Precision analytical balances

The two principal experimental apparatuses used to determine the density of a liquid are the pycnometer and the vibrating tube densimeter. The pycnometer method involves measuring the mass of a liquid in a vessel of known volume. The volume of the pycnometer, either at the temperature of measurement or at some reference temperature, is determined using a density standard, usually water or mercury. Using considerable care and a precision analytical balance accurate to 10 5 g, it is possible to achieve densities accurate to a few parts in 10s with a pycnometer having a volume of 25 cm3 to 50 cm3. 

What Lavoisier discovered is that there is no discernible change in mass during a chemical reaction. This means that if we carefully weigh all of the substances that are going to react with each other, and then carefully collect and weigh all of the products that form, within the limits of very precise analytical balances, there is neither an increase nor a decrease in mass. Mass is conserved. Lavoisier stated this as the law of conservation of mass. 

Then with the help of the precision micrometer, we determined the thicknesses of the obtained samples and their volumes were calculated using the known values of the thickness and diameter. The sample mass was measured by the precision analytical balance. The known sample volume and mass allowed us to find the density of the nanocomposite material. By this way it was possible to determine the dependencies of the material density on the molding temperature. These dependencies are presented in Figure 7.3 for the following samples pure modified low-density polyethylene (1), and nanocomposite materials based on low-density polyethylene matrix with 10% concentration of nanoparticles CdS (2) and MnO (3). 

WEIGHT.dat Thirty high-precision calibration measurements carried out on each of two analytical balances (LSD 0.01 mg) in the course of less than one hour using the calibration weight 30 g , cf. Ref. 25. 

Instrument/Equipment Effects Examples include the calibration and precision of an analytical balance, the specified tolerance for volumetric glassware and a temperature controller that maintains a mean temperature which is different (within specification) from its indicated value. 

The peak is cut from the original chart paper or from a photocopy and weighed on an analytical balance. This method is fairly precise and particularly useful for asymmetrical peaks but is subject to errors arising from variation in thickness and moisture content of the paper. 

If it is established that a measuring device provides a value for a known sample that is in agreement with the known value to within established limits of precision, that device is said to be calibrated. Thus, calibration refers to a procedure that checks the device to confirm that it provides the known value. An example is an analytical balance, as discussed above. Sometimes the device can be electronically adjusted to give the known value, such as in the case of a pH meter that is calibrated with solutions of known pH. However, calibration can also refer to the procedure by which the measurement value obtained on a device for a known sample becomes known. An example of this is a spectrophotometer, in which the absorbance values for known concentrations of solutions become known. We will encounter all of these calibration types in our studies. 

Any device routinely checked for calibration can be monitored in this way. For example, an analytical balance can be tested with a known weight, the value of the known weight being the desirable value and the expected range of precision dictating the warning and action limits (Experiment 1). 

By dilution measure out 6.22 mL of the 4.021 M solution as precisely as possible (measuring pipet), dilute it to 100.0 mL (volumetric flask), and shake. By weight of the pure solid weigh out 2.650 g on an analytical balance, place in a 100-mL volumetric flask, dissolve in water, dilute to 100.0 mL, and shake. 

As we have seen that the volumetric analysis essentially requires the precise and accurate measurement of weights and volumes of interacting solutions. However, the weights are measured upto the fourth place of decimal by using a manually operated good analytical balance or a single-pan electrical balance that need to be calibrated periodically with the help of a standard weight box. 

Laboratory mill (e.g., UDY Cyclone Sample Mill) equipped with 250-p.m screen Analytical balance with 0.1 mg precision Leak-proof centrifuge tubes with caps (see recipe)... 

The filters were weigthed before and after sampling with an automated analytical balance in a controlled environment. In general, the precision of the measurement of the mass was 0.0001 g and the average reproducibility 0.003 g. 

Gravimetric methods are based on the quantitative measurement of an analyte by weighing a pure and insoluble compound from the analyte. Analytical balances, which provide accurate and precise data, are used for this purpose. Detailed information on gravimetric methods and their applications can be found in the literature.3... 

Analytical balances are those of Class I and Class II (see Table 2.21) and require a division of the scale s capacity that is typically smaller than 10 5 of the total capacity with a readability of 0.1 ig to 0.1 mg (10 7 to 10-4 g). Analytical balances have the greatest precision for the most demanding work. For many years, only a properlymade two-pan balance could achieve the precision required to obtain the required level of accuracy. Despite their accuracy, weighings made on two-pan balances were slow and inefficient. Eventually, technology improvements in single-pan balances brought them to meet and eventually exceed the capabilities of two-pan balances, yet maintain their speed and efficiency. 

Force-Coil Analytical Balances. The most precise modern analytical balances use a "force coil," mounted in a magnetic field the current needed to counterbalance the weight placed is measured (electromagnetic force restoration balance) or an optical system measures displacement these can be sensitive to 1 part in 3 x 106. Some "window comparators" yield a precision of 1 part in 109. 

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