75% of that of the 1067-A. line. The number of ions produced in both the radiolysis and photoionization experiments was determined by measuring the saturation current across two electrodes. In the radiolysis, the outer wall of a cylindrical stainless steel reaction vessel served as a cathode while a centrally located rod was used as anode. The photoionization apparatus was provided with two parallel plate nickel electrodes which were located at equal distances from the window of the resonance lamp. 

Apparatus and Procedure. The apparatus and procedure were identical to those outlined in ref. Surface composition measurements were based on an O2-CO titration technique described by Miura and Gonzalez (5-6). The ratio of surface metal/02/CO was 1/1/T on Ru-sllica, 1/0.5/1.75 on Rh-sllica, 1/0.5/2.0 on Pt-silica and 1/0.5/1.6 on Ir-silica. These titration ratios were found to be independent of surface composition. Surface compositions determined by the O2-CO titration method have been verified using a variety of experimental techniques (2,5-6). 

The pH-metric technique used to determine partition coefficients was first used in the 1950s in solvent extraction of metal complexes [280-282], but it is in pharmaceutical research that it is most widely used thanks to the recent development of a fully automated and computer-controlled apparatus [125,283]. The potentiometric approach has been validated in various solvent systems [284-287], and it has become a relevant and expanding experimental technique to obtain lipophilicity descriptors [257,287-289]. 

An unusually extensive battery of experimental techniques was brought to bear on these comparisons of enantiomers with their racemic mixtures and of diastereomers with each other. A very sensitive Langmuir trough was constructed for the project, with temperature control from 15 to 40°C. In addition to the familiar force/area isotherms, which were used to compare all systems, measurements of surface potentials, surface shear viscosities, and dynamic suface tensions (for hysteresis only) were made on several systems with specially designed apparatus. Several microscopic techniques, epi-fluorescence optical microscopy, scanning tunneling microscopy, and electron microscopy, were applied to films of stearoylserine methyl ester, the most extensively investigated surfactant. 

Systems which might be of interest for molecular solvation, and which have been investigated by various techniques are indicated in Table 7. Gas-phase hydration enthalpies for the ions Pb+ X58) and Bi+ 159> are also given in Table 7. In their studies, Tang and Castleman iss.is ) used an apparatus similar to that used by Kebarle and co-workers. Tantalizing as the existence of data for these ions might be for quantum chemists, who would prefer to know more about small ions like Be++, it allows nevertheless the optimistic conclusion that a remarkable increase of activities in the field of gas-phase solvation can be expected in the near future. One should bear in mind that the experimental techniques were introduced only a few years ago. Probably very soon theoreticians will have at their disposal experimented reference data for a lot of interesting systems. 

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