Vertebrates comprise all species of animals within the subphylum Vertebrata. Vertebrates represent the overwhelming majority of the phylum Chordata, with about 69,276 species described. Vertebrates include the jawless fishes and jawed vertebrates, which include the cartilaginous fishes and the bony fishes; the bony fishes in turn, cladistically speaking include the tetrapods, which include amphibians, reptiles and mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, at up to 33 m. Vertebrates make up less than five percent of all described animal species; the vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, the lampreys, do. Hagfish do, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as "Craniata" when discussing morphology. Molecular analysis since 1992 has suggested that hagfish are most related to lampreys, so are vertebrates in a monophyletic sense.
Others consider them a sister group of vertebrates in the common taxon of craniata. The word vertebrate derives from the Latin word vertebratus. Vertebrate is derived from the word vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic chordate body plan: a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it and the gastrointestinal tract below. In all vertebrates, the mouth is found at, or right below, the anterior end of the animal, while the anus opens to the exterior before the end of the body; the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. The defining characteristic of a vertebrate is the vertebral column, in which the notochord found in all chordates has been replaced by a segmented series of stiffer elements separated by mobile joints. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon and coelacanth.
Jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills; the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch; the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their chordate relatives have more than 50 pairs of gills. In amphibians and some primitive bony fishes, the larvae bear external gills, branching off from the gill arches; these are reduced in adulthood, their function taken over by the gills proper in fishes and by lungs in most amphibians. Some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish being irrevocably lost early in the evolution of tetrapods.
While the more derived vertebrates lack gills, the gill arches form during fetal development, form the basis of essential structures such as jaws, the thyroid gland, the larynx, the columella and, in mammals, the malleus and incus. The central nervous system of vertebrates is based on a hollow nerve cord running along the length of the animal. Of particular importance and unique to vertebrates is the presence of neural crest cells; these are progenitors of stem cells, critical to coordinating the functions of cellular components. Neural crest cells migrate through the body from the nerve cord during development, initiate the formation of neural ganglia and structures such as the jaws and skull; the vertebrates are the only chordate group to exhibit cephalisation, the concentration of brain functions in the head. A slight swelling of the anterior end of the nerve cord is found in the lancelet, a chordate, though it lacks the eyes and other complex sense organs comparable to those of vertebrates.
Other chordates do not show any trends towards cephalisation. A peripheral nervous system branches out from the nerve cord to innervate the various systems; the front end of the nerve tube is expanded by a thickening of the walls and expansion of the central canal of spinal cord into three primary brain vesicles: The prosencephalon and rhombencephalon, further differentiated in the various vertebrate groups. Two laterally placed eyes form around outgrowths from the midbrain, except in hagfish, though this may be a secondary loss; the forebrain is well developed and subdivided in most tetrapods, while the midbrain dominates in many fish and some salamanders. Vesicles of the forebrain are paired, giving rise to hemispheres like the cerebral hemispheres in mammals; the resulting anatomy of the central nervous system, with a single hollow nerve cord topped by a series of vesicles, is unique to vertebrates. All invertebrates with well-developed brains, such as insects and squids, have a ventral rather than dorsal system of ganglions, with a split brain stem running on each side of the mouth or gut.
Vertebrates originated about 525 million years ago during the Cambrian explosion, which saw
The Kola Peninsula is a peninsula in the far northwest of Russia. Constituting the bulk of the territory of Murmansk Oblast, it lies completely inside the Arctic Circle and is bordered by the Barents Sea in the north and the White Sea in the east and southeast; the city of Murmansk is the most populous human settlement on the peninsula, with a population of over 300,000 as of the 2010 Census. While the north of the peninsula was settled in the 7th–5th millennium BCE, the rest of its territory remained uninhabited until the 3rd millennium BCE, when various peoples started to arrive from the south. However, by the 1st millennium CE only the Sami people remained; this changed in the 12th century, when Russian Pomors discovered the peninsula's game and fish riches. Soon after, the Pomors were followed by the tribute collectors from the Novgorod Republic, the peninsula became a part of the Novgorodian lands. No permanent settlements, were established by the Novgorodians until the 15th century; the Novgorod Republic lost control of the peninsula to the Grand Duchy of Moscow in 1471, but the Russian migration did not stop.
Several new settlements were established during the 16th century, the Sami and Pomor people were forced into serfdom. In the second half of the 16th century, the peninsula became a subject of dispute between the Tsardom of Russia and the Kingdom of Denmark–Norway, which resulted in the strengthening of the Russian position. By the end of the 19th century, the indigenous Sami population had been forced north by the Russians as well as by newly arriving Izhma Komi and Kominized Nenets, who migrated here to escape a reindeer disease epidemic in their home lands in the southeast of the White Sea; the original administrative and economic center of the area was Kola, situated at the estuary of the Kola River into the Kola Bay. However, in 1916, Romanov-na-Murmane was founded and became the largest city and port on the peninsula; the Soviet period saw a rapid increase of the population, although most of it remained confined to urbanized territories along the sea coast and the railroads. The Sami people were subject to forced collectivization, including forced relocation to Lovozero and other centralized settlements, overall the peninsula was industrialized and militarized due to its strategic position and the discovery of the vast apatite deposits in the 1920s.
As a result, the ecology of the peninsula suffered major ecological damage, including contamination by military nuclear waste and nickel smelting. After the dissolution of the Soviet Union, the economy went into decline and the population started to decrease. Between 1989 and 2002, Murmansk Oblast lost a quarter of its population; the economy rebounded somewhat in the first decade of the 2000s and the peninsula remains the most industrially developed and urbanized region in northern Russia. Despite the peninsula's northerly location, its proximity to the Gulf Stream leads to unusually high temperatures in winter, but results in high winds due to the temperature variations between land and the Barents Sea. Summers are rather chilly, with the average July temperature of only 11 °C; the peninsula is covered by taiga in the south and tundra in the north, where permafrost limits the growth of the trees resulting in landscape dominated by shrubs and grasses. The peninsula supports a small variety of mammals, its rivers are an important habitat for the Atlantic salmon.
The Kandalaksha Nature Reserve, established to protect the population of common eider, is located in the Kandalaksha Gulf. The peninsula is located in the far northwest of Russia completely inside the Arctic Circle and is washed by the Barents Sea in the north and the White Sea in the east and southeast. Geologically, the peninsula occupies the northeastern edge of the Baltic Shield; the western border of the peninsula stretches along the meridian from the Kola Bay through the valley of the Kola River, Lake Imandra, the Niva River to the Kandalaksha Gulf, although some sources push it all the way west to Russia's border with Finland. Under a more restrictive definition, the peninsula covers an area of about 100,000 square kilometers; the northern coast is high, while the southern coast is flat. The western part of the peninsula is covered by two mountain ranges: the Khibiny Mountains and the Lovozero Massif; the Keyvy drainage divide lies in the central part. The mountainous reliefs of the Murman and Kandalaksha Coasts stretch from southeast to northwest, mirroring the peninsula's main orographic features.
Administratively, the territory of the peninsula consists of Lovozersky and Tersky Districts, parts of Kandalakshsky and Kolsky Districts, as well as the territories subordinated to the cities and towns of Murmansk, Severomorsk and parts of the territories subordinated to Apatity and Polyarnye Zori. Because the last ice age removed the top sediment layer of the soil, the Kola Peninsula is on the surface rich in various ores and minerals, including apatites and nephelines. Deposits of construction materials such as granite and limestone are abundant. Diatomaceous earth deposits are used to produce insulation. Proximity of
Milk is a nutrient-rich, white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for infant mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to its young and can reduce the risk of many diseases, it contains many other nutrients including lactose. Interspecies consumption of milk is not uncommon among humans, many of whom consume the milk of other mammals; as an agricultural product, milk called dairy milk, is extracted from farm animals during or soon after pregnancy. Dairy farms produced about 730 million tonnes of milk from 260 million dairy cows. India is the world's largest producer of milk, is the leading exporter of skimmed milk powder, yet it exports few other milk products; the increasing rise in domestic demand for dairy products and a large demand-supply gap could lead to India being a net importer of dairy products in the future. The United States, India and Brazil are the world's largest exporters of milk and milk products.
China and Russia were the world's largest importers of milk and milk products until 2016 when both countries became self-sufficient, contributing to a worldwide glut of milk. Throughout the world, more than six billion people consume milk products. Over 750 million people live in dairy farming households; the term "milk" comes from "Old English meoluc, from Proto-Germanic *meluks "milk"". Milk consumption occurs in two distinct overall types: a natural source of nutrition for all infant mammals and a food product obtained from other mammals for consumption by humans of all ages. In all mammals, milk is fed to infants through breastfeeding, either directly or by expressing the milk to be stored and consumed later; the early milk from mammals is called colostrum. Colostrum contains antibodies that provide protection to the newborn baby as well as nutrients and growth factors; the makeup of the colostrum and the period of secretion varies from species to species. For humans, the World Health Organization recommends exclusive breastfeeding for six months and breastfeeding in addition to other food for up to two years of age or more.
In some cultures it is common to breastfeed children for three to five years, the period may be longer. Fresh goats' milk is sometimes substituted for breast milk, which introduces the risk of the child developing electrolyte imbalances, metabolic acidosis, megaloblastic anemia, a host of allergic reactions. In many cultures in the West, humans continue to consume milk beyond infancy, using the milk of other mammals as a food product; the ability to digest milk was limited to children as adults did not produce lactase, an enzyme necessary for digesting the lactose in milk. People therefore converted milk to curd and other products to reduce the levels of lactose. Thousands of years ago, a chance mutation spread in human populations in Europe that enabled the production of lactase in adulthood; this mutation allowed milk to be used as a new source of nutrition which could sustain populations when other food sources failed. Milk is processed into a variety of products such as cream, yogurt, ice cream, cheese.
Modern industrial processes use milk to produce casein, whey protein, condensed milk, powdered milk, many other food-additives and industrial products. Whole milk and cream have high levels of saturated fat; the sugar lactose is found only in milk, forsythia flowers, a few tropical shrubs. The enzyme needed to digest lactose, reaches its highest levels in the human small intestine after birth and begins a slow decline unless milk is consumed regularly; those groups who do continue to tolerate milk, however have exercised great creativity in using the milk of domesticated ungulates, not only of cattle, but sheep, yaks, water buffalo, horses and camels. India is buffalo milk in the world. In food use, from 1961, the term milk has been defined under Codex Alimentarius standards as: "the normal mammary secretion of milking animals obtained from one or more milkings without either addition to it or extraction from it, intended for consumption as liquid milk or for further processing." The term dairy relates to animal milk production.
A substance secreted by pigeons to feed their young is called "crop milk" and bears some resemblance to mammalian milk, although it is not consumed as a milk substitute. The definition above precludes non-animal products which resemble dairy milk in color and texture, such as almond milk, coconut milk, rice milk, soy milk. In English, the word "milk" has been used to refer to "milk-like plant juices" since 1200 AD. In the USA, milk alternatives now command 13% of the "milk" market, leading the US dairy industry to attempt, multiple times, to sue producers of dairy milk alternatives, to have the name "milk" limited to animal milk, so far without success; the mammary gland is thought to have derived from apocrine skin glands. It has been suggested. Much of the argument is based on monotremes; the original adaptive significance of milk secretions may have been nutrition or immunological protection. This secretion became more copious and accrued nutritional complexity over evolutionary time. Tritylodontid cynodonts seem to have displayed lactation, based on
Monocalcium phosphate is an inorganic compound with the chemical formula Ca2. It is found as the monohydrate, Ca2·H2O. Both salts are colourless solids, they are used as superphosphate fertilizers and are popular leavening agents. Material of high purity, as required for baking, is produced by treating calcium hydroxide with phosphoric acid: Ca2 + 2 H3PO4 → Ca2 + 2 H2OSamples of Ca2 tend to convert to dicalcium phosphate: Ca2 → Ca + H3PO4 Superphosphate fertilizers are produced by treatment of "phosphate rock" with acids. Using phosphoric acid, fluorapatite is converted to Ca2: Ca53F + 7 H3PO4 → 5 Ca2 + HFThis solid is called triple superphosphate. Several million tons are produced annually for use as fertilizers. Residual HF reacts with silicate minerals co-mingled with the phosphate ores to produce hexafluorosilicic acid; the majority of the hexafluorosilicic acid is converted to aluminium fluoride and cryolite for the processing of aluminium. These materials are central to the conversion of aluminium ore into aluminium metal.
When sulfuric acid is used, the product is called single superphosphate. Calcium dihydrogen phosphate is used in the food industry as a leavening agent, i.e. to cause baked goods to rise. Because it is acidic, when combined with an alkali ingredient sodium bicarbonate or potassium bicarbonate, it reacts to produce carbon dioxide and a salt. Outward pressure of the carbon dioxide gas causes the rising effect; when combined in a ready-made baking powder, the acid and alkali ingredients are included in the right proportions such that they will neutralize each other and not affect the overall pH of the product. AMCP and MCP are fast releasing most carbon dioxide within minutes of mixing, it is popularly used in pancake mixes. In double acting baking powders, MCP is combined with the slow acting acid sodium acid pyrophosphate. Dicalcium phosphate Havlin, J. L. J. D. Beaton, S. L. Tisdale, W. L. Nelson. 2005. Soil Fertility and Fertilizers. 7th edn. Pearson Prentice Hall, N. J. ISBN 0130278246
The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium; the melting point of a substance depends on pressure and is specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point; because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point. For most substances and freezing points are equal. For example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures.
For example, agar melts at 85 °C and solidifies from 31 °C. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances, the freezing point of water is not always the same as the melting point. In the absence of nucleators water can exist as a supercooled liquid down to −48.3 °C before freezing. The chemical element with the highest melting point is tungsten, at 3,414 °C; the often-cited carbon does not melt at ambient pressure but sublimes at about 3,726.85 °C. Tantalum hafnium carbide is a refractory compound with a high melting point of 4215 K. At the other end of the scale, helium does not freeze at all at normal pressure at temperatures arbitrarily close to absolute zero. Many laboratory techniques exist for the determination of melting points. A Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip, revealing its thermal behaviour at the temperature at that point. Differential scanning calorimetry gives information on melting point together with its enthalpy of fusion.
A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window and a simple magnifier. The several grains of a solid are placed in a thin glass tube and immersed in the oil bath; the oil bath is heated and with the aid of the magnifier melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, optical detection is automated; the measurement can be made continuously with an operating process. For instance, oil refineries measure the freeze point of diesel fuel online, meaning that the sample is taken from the process and measured automatically; this allows for more frequent measurements as the sample does not have to be manually collected and taken to a remote laboratory. For refractory materials the high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees.
The spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source, calibrated as a function of temperature. In this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer. For temperatures above the calibration range of the source, an extrapolation technique must be employed; this extrapolation is accomplished by using Planck's law of radiation. The constants in this equation are not known with sufficient accuracy, causing errors in the extrapolation to become larger at higher temperatures. However, standard techniques have been developed to perform this extrapolation. Consider the case of using gold as the source. In this technique, the current through the filament of the pyrometer is adjusted until the light intensity of the filament matches that of a black-body at the melting point of gold.
This establishes the primary calibration temperature and can be expressed in terms of current through the pyrometer lamp. With the same current setting, the pyrometer is sighted on another black-body at a higher temperature. An absorbing medium of known transmission is inserted between this black-body; the temperature of the black-body is adjusted until a match exists between its intensity and that of the pyrometer filament. The true higher temperature of the black-body is determined from Planck's Law; the absorbing medium is removed and the current through the filament is adjusted to match the filament intensity to that of the black-body. This establishes a second calibration point for the pyrometer; this step is repeated to carry the calibration to hi
The chloride ion is the anion Cl−. It is formed when the element chlorine gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts such as sodium chloride are very soluble in water, it is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating fluid in and out of cells. Less the word chloride may form part of the "common" name of chemical compounds in which one or more chlorine atoms are covalently bonded. For example, methyl chloride, with the standard name chloromethane is an organic compound with a covalent C−Cl bond in which the chlorine is not an anion. A chloride ion is much larger than a chlorine atom, 99 pm, respectively; the ion is diamagnetic. In aqueous solution, it is soluble in most cases. In aqueous solution, chloride is bound by the protic end of the water molecules. Sea water contains 1.94% chloride. Some chloride-containing minerals include the chlorides of sodium and magnesium, hydrated MgCl2.
The concentration of chloride in the blood is called serum chloride, this concentration is regulated by the kidneys. A chloride ion is a structural component of e.g. it is present in the amylase enzyme. The chlor-alkali industry is a major consumer of the world's energy budget; this process converts sodium chloride into chlorine and sodium hydroxide, which are used to make many other materials and chemicals. The process involves two parallel reactions: 2 Cl− → Cl2 + 2 e− 2 H2O + 2 e− → H2 + 2 OH− Another major application involving chloride is desalination, which involves the energy intensive removal of chloride salts to give potable water. In the petroleum industry, the chlorides are a monitored constituent of the mud system. An increase of the chlorides in the mud system may be an indication of drilling into a high-pressure saltwater formation, its increase can indicate the poor quality of a target sand. Chloride is a useful and reliable chemical indicator of river / groundwater fecal contamination, as chloride is a non-reactive solute and ubiquitous to sewage & potable water.
Many water regulating companies around the world utilize chloride to check the contamination levels of the rivers and potable water sources. Chloride salts such as sodium chloride are used to preserve food; the presence of chlorides, e.g. in seawater aggravates the conditions for pitting corrosion of most metals by enhancing the formation and growth of the pits through an autocatalytic process. Chloride is an essential electrolyte, trafficking in and out of cells through chloride channels and playing a key role in maintaining cell homeostasis and transmitting action potentials in neurons. Characteristic concentrations of chloride in model organisms are: in both E. coli and budding yeast are 10-200mM, in mammalian cell 5-100mM and in blood plasma 100mM. Chloride can be oxidized but not reduced; the first oxidation, as employed in the chlor-alkali process, is conversion to chlorine gas. Chlorine can be further oxidized to other oxides and oxyanions including hypochlorite, chlorine dioxide and perchlorate.
In terms of its acid–base properties, chloride is a weak base as indicated by the negative value of the pKa of hydrochloric acid. Chloride can be protonated by strong acids, such as sulfuric acid: NaCl + H2SO4 → NaHSO4 + HClIonic chloride salts reaction with other salts to exchange anions; the presence of chloride is detected by its formation of an insoluble silver chloride upon treatment with silver ion: Cl− + Ag+ → AgClThe concentration of chloride in an assay can be determined using a chloridometer, which detects silver ions once all chloride in the assay has precipitated via this reaction. Chlorided silver electrodes are used in ex vivo electrophysiology. An example is table salt, sodium chloride with the chemical formula NaCl. In water, it dissociates into Na Cl − ions. Salts such as calcium chloride, magnesium chloride, potassium chloride have varied uses ranging from medical treatments to cement formation. Calcium chloride is a salt, marketed in pellet form for removing dampness from rooms.
Calcium chloride is used for maintaining unpaved roads and for fortifying roadbases for new construction. In addition, calcium chloride is used as a de-icer, since it is effective in lowering the melting point when applied to ice. Examples of covalently bonded chlorides are phosphorus trichloride, phosphorus pentachloride, thionyl chloride, all three of which are reactive chlorinating reagents that have been used in a laboratory. Chlorine can assume oxidation states of −1, +1, +3, +5, or +7. Several neutral chlorine oxides are known. Halide Renal chloride reabsorption
The density, or more the volumetric mass density, of a substance is its mass per unit volume. The symbol most used for density is ρ, although the Latin letter D can be used. Mathematically, density is defined as mass divided by volume: ρ = m V where ρ is the density, m is the mass, V is the volume. In some cases, density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials have different densities, density may be relevant to buoyancy and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material water.
Thus a relative density less than one means. The density of a material varies with pressure; this variation is small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid; this causes it to rise relative to more dense unheated material. The reciprocal of the density of a substance is called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density. In a well-known but apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.
Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated and compared with the mass. Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!". As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment; the story first appeared in written form in Vitruvius' books of architecture, two centuries after it took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time. From the equation for density, mass density has units of mass divided by volume; as there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use.
The SI unit of kilogram per cubic metre and the cgs unit of gram per cubic centimetre are the most used units for density. One g/cm3 is equal to one thousand kg/m3. One cubic centimetre is equal to one millilitre. In industry, other larger or smaller units of mass and or volume are more practical and US customary units may be used. See below for a list of some of the most common units of density. A number of techniques as well as standards exist for the measurement of density of materials; such techniques include the use of a hydrometer, Hydrostatic balance, immersed body method, air comparison pycnometer, oscillating densitometer, as well as pour and tap. However, each individual method or technique measures different types of density, therefore it is necessary to have an understanding of the type of density being measured as well as the type of material in question; the density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is measured with a scale or balance.
To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object. If the body is not homogeneous its density varies between different regions of the object. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ = d m / d V, where d V is an elementary volume at position r; the mass of the body t