Volumetric equipment

When solution must be pumped, consideration should be given to use of holding tanks between the dry feed system and feed pumps, and the solution water supply should be controlled to prevent excessive dilution. The dry feeders may be started and stopped by tank level probes. Variable-control metering pumps can then transfer the alum stock solution to the point of application without further dilution. Means should be provided for calibration of the chemical feeders. Volumetric feeders may be mounted on platform scales. Belt feeders should include a sample chute and box to catch samples for checking actual delivery with set delivery. Gravimetric feeders are usually furnished with totalizers only. Remote instrumentation is frequently used with gravimetric equipment, but seldom used with volumetric equipment. 

The estimation of the overall precision of a methodfrom its unit operations A frequent problem in analysis is the estimation of the overall precision of a method before it has been used or when insufficient data are available to carry out a statistical analysis. In these circumstances the known precision limits for the unit operations of the method (volume measurement, weighing, etc.) may be used to indicate its precision. Table 2.6 gives the normal precision limits for Grade A volumetric equipment. 

For other sources this experimental approach is not possible. E.g. for the purity of a material, the traeness of a balance or a volumetric equipment or similar uncertainties om knowledge is purely based on other information like certificates published by the manufacturer or a calibration laboratory. In some cases the only available information is the analyst s experi-... 

By their nature, gravimetric apparatus are quite fragile and care must be exercised in their use. Volumetric equipment usually contains fragile glass components. Continuous flow instruments are all metal, except for the sample cell, and are the least fragile of the various apparatus. 

Fig. 2.4. Arrangement of purge lines, (a) For the main box the lower manifold should be the inlet with a dense gas (for instance, Ar) and the outlet with a light gas (for instance, He). (b) A purge-gas manifold in the transfer port equipped with outlet jets to flush volumetric equipment.

In physics, the use of calibration hierarchies is well established and is used in any laboratory, e.g. for balances, volumetric equipment, spectrometer wavelengths, cuvette light path lengths, thermometers, barometers and clocks. 

Apparatus. The gas-handling and vacuum systems used were standard volumetric equipment (5). Liquid nitrogen was used as a constant temperature bath around the calorimeter and the pilot sample its temperature was checked by means of an oxygen vapor pressure thermometer. 

A matter of practical importance in nonaqueous titrimetry is that, when volumetric equipment is used, errors should be prevented that arise from solvent volatility and from characteristics of viscosity and surface tension that differ from those of water. Temperature coefficients of expansion are often about six times that of water, so careful control of temperature is needed when volumes are being measured. Gravimetric titration techniques are recommended, since they avoid most of these volumetric problems. Details of a gravimetric technique using a syringe have been given. ... 

Hydrogen adsorpiion measurements were made on the catalysts in conventional static volumetric equipment Hydrogen uptake was obtained from the isotherm plateau. Metal surface area was calculated assuming dissociative adsorption of hydrogen with one hydrogen atom on each surface nickel atom and assuming the cross-sectional area of nickel to be 0.065 nm. ... 

Uncertainty associated with the use of volumetric equipment at a temperature different from that of calibration, (7-Temp. 

Metal accessibility was determined by the H2-O2 titration method in a static volumetric equipment. Hydrogen preadsorbed at 500°C was titrated at 25°C by oxygen. Isotherms have been determined in the 0-50 torr range. Extrapolation to the original values was used to calculate the number of exposed atoms. 

Volumetric equipment should be used with solutions equilibrated to room temperature. Solutions diluted in volumetric flasks should be repeatedly mixed during dilution so that the contents are homogeneous before the solution is made up to final volume. Errors caused by expansion or contraction of liquids on mixing are thereby minimized. 

Volumetric equipment is marked by the manufacturer to indicate not only the manner of calibration (usually TD for to deliver or TC for to contain ) but also the temperature at which the calibration strictly applies. Pipets and burets are ordinarily calibrated to deliver specified volumes, whereas volumetric flasks are calibrated on a to-contain basis. 

Volume markings are blazed on clean volumetric equipment by the manufacturer. An equal degree of cleanliness is needed in the laboratory if these markings are to have their stated meanings. Only clean glass surfaces support a uniform film of liquid. Dirt or oil causes breaks in this film the presence of breaks is a certain indication of an unclean surface. 

The top surface of a liquid confined in a narrow tube exhibits a marked curvature, or meniscus. It is common practice to use the bottom of the meniscus as the point of reference in calibrating and using volumetric equipment. This minimum can be established more exactly by holding an opaque card or piece of paper behind the graduations (Figure 2-21). 

Microqalorimetry. Following a pretreatment at 623 K under vacuum (<10 torr) overnight, the differential heat of adsorption of ammonia was measured at 423 K using a SETARAM - Tian-Calvet type microcalorimeter associated with a volumetric equipment allowing the simultaneous determination of the adsorption isotherm. 

The performance of the titration can be controlled In a variety of ways (see Table 13.1) by use of empirical equations for the calculation of AV from preceding titration data points by use of microprocessors to control volumetric equipment (e.g. in photometric, potentlometrlc, coulometrlc titrations) or expand the scope of a given technique by use of robot stations In Implementing laborious manual methods or In handling toxic or hazardous substances etc. End-point detection Is usually based on E/A.V maxima and on first or second derivatives In the case of microprocessor- and microcomputer-controlled processes, respectively. Table 13.2 lists a chronological selection of calculation methods applied to titration curves [46]. 

The metal accesibiMty of the catalysts was determined by gas chemisorption (hydrogen, oxygen) at room temperature in a conventional volumetric equipment. The widely admitted adsorption stoichiometries are H/Pt = 0/Pt = 1. No chemisorption of hydrogen and oxygen on gold was observed at this conditions (14). The carvone hydrogenation reaction, in... 

Instrumental Errors. Instrumental errors are caused by nonideal instrument behavior, by faulty calibrations, or by use under inappropriate conditions. Typical sources of instrumental errors include drift in electronic circuits leakage in vacuum systems temperature effects on detectors currents induced in circuits from llO- power lines decreases in voltages of batteries with use and calibration errors in meters, weights, and volumetric equipment. 

Total metal dispersion- Dispersion was determined by chemisorption of oxygen in a static volumetric equipment (Micromeritics Accusorb 2100) with an attainable vacuum level of ca. 10-5 mm Hg. Degassing and Hj reduction were performed at 500 °C. The stoichiometry of oxygen to Pt and oxygen to Re was taken as one, independently that the metals were segregated, alloyed or sulfided (8). 

General principles for preparation of calibration solutions and matrix matched calibrators are described in Section 9.8.1 and similarly for QC samples in Section 9.8.2. Records to support the preparation, storage conditions (location and temperature) and use of these samples must be maintained at the analytical site, together with SOPs and information for all relevant apparatus including freezers and refrigerators, analytical balances, volumetric equipment etc. 

Volumetric procedures incorporate several important sources of systematic error. Chief amongst these are the drainage errors in the use of volumetric glassware, calibration errors in the glassware, and indicator errors. Perhaps the commonest error in routine volumetric analysis is to fail to allow enough time for a pipette to drain properly, or a meniscus level in a burette to stabilize. Pipette drainage errors have a systematic as well as a random effect the volume delivered is invariably less than it should be. The temperature at which an experiment is performed has two effects. Volumetric equipment is conventionally calibrated at 20°C, but the temperature in... 

Activated carbons and CMS were characterized by measuring the adsorption isotherms of N2 at 77 K and of CO2 at 298 K. A low temperature, N2 adsorption apparatus (Quantasorb, by Quantachrome) was used for the determination of N2 adsorption isotherms. CO2 adsorption data were obtained with a laboratory volumetric equipment. Surface areas were estimated from N2 isotherms by using the BET multiple point equation and from CO2 isotherms by using the Dubinin-Radushkevich equation. Prior to the measurement of N2 adsorption, samples were outgassed at 383 K for 12 hours under helium flow. For CO2 adsorption measurements, samples were first oven - dried at 383 K for 24 hours, and then outgassed overnight at 383 K, at a pressure of about 1 Pa. 

Some typical experimental setups for volume and density measurement are given in Fig. 6.3. Rarely is it possible to make a volume determination by finding the appropriate lengths. Almost always, the volume measurement will be based on a mass determination, as described in Chapter 7. For routine liquid volume measurement, common in the chemical laboratory, one uses volumetric equipment in the form of calibrated flasks, cylinders, burettes, and pipettes, as well as pycnometers. These instruments are usually calibrated for use at one temperature only. Their quality and use are described in many laboratory handbooks. Calibration is always done by weighing the instrument filled with water or mercury, or weighing the liquid delivered when the instrument is emptied. 

A modern adsorption microcalorimeter was built for the simultaneous measurement of isotherms and adsorption heats, establishing its correct functioning through adequate calibration of both the calorimeter part and the volumetric equipment of the adsorption part. For this purpose, the microcalorimeter calibration constant was found with values that go from 134.11 0.19 WV" to 156.67 0.23 WV. The adsorption isotherm was determined for a type NAZSM-5 zeolite as a reference solid to establish the correct functioning of the equipment. Micropore volume and superficial area were determined to be 0.20 cmVg and 296 m /g, respectively. These results agree very well with those obtained with commercial equipment. Finally, the differential heats of adsorption, for the same solid, were measured. The analysis of results gives valuable information about the studied C02/NaZSM-5 system, which is in concordance with other studies in the literature. 

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