Compressibility of mercury

Pressure m Megabars.1 Compressibility of Water. Compressibility of Mercury. 

Conversion factors for mercury manometer pressure units are calculated using die standard value for the acceleration of gravity and die density of mercury at die stated temperature. Additional digits are not justified because the definitions of the units do not take into account die compressibility of mercury or the change in density caused by the revised practical temperature scale, ITS-90. Similar comments also apply to water manometer pressure units. Conversion factors for conventional mercury and water manometer pressure units are based on ISO 31-3. 

Richards used the piezometer shown in Fig. 2.VIII D, which was contained in a steel cylinder containing mercury attached to a Cailletet pump. The mercury in the lower part of the bulb was electrically connected through a sealed-in platinum wire with that in the cylinder, and a platinum wire made contact with that in the capillary tube. The compressibility of mercury was first determined with the piezometer full of mercury, pressure being applied till the contact in the capillary was broken at about 100 atm., and then the pressure was slowly released till contact was again made. A further known amount of mercury was added and the process repeated at higher pressures. Part of the mercury in the piezometer was then replaced by a known volume of the liquid, and the amount of mercury adjusted so that contact was broken at the various pressures by adding small amounts of mercury before compression. These amounts differed from those added when the piezometer contained only mercury, and from the differences the compressibility of the liquid could be calculated, that of mercury being known. 

Mercury porosimetry was performed on monolithic samples outgassed down to 0.01 Pa for at least 2 h at room temperature. The samples were transferred to a Carlo Erba Pascal 140 porosimeter on which the mercury pressure was raised from ca 0.01 MPa to 0.1 MPa, and afterwards to a Carlo Erba Pascal 240 porosimeter on which the mercury pressure is further raised to 200 MPa. A blank curve was subtracted from the raw data to correct for the compressibility of mercury. 

The effect of compressibility of mercury, sample container, sample and residual air with increasing pressure. 

In order to calculate the true volume intrusion of mercury into the pores of a sample, a correction must be made to account for the compression of mercury, sample cell and sample [69]. The usual procedure is to carry out a blank experiment in the absence of a sample or with a non-porous sample [70]. During the course of calibration measurements on non-porous nylon it was found that a normal blank correction procedure led to erroneous mercury penetration volumes [71]. In particular it was found that the shape of the intrusion curve varied with the size of the sample. 

Fig. 4.9 Pressurizing curve for nylon. Ouncorrected curve, corrected by a blank run [Equation (4.6)], corrected for compressibility of mercury and glass [Equation (4.7)], corrected for compressibility of mercury, glass and sample [Equation (4.9)].

Additionally, a blank correction must be included to compensate for the compressibility of mercury and the deformation of the dilatometer. The blank is specific to each dilatometer and must be carried out after each... 

The incorporation of the new material without any increase in the overall length of the book has been achieved in part by extensive re-writing, with the compression of earlier material, and in part by restricting the scope to the physical adsorption of gases (apart from a section on mercury porosimetry). The topics of chemisorption and adsorption from solution, both of which were dealt with in some detail in the first edition, have been omitted chemisorption processes are obviously dependent on the chemical nature of the surface and therefore cannot be relied upon for the determination of the total surface area and methods based on adsorption from solution have not been developed, as was once hoped, into routine procedures for surface area determination. Likewise omitted, on grounds of... 

A further rising of the reservoir causes a compression of the gas in the capillary C (closed). Capillary D is open and connected to the vacuum system. The difference Ah between the two mercury heights corresponds to a pressure difference Ap = pg-Ah (Ah in mm gives numerically Ap in torr) p is the density of mercury. If the compression of the gas in B and C is isothermal, we can write ... 

Measurements of particle porosity are a valuable supplement to studies of specific surface area, and such data are particularly useful in the evaluation of materials used in direct compression processes. For example, both micromeritic properties were measured for several different types of cellulosic-type excipients [53]. Surface areas by the B.E.T. method were used to evaluate all types of pore structures, while the method of mercury intrusion porosimetry used could not detect pores smaller than 10 nm. The data permitted a ready differentiation between the intraparticle pore structure of microcrystalline and agglomerated cellulose powders. 

The compressibility of solutions are determined by measuring the volume change of Hg in the capillary when various pressures are applied to the system. The change in height of the meniscus (Ah) and the pressure change (AP) are dependent upon the volume of mercury (VHg), the volume of the solution (Vg0 n), and the inside volume of the glass container to a reference mark (Ah). 

The effects of mercury compression and the compressive heating of the hydraulic oil are thermodynamically compensated. Therefore, the need to make blank runs is unnecessary for all but the most exacting analysis. Blank runs made on cells filled with mercury show less than 1 % of full-scale signal over the entire operating range from 0 to 60000psi. 

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