A pycnometer is usually made of glass , with a close-fitting ground glass stopper with a capillary tube through it, so that air bubbles may escape from the apparatus. This device enables a liquid's density to be measured accurately by reference to an appropriate working fluid, such as water or mercury , using an analytical balance. If the flask is weighed empty, full of water, and full of a liquid whose relative density is desired, the relative density of the liquid can easily be calculated.

The particle density of a powder, to which the usual method of weighing cannot be applied, can also be determined with a pycnometer. The powder is added to the pycnometer, which is then weighed, giving the weight of the powder sample.

Difference Between Density and Specific Gravity

The pycnometer is then filled with a liquid of known density, in which the powder is completely insoluble. The weight of the displaced liquid can then be determined, and hence the relative density of the powder.

A gas pycnometer , the gas-based manifestation of a pycnometer, compares the change in pressure caused by a measured change in a closed volume containing a reference usually a steel sphere of known volume with the change in pressure caused by the sample under the same conditions. The difference in change of pressure represents the volume of the sample as compared to the reference sphere, and is usually used for solid particulates that may dissolve in the liquid medium of the pycnometer design described above, or for porous materials into which the liquid would not fully penetrate.

When a pycnometer is filled to a specific, but not necessarily accurately known volume, V and is placed upon a balance, it will exert a force. The bottle is, of course, filled with air but as that air displaces an equal amount of air the weight of that air is canceled by the weight of the air displaced. Now we fill the bottle with the reference fluid e. The force exerted on the pan of the balance becomes:.

ASTM Test Methods - Pycnometry Instruments

If we subtract the force measured on the empty bottle from this or tare the balance before making the water measurement we obtain. The bottle is now emptied, thoroughly dried and refilled with the sample. The force, net of the empty bottle, is now:. The ratio of the sample and water forces is:. This is called the Apparent Relative Density, denoted by subscript A, because it is what we would obtain if we took the ratio of net weighings in air from an analytical balance or used a hydrometer the stem displaces air.

Note that the result does not depend on the calibration of the balance. The only requirement on it is that it read linearly with force. Nor does RD A depend on the actual volume of the pycnometer. In the usual case we will have measured weights and want the true relative density. This is found from. Since the density of dry air at Where the relative density of the sample is close to that of water for example dilute ethanol solutions the correction is even smaller. Hydrostatic Pressure-based Instruments : This technology relies upon Pascal's Principle which states that the pressure difference between two points within a vertical column of fluid is dependent upon the vertical distance between the two points, the density of the fluid and the gravitational force.

This technology is often used for tank gaging applications as a convenient means of liquid level and density measure.

Vibrating Element Transducers : This type of instrument requires a vibrating element to be placed in contact with the fluid of interest. The resonant frequency of the element is measured and is related to the density of the fluid by a characterization that is dependent upon the design of the element. In modern laboratories precise measurements of relative density are made using oscillating U-tube meters. These are capable of measurement to 5 to 6 places beyond the decimal point and are used in the brewing, distilling, pharmaceutical, petroleum and other industries.

The vibrating fork immersion probe is another good example of this technology. This technology also includes many coriolis-type mass flow meters which are widely used in chemical and petroleum industry for high accuracy mass flow measurement and can be configured to also output density information based on the resonant frequency of the vibrating flow tubes. Ultrasonic Transducer : Ultrasonic waves are passed from a source, through the fluid of interest, and into a detector which measures the acoustic spectroscopy of the waves. Fluid properties such as density and viscosity can be inferred from the spectrum.

Radiation-based Gauge : Radiation is passed from a source, through the fluid of interest, and into a scintillation detector, or counter. As the fluid density increases, the detected radiation "counts" will decrease. The source is typically the radioactive isotope cesium , with a half-life of about 30 years. A key advantage for this technology is that the instrument is not required to be in contact with the fluid—typically the source and detector are mounted on the outside of tanks or piping. Buoyant Force Transducer : the buoyancy force produced by a float in a homogeneous liquid is equal to the weight of the liquid that is displaced by the float.

Since buoyancy force is linear with respect to the density of the liquid within which the float is submerged, the measure of the buoyancy force yields a measure of the density of the liquid. The submersible probe head contains a mathematically characterized spring-float system. When the head is immersed vertically in the liquid, the float moves vertically and the position of the float controls the position of a permanent magnet whose displacement is sensed by a concentric array of Hall-effect linear displacement sensors.

The output signals of the sensors are mixed in a dedicated electronics module that provides a single output voltage whose magnitude is a direct linear measure of the quantity to be measured. Substances with a relative density of 1 are neutrally buoyant, those with RD greater than one are denser than water, and so ignoring surface tension effects will sink in it, and those with an RD of less than one are less dense than water, and so will float. From Wikipedia, the free encyclopedia. It has been suggested that Specific gravity be merged into this article. Discuss Proposed since August Main article: Hydrostatic weighing.

Main article: hydrometer. A text-book of mineralogy: with an extended treatise on crystallography Fuhs Fundamentals of fluid mechanics. Malting and Brewing Science, Vol. Managed Pressure Drilling. Retrieved July 10, — via sciencedirect. Retrieved on Laboratory equipment. Stands Clamps Holders. Dean—Stark Soxhlet extractor Kipp's. Boston round Pycnometer.

Cold finger Liebig. Evaporating Petri Syracuse Watch glass. Beaker Gas syringe Vial. Analytical chemistry. Personal protective equipment PPE. Lab coat Face shield Respirator Rubber apron Safety shower. Acid solvent cabinet Biosafety cabinet Fire blanket Fire extinguisher Fume hood. Figure 8: The basket used for underwater weighing. Figure 9: Weighing the sample underwater. Remove the aggregate from the water and dry it until it maintains a constant mass.

This indicates that all the water has left the sample. There are no minimum or maximum specific gravity or absorption values in Superpave mix design. Rather, specific gravity is an aggregate quality needed to make required volume calculations. Some state agencies specify minimum aggregate specific gravities or maximum percent water absorption to help control aggregate quality. Specific gravities can vary widely depending upon aggregate type.

Some lightweight shales not used in HMA production can have specific gravities near 1. Typically, aggregate used in HMA production will have a bulk specific gravity between about 2.

Difference Between Specific Gravity and Density

Bulk SSD specific gravities can be on the order of 0. For a particular aggregate type or source, fine aggregate specific gravities can be slightly higher than coarse aggregate specific gravities because as the aggregate particles get smaller, the fraction of pores exposed to the aggregate surface and thus excluded from the specific gravity calculation because they are water-permeable increases.

Aggregate absorption can also vary widely depending upon aggregate type. Some lightweight shales not used in HMA production can have absorptions approaching 30 percent, while other aggregate types can have near zero absorption. Typically, aggregate used in HMA production will have an absorption between just above zero and 5 percent. Absorptions above about 5 percent tend to make HMA mixtures uneconomical because extra asphalt binder is required to account for the high aggregate absorption. If absorption is incorrectly accounted for, the resulting HMA could be overly dry and have low durability absorption calculated lower than it actually is or over-asphalted and susceptible to distortion and rutting absorption calculated higher than it actually is.

Three different masses are recorded during the test. These masses are used to calculate the various specific gravities and absorption using the following equations:. In the apparent specific gravity calculation the mass of the SSD aggregate sample is replaced by the mass of the oven-dry aggregate sample A replaces B , which means that the water permeable voids within the aggregate are not included and A — C is the mass of water displaced by the oven-dry sample.

The ratios given in the equations are then simply the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water, which is specific gravity. A quick check of the results should show that bulk specific gravity is the lowest specific gravity, bulk SSD specific gravity is in the middle and apparent specific gravity is the highest. Overview The coarse aggregate specific gravity test Figure 1 is used to calculate the specific gravity of a coarse aggregate sample by determining the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water.

Apparent Specific Gravity, G sa.

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The volume measurement only includes the volume of the aggregate particle; it does not include the volume of any water permeable voids. The mass measurement only includes the aggregate particle. Apparent specific gravity is intended to only measure the specific gravity of the solid volume, therefore it will be the highest of the aggregate specific gravities.

specific gravity

It is formally defined as the ratio of the mass of a unit volume of the impermeable portion of aggregate does not include the permeable pores in aggregate to the mass of an equal volume of gas-free distilled water at the stated temperature. The volume measurement includes the overall volume of the aggregate particle as well as the volume of the water permeable voids.

Since it includes the water permeable void volume, bulk specific gravity will be less than apparent specific gravity.