Bulk density

Bulk density, also called apparent density or volumetric density, is a property of powders, granules, and other "divided" solids, especially used in reference to mineral components (soil, gravel), chemical substances, (pharmaceutical) ingredients, foodstuff, or any other masses of corpuscular or particulate matter. It is defined as the mass of many particles of the material divided by the total volume they occupy. The total volume includes particle volume, inter-particle void volume, and internal pore volume.[1]

Bulk density is not an intrinsic property of a material; it can change depending on how the material is handled. For example, a powder poured into a cylinder will have a particular bulk density; if the cylinder is disturbed, the powder particles will move and usually settle closer together, resulting in a higher bulk density. For this reason, the bulk density of powders is usually reported both as "freely settled" (or "poured" density) and "tapped" density (where the tapped density refers to the bulk density of the powder after a specified compaction process, usually involving vibration of the container.[2])


The bulk density of soil depends greatly on the mineral make up of soil and the degree of compaction. The density of quartz is around 2.65 g/cm³ but the (dry) bulk density of a mineral soil is normally about half that density, between 1.0 and 1.6 g/cm³. Soils high in organics and some friable clay may have a bulk density well below 1 g/cm³. The reason why soils rich in soil organic carbon do have lower bulk density is due to the low density of organic materials. For instance peat soils have bulk densities from 0.02 g/cm³ to 0.98  g/cm³.[3]

Bulk density of soil is usually determined from a core sample which is taken by driving a metal corer into the soil at the desired depth and horizon.[4] This gives a soil sample of known total volume, . From this sample the wet bulk density and the dry bulk density can be determined.[5]

For the wet bulk density (total bulk density) this sample is weighed, giving the mass . For the dry bulk density, the sample is oven dried and weighed, giving the mass of soil solids, . The relationship between these two masses is , where is the mass of substances lost on oven drying (often, mostly water). The dry and wet bulk densities are calculated as

Dry bulk density = mass of soil/ volume as a whole

Wet bulk density = mass of soil plus liquids/ volume as a whole

The dry bulk density of a soil is inversely related to the porosity of the same soil: the more pore space in a soil the lower the value for bulk density. Bulk density of a region in the interior of the earth is also related to the seismic velocity of waves travelling through it: for P-waves, this has been quantified with Gardner's relation. The higher the density, the faster the velocity.

See also


  1. ^ Page 50 in Buckman, Harry O.; Brady, Nyle C. (1960), The Nature and Property of Soils - A College Text of Edaphology (6th ed.), New York: Macmillan Publishers, New York, NY
  2. ^ "Powder Bulk Density - Bulk Solids density - Bulk Powder Properties - Powder Loose Density - Powder tapped density - PowderProcess.net". www.powderprocess.net. Retrieved 2018-02-22.
  3. ^ Soane, B.D. (1990). "The role of organic matter in soil compactibility: A review of some practical aspects". Soil and Tillage Research. 16 (1–2): 179–201. doi:10.1016/0167-1987(90)90029-D.
  4. ^ USDA Natural Resources Conservation Service "Soil quality indicators -- Bulk density" retrieved December 5, 2013
  5. ^ Argonne National Lab "RESRAD Data collection handbook, chapter 2 -- Soil density" retrieved May 26, 2012

External links

6 Hebe

Hebe ( HEE-bee; minor planet designation: 6 Hebe) is a large main-belt asteroid, containing around half a percent of the mass of the belt. However, due to its apparently high bulk density (greater than that of the Moon or even Mars), Hebe does not rank among the top twenty asteroids by volume. This high bulk density suggests an extremely solid body that has not been impacted by collisions, which is not typical of asteroids of its size – they tend to be loosely-bound rubble piles.

In brightness, Hebe is the fifth-brightest object in the asteroid belt after Vesta, Ceres, Iris, and Pallas. It has a mean opposition magnitude of +8.3, about equal to the mean brightness of Titan, and can reach +7.5 at an opposition near perihelion.

Hebe is probably the parent body of the H chondrite meteorites, which account for about 40% of all meteorites striking Earth.

Alberger process

The Alberger process is a method of producing salt.

Bituminous coal

Bituminous coal or black coal is a relatively soft coal containing a tarlike substance called bitumen or asphalt. It is of higher quality than lignite coal but of poorer quality than anthracite. Formation is usually the result of high pressure being exerted on lignite. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the seams. These distinctive sequences, which are classified according to either "dull, bright-banded" or "bright, dull-banded", is how bituminous coals are stratigraphically identified.

Bituminous coal is an organic sedimentary rock formed by diagenetic and sub metamorphic compression of peat bog material. Its primary constituents are macerals: vitrinite, and liptinite. The carbon content of bituminous coal is around 60–80%; the rest is composed of water, air, hydrogen, and sulfur, which have not been driven off from the macerals. Bank density is approximately 1346 kg/m³ (84 lb/ft³). Bulk density typically runs to 833 kg/m³ (52 lb/ft³).

The heat content of bituminous coal ranges from 24 to 35 MJ/kg (21 million to 30 million BTU per short ton) on a moist, mineral-matter-free basis.

Within the coal mining industry, this type of coal is known for releasing the largest amounts of firedamp, a dangerous mixture of gases that can cause underground explosions. Extraction of bituminous coal demands the highest safety procedures involving attentive gas monitoring, good ventilation and vigilant site management.

Carr index

The Carr index (also: Carr's index or Carr's Compressibility Index) is an indication of the compressibility of a powder. It is named after the scientist Ralph J. Carr, Jr.

The Carr index is calculated by the formula , where is the freely settled bulk density of the powder, and is the tapped bulk density of the powder after "tapping down". It can also be expressed as .

The Carr index is frequently used in pharmaceutics as an indication of the flowability of a powder. In a free-flowing powder, the bulk density and tapped density would be close in value, therefore, the Carr index would be small. On the other hand, in a poor-flowing powder where there are greater interparticle interactions, the difference between the bulk and tapped density observed would be greater, therefore, the Carr index would be larger. A Carr index greater than 25 is considered to be an indication of poor flowability, and below 15, of good flowability.

Another way to measure the flow of a powder is the Hausner ratio, which can be expressed as .

Both the Hausner ratio and the Carr index are sometimes criticized, despite their relationships to flowability being established empirically, as not having a strong theoretical basis. Use of these measures persists, however, because the equipment required to perform the analysis is relatively cheap and the technique is easy to learn.

Density logging

Density logging is a well logging tool that can provide a continuous record of a formation's bulk density along the length of a borehole. In geology, bulk density is a function of the density of the minerals forming a rock (i.e. matrix) and the fluid enclosed in the pore spaces. This is one of three well logging tools that are commonly used to calculate porosity, the other two being sonic logging and neutron porosity logging

Dry quicksand

Dry quicksand is loose sand whose bulk density is reduced by blowing air through it and which yields easily to weight or pressure. It acts similarly to normal quicksand, but it does not contain any water and does not operate on the same principle. Dry quicksand is an example of a granular material.

Historically, the existence of dry quicksand was doubted, and the reports of humans and complete caravans being lost in dry quicksand were considered to be folklore. In 2004, it was created in the laboratory, but it is still not clear what its actual prevalence in nature is.

Fumed silica

Fumed silica (CAS number 112945-52-5), also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density and high surface area. Its three-dimensional structure results in viscosity-increasing, thixotropic behavior when used as a thickener or reinforcing filler.

Gardner's relation

Gardner's relation, or Gardner's equation, named after G. H. F. Gardner and L. W. Gardner, is an empirically derived equation that relates seismic P-wave velocity to the bulk density of the lithology in which the wave travels. The equation reads:

where is bulk density given in g/cm3, is P-wave velocity given in ft/s, and and are empirically derived constants that depend on the geology. Gardner et al. proposed that one can obtain a good fit by taking and . Assuming this, the equation is reduced to:

where the unit of is feet/s.

If is measured in m/s, and the equation is:

This equation is very popular in petroleum exploration because it can provide information about the lithology from interval velocities obtained from seismic data. The constants and are usually calibrated from sonic and density well log information but in the absence of these, Gardner's constants are a good approximation.

HD 3167

HD 3167 is a single, orange-hued star in the zodiac constellation of Pisces that hosts a system with three exoplanets. The star is too faint to be seen with the naked eye, having an apparent visual magnitude of 8.97. The distance to HD 3167 can be determined from its annual parallax shift of 21.12 mas as measured by the Gaia space observatory, yielding a range of 154 light years. It has a relatively high proper motion, traversing the celestial sphere at the rate of 0.204″ per year. Since it was first photographed during the Palomar observatory sky survey in 1953, it had moved over 12.5″ by 2017. The star is moving away from the Earth with an average heliocentric radial velocity of +19.5 km/s.This is an ordinary K-type main-sequence star with a stellar classification of K0 V and no significant variability. The star has 86% of the mass of the Sun and 86% of the Sun's radius. This gives it a bulk density of 5.60+2.15−1.43 g/cm3. It is a chromospherically inactive star and is radiating 56% of the Sun's luminosity from its photosphere at an effective temperature of 5,261 K. The spin of the star displays a relatively low projected rotational velocity of around 1.7 km/s. It has a near solar metallicity – a term astronomers use for the proportion of elements other than hydrogen and helium in a stellar atmosphere.

Hausner ratio

The Hausner ratio is a number that is correlated to the flowability of a powder or granular material. It is named after the engineer Henry H. Hausner (1900–1995).

The Hausner ratio is calculated by the formula

where is the freely settled bulk density of the powder, and is the tapped bulk density of the powder. The Hausner ratio is not an absolute property of a material; its value can vary depending on the methodology used to determine it.

The Hausner ratio is used in a wide variety of industries as an indication of the flowability of a powder. A Hausner ratio greater than 1.25 is considered to be an indication of poor flowability. The Hausner ratio (H) is related to the Carr index (C), another indication of flowability, by the formula . Both the Hausner ratio and the Carr index are sometimes criticized, despite their relationships to flowability being established empirically, as not having a strong theoretical basis. Use of these measures persists, however, because the equipment required to perform the analysis is relatively cheap and the technique is easy to learn.


In both the World Reference Base for Soil Resources (WRB) and the USDA soil taxonomy, a Histosol is a soil consisting primarily of organic materials. They are defined as having 40 centimetres (16 in) or more of organic soil material in the upper 80 centimetres (31 in). Organic soil material has an organic carbon content (by weight) of 12 to 18 percent, or more, depending on the clay content of the soil. These materials include muck (sapric soil material), mucky peat (hemic soil material), or peat (fibric soil material). Aquic conditions or artificial drainage are required. Typically, Histosols have very low bulk density and are poorly drained because the organic matter holds water very well. Most are acidic and many are very deficient in major plant nutrients which are washed away in the consistently moist soil.

Histosols are known by various other names in other countries, such as peat or muck. In the Australian Soil Classification, Histosols are called Organosols.Histosols form whenever organic matter forms at a more rapid rate than it is destroyed. This occurs because of restricted drainage precluding aerobic decomposition, and the remains of plants and animals remain within the soil. Thus, Histosols are very important ecologically because they, and Gelisols, store large quantities of organic carbon. If accumulation continues for a long enough period, coal forms.

Most Histosols occur in Canada, Scandinavia, the West Siberian Plain, Sumatra, Borneo and New Guinea. Smaller areas are found in other parts of Europe, the Russian Far East (chiefly in Khabarovsk Krai and Amur Oblast), Florida and other areas of permanent swampland. Fossil Histosols are known from the earliest extensive land vegetation in the Devonian.

Histosols are generally very difficult to cultivate because of the poor drainage and often low chemical fertility. However, Histosols formed on very recent glacial lands can often be very productive when drained and produce high-grade pasture for dairying or beef cattle. They can sometimes be used for fruit if carefully managed, but there is a great risk of the organic matter becoming dry powder and eroding under the influence of drying winds. A tendency towards shrinkage and compaction is also evident with crops.

Like Gelisols, Histosols have greatly restricted use for civil engineering purposes because heavy structures tend to subside in the wet soil.

In USDA soil taxonomy, Histosols are subdivided into:

Folists – Histosols that are not saturated with water for long periods of time during the year.

Fibrists – Histosols that are primarily made up of only slightly decomposed organic materials, often called peat.

Hemists – Histosols that are primarily made up of moderately decomposed organic materials.

Saprists – Histosols that are primarily made up of highly decomposed organic materials, often called muck.

Particle density (packed density)

The particle density or true density of a particulate solid or powder, is the density of the particles that make up the powder, in contrast to the bulk density, which measures the average density of a large volume of the powder in a specific medium (usually air).

The particle density is a relatively well-defined quantity, as it is not dependent on the degree of compaction of the solid, whereas the bulk density has different values depending on whether it is measured in the freely settled or compacted state (tap density). However, a variety of definitions of particle density are available, which differ in terms of whether pores are included in the particle volume, and whether voids are included.

Pore space in soil

The pore space of soil contains the liquid and gas phases of soil, i.e., everything but the solid phase that contains mainly minerals of varying sizes as well as organic compounds.

In order to understand porosity better a series of equations have been used to express the quantitative interactions between the three phases of soil.

Macropores or fractures play a major role in infiltration rates in many soils as well as preferential flow patterns, hydraulic conductivity and evapotranspiration. Cracks are also very influential in gas exchange, influencing respiration within soils. Modeling cracks therefore helps understand how these processes work and what the effects of changes in soil cracking such as compaction, can have on these processes.


Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the "accessible void", the total amount of void space accessible from the surface (cf. closed-cell foam). There are many ways to test porosity in a substance or part, such as industrial CT scanning. The term porosity is used in multiple fields including pharmaceutics, ceramics, metallurgy, materials, manufacturing, hydrology, earth sciences, soil mechanics and engineering.


A reclaimer is a large machine used in bulk material handling applications. A reclaimer's function is to recover bulk material such as ores and cereals from a stockpile. A stacker is used to stack the material.

Reclaimers are volumetric machines and are rated in m3/h (cubic meters per hour) for capacity, which is often converted to t/h (tonnes per hour) based on the average bulk density of the material being reclaimed. Reclaimers normally travel on a rail between stockpiles in the stockyard. A bucket wheel reclaimer can typically move in three directions: horizontally along the rail; vertically by "luffing" its boom and rotationally by slewing its boom. Reclaimers are generally electrically powered by means of a trailing cable.

Rubble pile

In astronomy, a rubble pile is a celestial body that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between the various chunks that make them up.

Asteroids Bennu and Ryugu have a measured bulk density which suggests a rubble pile internal structure. Many comets and most smaller minor planets are thought to be composed of coalesced rubble.

Secondary succession

Secondary succession is one of the two types ecological succession of a plants life. As opposed to the first, primary succession, secondary succession is a process started by an event (e.g. forest fire, harvesting, hurricane, etc.) that reduces an already established ecosystem (e.g. a forest or a wheat field) to a smaller population of species, and as such secondary succession occurs on preexisting soil whereas primary succession usually occurs in a place lacking soil. Many factors can affect secondary succession, such as trophic interaction, initial composition, and competition-colonization trade-offs. The factors that control the increase in abundance of a species during succession may be determined mainly by seed production and dispersal, micro climate; landscape structure (habitat patch size and distance to outside seed sources); bulk density, pH, and soil texture (sand and clay).Simply put, secondary succession is the ecological succession that occurs after the initial succession has been disrupted and some plants and animals still exist. It is usually faster than primary succession

Soil is already present

Seeds, roots and underground vegetative organs of plants may still survive in the soil.

Tropical peat

Tropical peat is a type of histosol that found in tropical latitude, including South East Asia, Africa, and Central and South America. Tropical peat mostly consists of dead organic matter from trees instead of spaghnum which are commonly found in temperate peat. This soil usually contain high organic matter content, exceeding 75% with dry low bulk density around 0.2 mg/m3 (0.0 gr/cu ft).Areas of tropical peat are found mostly in South East Asia (about 70% by area) although are also found in Africa, Central and South America and elsewhere around the Pacific Ocean. Tropical peatlands are significant carbon sinks and store large amounts of carbon and their destruction can significantly impact on the amount of atmospheric carbon dioxide. Tropical peatlands are vulnerable to destabilisation through human and climate induced changes. Estimates of the area (and hence volume) of tropical peatland vary but a reasonable estimate is in the region of 380,000 square kilometres (150,000 sq mi).

Although tropical peatlands only cover about 0.25% of the Earth's land surface they contain 50,000-70,000 million tonnes of carbon (about 3% global soil carbon). In addition, tropical peatlands support diverse ecosystems and are home to a number of endangered species including the Orangutan.

The native peat swamp forests contain a number of valuable timber-producing trees plus a range of other products of value to local communities, such as bark, resins and latex. Land-use changes and fire, mainly associated with plantation development and logging (deforestation and drainage), are reducing this carbon store and contributing to greenhouse gas (GHG) emissions.

The problems that result from development of tropical peatland stem mainly from a lack of understanding of the complexities of this ecosystem and the fragility of the relationship between peat and forest. Once the forest is removed and the peat is drained, the surface peat oxidises and loses stored carbon rapidly to the atmosphere (as carbon dioxide). This results in progressive loss of the peat surface, leading to local flooding and, due to the large areas involved, global climate change. Failure to account for such emissions results in underestimates of the rate of increase in atmospheric GHGs and the extent of human induced climate change.

Uranium tetrafluoride

Uranium tetrafluoride (UF4) is a green crystalline solid compound of uranium with an insignificant vapor pressure and very slight solubility in water. Uranium in its tetravalent (uranous) state is very important in different technological processes. In the uranium refining industry it is known as green salt.

UF4 is generally an intermediate in the conversion of uranium hexafluoride (UF6) to either uranium oxides (U3O8 or UO2) or uranium metal. It is formed by the reaction of UF6 with hydrogen gas in a vertical tube-type reactor or by the action of hydrogen fluoride (HF) on uranium dioxide. UF4 is less stable than the uranium oxides and reacts slowly with moisture at ambient temperature, forming UO2 and HF, the latter of which is very corrosive; it is thus a less favorable form for long-term disposal. The bulk density of UF4 varies from about 2.0 g/cm3 to about 4.5 g/cm3 depending on the production process and the properties of the starting uranium compounds.

A molten salt reactor design, a type of nuclear reactor where the working fluid is a molten salt, would use UF4 as the core material. UF4 is generally chosen over other salts because of the usefulness of the elements without isotope separation, better neutron economy and moderating efficiency, lower vapor pressure and better chemical stability.

Like all uranium salts, UF4 is toxic and thus harmful by inhalation, ingestion, and through skin contact.


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