Pure high precision

Abundances of lUPAC (the International Union of Pure and Applied Chemistry). Their most recent recommendations are tabulated on the inside front fly sheet. From this it is clear that there is still a wide variation in the reliability of the data. The most accurately quoted value is that for fluorine which is known to better than I part in 38 million the least accurate is for boron (1 part in 1500, i.e. 7 parts in [O ). Apart from boron all values are reliable to better than 5 parts in [O and the majority arc reliable to better than I part in 10. For some elements (such as boron) the rather large uncertainty arises not because of experimental error, since the use of mass-spcctrometric measurements has yielded results of very high precision, but because the natural variation in the relative abundance of the 2 isotopes °B and "B results in a range of values of at least 0.003 about the quoted value of 10.811. By contrast, there is no known variation in isotopic abundances for elements such as selenium and osmium, but calibrated mass-spcctrometric data are not available, and the existence of 6 and 7 stable isotopes respectively for these elements makes high precision difficult to obtain they are thus prime candidates for improvement. 

Total Nitrogen Content in "Pure" Explosives by High Precision FNAA... 

TNT and HMX were from highly purified laboratory samples and the nitrogen contents listed are calcd values for the pure compds. Precision and accuracy as indicated by the FNAA data for these compds are excellent and most likely represent the optimum that can be achieved by this technique... 

Under some conditions, it is difficult to incorporate an internal standard into a method. If the chromatogram is very complex, an internal standard may interfere with quantitation of a peak of interest. The development of highly precise sample transfer techniques, including modem autoinjectors, reduces the dependence of the experimentalist on the use of an internal standard to correct for effects of dilution and transfer losses. In many cases, external standardization can be used effectively. The weight percent purity is determined by comparing the area of each peak in a chromatogram with those generated by separately injected pure standards of known concentration. 

Theoretical results described above find applications in numerous high precision experiments with hydrogen, deuterium, helium, muonium, muonic hydrogen, etc. Detailed discussion of all experimental results in comparison with theory would require as much space as the purely theoretical discussion above. We will consider below only some applications of the theory, intended to serve as illustrations, their choice being necessarily somewhat subjective and incomplete (see also detailed discussion of phenomenology in the recent reviews [1, 2]). 

Salinity measurements are most often used in oceanography to determine seawater density. The conventional measure used by oceanographers for determining salinity is conductivity. This is feasible because the salt content of seawater is well defined, as is the temperature-related compressibility. As an alternative, the refractive index of water is a good descriptor of density when temperature is known or can be measured. Refractive index provides a high-precision method for determining the density of pure water. As various salts are added, the refractive index is a less exact predictor of density, although relative measurements can still be useful. 

Such a situation will often arise if the model does indeed fit the data well, and if the measurement process is highly precise. Recall that the F-test for lack of fit compares the variance due to lack of fit with the variance due to purely experimental uncertainty. The reference point of this comparison is the precision with which measurements can be made. Thus, although the lack of fit might be so small as to be of no practical importance, the F-test for lack of fit will show that it is statistically significant if the estimated variance due to purely experimental uncertainty is relatively very small. 

Determination of the amount of substance is thus in direct relation to basic units of the SI system and does not need a RM for comparison. The Faraday constant is one of the fundamental constants (it can be expressed as the product of the electron charge and the Avogadro constant). It enables the attainment of high precision and accuracy and is independent of the atomic weights of the elements in the sample. Its drawback is lower selectivity, a feature common to titration methods. This makes coulometry especially suitable for determination of relatively pure substances used as standards by other (relative) methods. The Faraday constant has been proposed as an ultimate standard in chemistry [3],... 

Benson and Krause (1976) have also published high-precision solubility data for 02, He, Ne, Kr, and Xe in pure water. Their data were fitted in terms of the Henry s law constant k in... 

The ability to perform the same analytical measurements to provide precise and accurate results is critical in analytical chemistry. The quality of the data can be determined by calculating the precision and accuracy of the data. Various bodies have attempted to define precision. One commonly cited definition is from the International Union of Pure and Applied Chemistry (IUPAC), which defines precision as relating to the variations between variates, i.e., the scatter between variates. [l] Accuracy can be defined as the ability of the measured results to match the true value for the data. From this point of view, the standard deviation is a measure of precision and the mean is a measure of the accuracy of the collected data. In an ideal situation, the data would have both high accuracy and precision (i.e., very close to the true value and with a very small spread). The four common scenarios that relate to accuracy and precision are illustrated in Figure 2.1. In many cases, it is not possible to obtain high precision and accuracy simultaneously, so common practice is to be more concerned with the precision of the data rather than the accuracy. Accuracy, or the lack of it, can be compensated in other ways, for example by using aliquots of a reference material, but low precision cannot be corrected once the data has been collected. 

We will review here experimental tests of quantum electrodynamics (QED) and relativistic bound-state formalism in the positron-electron (e+,e ) system, positronium (Ps). Ps is an attractive atom for such tests because it is purely leptonic (i.e. without the complicating effects of nuclear structure as in normal atoms), and because the e and e+ are antiparticles, and thus the unique effects of annihilation (decay into photons) on the real and imaginary (related to decay) energy levels of Ps can be tested to high precision. In addition, positronium constitutes an equal-mass, two-body system in which recoil effects are very important. 

In Eq. (17), the directly measured weights of the pycnometer— when empty, 1% when filled to the mark with pure water, and fEwhen filled to the mark with solution—are used. This equation is preferable to Eq. (16) for calculation of 4>, as it avoids the necessity of computing the densities to the high precision that would otherwise be necessary in obtaining the small difference d — c/g. 

The size of the kelvin, the SI temperature unit with symbol K, is defined by the statement that the triple point of pure water is exactly 273.16 K. The practical usefulness of the thermodynamic scale suffers from the lack of convenient instruments with which to measure absolute temperatures routinely to high precision. Absolute temperatures can be measured over a wide range with the helium-gas thermometer (appropriate corrections being made for gas imperfections), but the apparatus is much too complex and the procedure much too cumbersome to be practical for routine use. 

Most inorganic salts, when they melt, are found to flow and conduct electricity according to a simple Arrhenius law at all temperatures down to their melting points. For instance, unless measurements of high precision are used, the alkali halides appear to remain obedient to the Arrhenius equation even down to the deep eutectic temperatures of their mixtures with other salts. LiCl and KCl form a eutectic mixture with a freezing point of 351°C, some 300 K below either pure salt freezing point, yet the viscosity of the melt barely departs from Arrhenius behavior before freezing. 

The densities of the coins are very close to the density of pure copper, 8.92 g/cm . These measurements show that the coins are non-porous, and even the coins that apparently have lower densities may not be porous. Occasionally a coin that has a rough surface traps air at the surface, causing the weight of the coin in water to be less than it really is and thus decreasing the apparent density. The results in Table I also show that the densities of coins may be measured with high precision the average density is 8.92 0.03 g/cm (standard deviation = 0.03 g). 

The AC o polymers are resistant to oxidation in air and remain intact in solvents like toluene [11], This is in contrast to all other known alkali fullerides, including the fee high temperature AC o phases, which rapidly degrade in air. The air stability facilitates experimentation and the stability and the insolubility in solvents provides a mean for separating the polymer phase from other phases. Doping pure with precisely weighed amounts of alkalis at high temperatures is the usual synthesis of AQg compounds with A = K, Rb, Cs. The exact stoichiometry is hard to achieve and most early data are on mixtures of different phases. 

When compared with the other methods, the capillary rise method is the ultimate standard method in terms of the degree of theoretical exactitude, and, although it is the oldest method, it still gives the most precise liquid surface tension results if carefully applied, and when the time of measurement is allowed to be sufficiently long. However, with the improvement in computer-controlled electronic equipment, other methods now also have a very high precision. Some of the surface tension results are summarized in Table 6.1, and the interfacial tension between pure liquids in Table 6.2. 

A methanol model was previously implemented in the Cheetah code. The model is based on a combination of shock Hugoniot data and sound speeds determined via ISLS. High-pressure and temperature equation of state data on pure ethanol was not available, so Impulsive Stimulated Light Scattering measurements were made of the sound speed of ethanol at 250° C. Results are shown in Figure 5. A Cheetah exponential-6 potential model was fit to the ISLS measurements. The 3% difference between data sets shows the utility of Cheetah and the consistency between static and dynamic equation of state measurements. High precision ISLS measurements easily resolve ethanol velocities from 2-3% lower methanol velocities. 

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