Determination of the mass of a sample and expressing its value in units, fractions, and multiples of the mass of the prototype of the international kilogram.

Related Terms


A term construed to mean a representative sample of the circulating boiler water, after generated steam has been separated and before the incoming feedwater or added chemical becomes mixed with it so that its composition is affected. (ASTM - D860)


The transfer of heat or mass by large-scale fluid movements. When the process occurs, due to density and temperature differences, it is termed natural convection. When the process occurs due to external devices (such as fans), it is termed forced convection.


The mass per unit volume of a substance at specified conditions of temperature and pressure.


The volume occupied by one molecular mass in grams (g mole) under specific conditions. For an ideal gas at standard temperature and pressure it is 0.0224 m3/g mole.


The amount of substance. Mass that is numerically equal to the molecular mass. It is most frequently expressed as the gram molecular mass (g mole) but may also be expressed in other mass units, such as the kg mole. At the same pressure and temperature the volume of one mole is the same for all ideal gases. It is practical to assume that petroleum gases are ideal gases.


The mass of a liquid at a given temperature compared with the mass of an equal volume of fresh water at the same temperature or at a different given temperature.


The mass of a vapor compared with the mass of an equal volume of air, both at standard conditions of temperature and pressure.

SI (Systeme International) Units

An internationally accepted system of units modeled on the metric system consisting of units of length (meter), mass (kilogram), time (second), electric current (ampere), temperature (degrees Kelvin), and amount of substance (mole).


A vapor sample of known composition and concentration used to calibrate gas detection equipment.


The process whereby a volume of liquid is converted into a multiplicity of small drops. The principal goal is to produce a high surface area to mass ratio so that the liquid will vaporize quickly and thus be susceptible to combustion.

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