Weight of a measurement

It is conventional to define (for the case being considered) the weight of a measurement yi to be inversely proportional to the variance of y that is. 

As these conversion equations show, in addition to the molecular weight of a measured gaseous pollutant, the temperature and pressure at the time of the measurement must be known. Because this information is often not given in the literature, no attempt has been made in this report to convert to a common unit. 

The density of fats and oils is an index of the weight of a measured volume of the material. This property is important not only for designing of equipment but also for the estimation of the solid fat index (SFI). The SFI is related, approximately, to the percentage of solids in a fat at a given temperature. When determined at a number of specified temperatures, it can be especially useful to margarine manufacturers or other processors who need to control the characteristics of their manufactured products by blending. 

The more precisely a measurement is made, the smaller is the e.s.d. of that measurement and the larger the weight or confidence that should be assigned to it. As a first approximation, the weight of a measurement can be taken as the reciprocal of the square of its e.s.d. Another type of weighting function also takes systematic errors, such as instrumental errors, into account by use of a small constant fc. 

Weight of a measurement A number assigned to express the relative precision of each measurement. In least-squares refinement the weight should be proportional to the reciprocal of the square of the estimated standard deviation of the measurement. Other weighting schemes frequently are used. 

There are alternative but related means of expressing the weight of a measured volume of a product. 

Once the value of the constant and the a value in Eq. (2.36) have been evaluated for a particular system, viscosity measurements constitute a relatively easy method for determining the molecular weight of a polymer. Criticize or defend the following proposition Since viscosity is so highly dependent on molecular weight for M > M, a 10% error in 17 will result in a 34% error in M above M, but only a 10% error in M below M, . 

An important application of Eq. (3.39) is the evaluation of M, . Flory et al.t measured the tensile force required for 100% elongation of synthetic rubber with variable crosslinking at 25°C. The molecular weight of the un-cross-linked polymer was 225,000, its density was 0.92 g cm , and the average molecular weight of a repeat unit was 68. Use Eq. (3.39) to estimate M. for each of the following samples and compare the calculated value with that obtained from the known fraction of repeat units cross-linked ... 

Experiments based on the Poiseuille equation make intrinsic viscosity an easily measured parameter to characterize a polymer. In the next section we consider how this property can be related to the molecular weight of a polymer. 

Thus we have finally established how light scattering can be used to measure the molecular weight of a solute. The concentration dependence of r enters Eq. (10.54) through an expression for osmotic pressure, and this surprising connection deserves some additional comments ... 

The second parameter, tear strength, describes the film resistance to tear propagation. It is measured with a special apparatus, the Ehnendorf Tear Tester (ASTM D1922), and defined as the weight of a loaded pendulum capable of tearing a notched piece of film. Two values are usually measured for each film sample. One determines tear propagation in the machine direction of the film, the other in the transverse direction. 

Specific gravityis the ratio of the weight of a given volume of oil to the weight of the same volume of water at a standard temperature, usually 60°F (15.6°C). This method of measuring density and gravity first arose as a result of the need to define the character of products in more detail it was natural to extend the measure to cmde oils in general. 

Production and consumption of wood products and residues are measured ia various units, based on common usage and their metric equivalents (2—4). Pulpwood logs and fuelwood are commonly measured ia cords. A cord refers to a stacked pile of wood, with outside dimensions of 4 by 4 by 8 ft (1.22 by 1.22 by 2.44 m) and a volume of 128 ft (3.62 m ). The weight of a cord depends on density of wood and bark and on moisture content. In the United States, it can range from 1.3 to 1.7 short tons (1.2 to 1.5 metric tons), air dried. 

It is seen that the molecular weight of a solute having a density between 0.85 and 1.25 can be estimated experimentally from peak width measurements for 90% of the compounds within an error of 13% (80% of the samples gave an error of less than 10%). Again, depending on the field of application, it should be noted that such data for a given substance can be obtained in addition to its separation from... 

Mg/L Milligrams per liter = ppm (parts per million) - expresses a measure of the concentration by weight of a substance per unit volume. 

In physics, the word specific implies a ratio. Weight is the measure of the earth s attraction for a body, which is called gravity. Thus, the ratio of the weight of a unit volume of some substance to the weight of an equal volume of a standard substance, measured under standard pressure and temperature, is called specific gravity. The terms specific weight and specific density are also sometimes used to express this ratio. 

The °AP1 gravity measures the density of a hydrocarbon liquid. Specific gravity (SG) is another common measurement of density. The liquid SG is the relative weight of a volume of sample to the weight of the same volume of water at 60°F (15.5°C). 

Suppose such a vapor-density measurement shows that a given volume of ethanol at 100°C and one atmosphere weighs 1.5 times as much as the same volume of oxygen gas at 100°C and one atmosphere. Since equal volumes contain equal numbers of molecules at the same temperature and pressure (Avogadro s Hypothesis), one molecule of the unknown gas must weigh 1.5 times the weight of a molecule of 02. Therefore,... 

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