Density measurement liquids

Density Measurement, Liquid density can be obtained by measuring the differential pressure that exists in the liquid phase over a known height. An accuracy of i 1/2 per cent was obtained using a strain gage differential pressure cell with our scale set-up. We believe i 1/4 per cent can be realized on larger systems with the same or similar instrumentation. 

Mathews and Rawlings (1998) successfully applied model-based control using solids hold-up and liquid density measurements to control the filtrability of a photochemical product. Togkalidou etal. (2001) report results of a factorial design approach to investigate relative effects of operating conditions on the filtration resistance of slurry produced in a semi-continuous batch crystallizer using various empirical chemometric methods. This method is proposed as an alternative approach to the development of first principle mathematical models of crystallization for application to non-ideal crystals shapes such as needles found in many pharmaceutical crystals. 

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). 

Torklep and 0ye measured the viscosity of NaCl by this method, which has been adopted as the standard (see Section 1.2). The accuracy of the working equation is better than 0.1% for the cylinder geometry, hquid densities, and liquid viscosities used by these authors. They claim that the remarkable theoretical analysis of oscillating-body viscometers given by Kestin and Newell supersedes all former, less accurate theories. All the results were once suspect owing to possible solid impurities in the liquid. 

The density of a material is a function of temperature and pressure but its value at some standard condition (for example, 293.15 K or 298.15 K at either atmospheric pressure or at the vapor pressure of the compound) often is used to characterize a compound and to ascertain its purity. Accurate density measurements as a function of temperature are important for custody transfer of materials when the volume of the material transferred at a specific temperature is known but contracts specify the mass of material transferred. Engineering applications utilize the density of a substance widely, frequently for the efficient design and safe operation of chemical plants and equipment. The density and the vapor pressure are the most often-quoted properties of a substance, and the properties most often required for prediction of other properties of the substance. In this volume, we do not report the density of gases, but rather the densities of solids as a function of temperature at atmospheric pressure and the densities of liquids either at atmospheric pressure or along the saturation line up to the critical temperature. 

The purpose of this compilation is to tabulate the densities of compounds, hence only minimal description of experimental methods used to measure the density of liquids or solids appears. Detailed descriptions of methods for density determination of solids, liquids and gases, along with appropriate density reference standards, appear in a chapter by Davis and Koch in Physical Methods of Chemistry, Volume VI, Determination of Thermodynamic Properties [86-ros/bae],... 

The principal experimental method used to measure the density of a solid is determination of the mass of liquid displaced by a known mass of solid. It is essential that the solid have no appreciable solubility in the liquid, that all occluded air be removed from the solid and that the density of the displacement fluid be less than that of the solid lest the solid float. Densities of crystalline solids also can be determined from the dimensions of the unit cell. Davis and Koch discuss other methods for measuring the density of liquids and solids such as hydrostatic weighing of a buoy and flotation methods. 

Most measurements of densities of liquids below their normal boiling points are made in the presence of air. Densities reported here refer to liquids in equilibrium with a gas phase consisting of a mixture or air and vapor at a total pressure of one atmosphere below the normal boiling point and of vapor at the equilibrium vapor pressure above the boiling point. Thus air is not regarded as an impurity. 

The three most common ways of obtaining true density measurements are gas pycnometry (gas displacement), liquid displacement, and flotation in a liquid. These three techniques have been compared based on accuracy, ease of use, and instrumentation [63], and the results are summarized in Table 4. Gas pycnometry will be discussed in this section because of its wide use and ease of operation. 

Porosity calculations from density measurements have also been applied to granulations prepared using different processes. The method of granulation, such as the type of adjuvant used [64] or the amount of granulation liquid [74], was found to change the bulk density and porosity of the material. Consequently, the compression and flow properties of the materials were also different. 

Vibrating Flow Densimeter. One of the major advances made in making density measurements of solutions was the system developed by Kratky et al. (21) which measures the natural vibration frequency of a tube containing a liquid. The oscillating frequency (f) of the tube is related to its mass (m) by... 

Surface tension and density of liquid alloys have been studied by Moser et al. (2006). Measurements by maximum bubble pressure and dilatometric techniques were carried out in an extensive range of temperatures on liquid alloys close to the ternary eutectic Sn3 3Ag0 76Cu with different Sb additions, which decrease surface tension and density. The experimental data were discussed in comparison also with values calculated on the basis of different models. 

With these factors in mind, a new method to evaluate the conformation of an amphiphilic molecule at the site of interest was Introduced. The method is built on the fact that the determination of Interlayer spacings of a lamellar liquid crystal using low angle X-ray diffraction methods in combination with density measurements will provide sufficient information to calculate the cross-sectional areas occupied by each amphiphlle (19). 

Vapor density measurements (37, 226) and mass spectroscopy (226, 300) were used to show that ClFgO is monomeric in the gas phase. The relatively high boiling point and Trouton constant of ClFgO imply its association in the liquid phase. More specific evidence about the nature of this association was obtained from the vibrational spectra... 

When the specific rotation ([a]) of a pure liquid is reported (indicated by the term neat) its density dmust be referred to. An error is introduced into the specific rotation when the density measurement is inaccurate. Therefore, the rotation of a pure, undiluted sample can be quoted in an alternative way by the observed optical rotation a and the cell path length l (in decimeters). A typical standard form for correctly reporting the specific rotation of a pure liquid is as follows for trans- —)-(2S. 3S)-2.3-dimethyloxirane34 (ee >99%) ... 

Values of molar volumes can be calculated from densities measured for the liquid salt, or can be calculated as for hypothetical subcooled liquid at 298.15 K using the group contribution method [47]. As expected, the molar volumes of 1,3-dialkylimidazolium salts and quaternary ammonium salts increase progressively as the length of alkyl chain of the substituent increases. Some molar volumes values at 298.15 K are listed in Table 1.3. 

Specific gravity (sp gr) is a measure of the relative weight of one liquid compared to a universally familiar liquid, generally water. More specifically, sp gr is a ratio of the density of a liquid divided by the density of liquid water at 16°C (60°F). Specific gravities of selected liquids are shown in Table 1. 

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. 

Care must be taken to exclude air bubbles when weighing in water, and this is helped if a trace of detergent is added and/or the test piece quickly dipped in ethanol before weighing. If the rubber is less dense than water, then a sinker must be used in the same manner as for density measurements (see Chapter 7). The test piece is then immersed in the test liquid for the chosen time at the chosen temperature. At least 15 times the test piece volume of liquid should be used and care must be taken to ensure that the rubber is exposed on all sides to the liquid. This can be done by suspending the test pieces on wires or it is satisfactory to rest them on glass marbles. 

---