Pycnometers, density measurements

Research and development technologists at the Dow Chemical Company can characterize materials in a variety of ways. One material property that is especially critical in polymer foaming and processing technology is density. A tool used for measuring the density of a material is called a pycnometer. There are many different manual and automatic types to choose from. For extremely accurate and precise density measurements, an easy-to-use, fully automatic gas displacement pycnometer is utilized. Analyses are commenced with a single keystroke. Once an analysis is initiated, data are collected, calculations performed, and results displayed without further operator intervention. 

Dow technologist Kenn Bouchard utilizes an automatic gas displacement pycnometer for measuring density in materials characterization. 

Other Measurements. Particle size distributions were measured by the Coulter Counter method. Absolute density measurements were made using the well known pycnometer method. 

Equilibrium vapor condensate was analyzed by means of density measurement at 25.00° 0.02°C. An Ostwald pycnometer (capacity ca. 5 cm3) was used. Liquid phase composition was calculated by taking a material balance. In this case, the three moles of water present in trihydrous lithium perchlorate were considered water component. The accuracies of both compositions were 0.001 mole fraction. 

The densities of the solvent and of / -lactoglobulin A ( -Lg) in 40% (v/v) 2-chloroethanol, in the presence of 0.01 M HC1 and 0.02M NaCl, were determined, with and without prior dialysis, in a 10-ml pycnometer at 20°C. Solutions were prepared as described previously (8, 24). The solutions were filtered through millipore filters in syringe adapters just before the density measurements. Protein concentrations were determined after filtration by ultraviolet absorption at 278 nm. The apparent partial specific volume, oapp, was calculated from the densities using the standard equation (21, 25) ... 

The densities of sea water, normal, diluted, and concentrated, and of aqueous solutions of ammonium bicarbonate are given as a function of concentration in Figure 5. Figure 6 gives the densities of solutions of ammonium bicarbonate made up in sea water of varying salinity. All of these density measurements were made at 20° C. by means of a pycnometer. 

A large volume expansion for solutions of sodium in ammonia was first reported by Kraus and Lucasse (17). Since this initial report, many investigations have been made of the volume expansion for a number of alkali metal-ammonia solutions. The techniques employed in these investigations have varied from density measurements for concentrated solutions using the Westphal Balance or Pycnometer to dilatometric studies for dilute solutions, which measure the volume expansion directly. 

Methods of measurement of coal density include use of a gas pycnometer and particle density by mercury porosimetry. However, the difference in density values using different gases must be recognized since, for example, density values measured by nitrogen may be greater than those obtained when helium is used. Density measurement depends on adsorption of gas molecules, and differences (between nitrogen and helium) may be due to nitrogen adsorption on the coal surface. 

Density measurements were carried out by the use of an air comparison pycnometer and the specific surface area was determined on milled and unmilled sample using a Stroklein areameter. The data are sunmarized in Table 7. 

The skeletal density, also called the true density, is defined as the density of a single particle excluding the pores. That is, it is the density of the skeleton of the particle if the particle is porous. For nonporous materials, skeletal and particle densities are equivalent. For porous particles, skeletal densities are higher than the particle density. Measurements of the skeletal density can be made by liquid or gas pycnometers. 

In this experiment the partial molar volumes of sodium chloride solutions will be calculated as a function of concentration from densities measured with a pycnometer. 

It was necessary to measure the dielectric constant and density of each solvent mixture studied. Densities were determined in a constant-temperature bath maintained to within 0.02°C. Gay-Lussac pycnometers with a capacity of 25 mL were used for density measurements. Dielectric constants were determined with a Balsbaugh Model 2TN50 conductivity cell having a cell constant of 0.001. A Janz-Mclntyre a-c bridge (17) was used. The dielectric constants and densities of the solvents are listed in Table I, along with the constants A and B of the Debye-Hiickel theory. 

Density (ASTM D-1298, IP 160) is an important property of petroleum products because petroleum and especially petroleum products are usually bought and sold on that basis or, if on a volume basis, then converted to mass basis via density measurements. This property is almost synonymously termed as density, relative density, gravity, and specific gravity, all terms related to each other. Usually a hydrometer, pycnometer, or more modem digital density meter is used for the determination of density or specific gravity (ASTM 2000 Speight, 2001). 

In order to carry out the density measurements in a wide range of temperatures, a suitable glass pycnometer was used the pycnometer capillary is placed laterally with respect to the chamber containing the sample and the filling liquid, and is provided with an upper (expansion) and a lower (contraction) spherical cavity. A low molecular weight silicon oil (Dow Corning 200/20) was used as the filling liquid. 

DV Cure. Shrinkage upon UV Cure was determined for AH 8, AM 9, and the epoxy acrylate, all at 75% in NVP. Shrinkage was determined from the density difference before and after UV cure. The density measurements were made in pycnometers at 25° C. 

If fhe dry volume V defermined using a pycnometer is measured, then the density of solids ps (i.e., grain density) is calculated directly MJV and the bulk density (p) is derived indirectly by adding the pore water mass (M ) and volume (V ) to the solid mass and volume. 

Mercury density via pycnometer, density gradient column Gravimetric measurement, vihrascope Optical microscopy... 

The specific gravity of milk can be used to determine the total solids (TS) content and is usually measured by either a standard hydrometer or with a pycnometer (density bottle) after gentle mixing. The effect of different temperatures can be corrected using a table. The TS of the milk can be calculated if the fat content is known by using Richmond s formula ... 

Figure 18.22. Gay-Lussac Type Pycnometer for Measuring True Density of liquids.

The mass density or simply density of the wood at a given moisture content, w (usually 12 wt.%), denoted by and expressed in kg.m corresponds to the mass of oven-dry wood and its contained water divided by its volume at the same moisture content. It is important to note that density measurements performed on the dry wood substance of several species with a hehum pycnometer gave an average density of 1460 kg.m Like specific gravity, two factors affect the density of wood ... 

A helium pycnometer is used to measure the true density of powder materials. The automated pycnometers run tests and report data from consecutive runs that are within a user-specified tolerance. This instrument can be used to perform particle density measurements on various composite and polymeric materials. 

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. 

The thermal diffusivity was measured by a laser flash method [[11]11]. Samples should be discshaped with equal dimension than the laser beam and having plane and parallel surfaces. Also, to suppose that heat transfer is unidirectional the sample thickness should be less than a tenth of the diameter [12]. Thermal conductivity (W.m K ) was calculated from thermal diffusivity a (m. s ), density p (kg.m ) and specific heat capacity Cp (J.kg K ) at each temperature using Eq 1. Specific heat capacities were measured with a differential scanning calorimeter. Density measurements were carried out with a pycnometer at room temperature (27°C) in methanol. 

When greater accuracy is required or when only small quantities are available, 1 iquid densities are best obtained from the mass required to fill a vessel of accurately defined volume, e.g., a specific gravity bottle (p.217) or a pycnometer. With careful technique, the densities measured with pycnometers are precise to five significant figures. 

Wort is the resnlt of enzymatic hydrolysis of the grist that results from the conversion of starch and proteins into solnble and simpler carbohydrates and peptides, respectively (Chapter 14). The most important wort properties are soluble solids or extract yield ( Plato), percent fermentable sngars, viscosity, pH, color, and alpha amino nitrogen (AAN), also known as free amino nitrogen (FAN). The most relevant determination is the wort density at the end of mashing because it allows processors to calculate the efficiency of solnbilizing the available extract. The most practical way is to determine the density as Plato using a pycnometer (ASBC Wort 3 method). The total extract is calculated by the volume of wort recovered x density x Plato. The volume and density measurements must be referenced to 20 C. Another useful assay... 

Method B of ASTM D 792 uses a gas pycnometer to measure the volume of a powder or a granulated or irregular solid. The displacement of gas, usually helium, from a vessel of known volume is measured by sensitive differential pressure indicators. Suitable laboratory equipment is manufactured by Quantochrome (UltraFoam Pycnometer), Micromeiitics (Accu Pyc 1330), and others. This is also a convenient route to foam density. In troubleshooting production problems, SpG should always be checked, because of its sensitivity to misformulation. 

The densities of most polymer dispersions are close to 1 g cm as the corresponding polymers (with the exception of polyvinyl chloride and poly(vinylidene chloride)) have densities in the range 1.0 to 1.2 g cm [2]. Since the densities of the polymer particles almost match the density of the aqueous phase, sedimentation is usually only a problem in emulsion polymers if they contain very coarse particles. Density measurements have been used in the past to follow the course of emulsion polymerization reactions, because the density of the monomer is usually lower than that of the polymer (densitometry [1]). Densities can, for instance, be determined quite simply with a pycnometer (see ISO 2811). Very high precision density measurements ( 5 X 10 g cm" ) are possible with a vibrating-tube densimeter [3]. In this method, the change in the resonant frequency of the tube, which depends on its total mass, is measured when the dispersion is placed in it. It is essential that the sample is wholly free of gas bubbles. 

The determination of oxygen isotopic content by density measurements has usually been restricted to the analysis of water (Kirshenbaum, 1951). Either pycnometers of floats may be used, but since this method needs meticulous purification (and normalization of the hydrogen isotope composition) of the water, as well as relatively large quantities for a single analysis, it is rarely used. A number of improvements in these methods have been recently reported by Lauder (1959) and by Kats and Lapteva (1959), but it is unlikely that it can be of any wide application in biochemical research. 

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