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Fluorescein aqueous solutions, diluted from 10 000 to 1 part per million in intervals of ten-fold dilution. At 10 000 ppm the solution is a deep red colour. As the concentration decreases the colour becomes orange, then a vibrant yellow, with the final 1 ppm sample a very pale yellow.
For example, such a regulation might limit the concentration of NOx to 55 ppmv in a dry combustion exhaust gas corrected to 3 volume percent O 2. As another example, a regulation might limit the concentration of particulate matter to 0.1 grain per standard cubic foot (i.e., scf) of dry exhaust gas corrected to 12 volume percent CO 2.
In the metric system, a microgram or microgramme is a unit of mass equal to one millionth (1 × 10 −6) of a gram. The unit symbol is μg according to the International System of Units (SI); the recommended symbol in the United States and United Kingdom when communicating medical information is mcg .
Raoult's law (/ ˈ r ɑː uː l z / law) is a relation of physical chemistry, with implications in thermodynamics.Proposed by French chemist François-Marie Raoult in 1887, [1] [2] it states that the partial pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component (liquid or solid) multiplied by its mole fraction in the mixture.
[14] [15] Otherwise, water hardness is measured in the dimensionless unit of parts per million (ppm), numerically equivalent to concentration measured in milligrams per litre. [14] [15] One grain per U.S. gallon is approximately 17.1 ppm. [14] [note 1] Soft water contains 1–4 gpg of calcium carbonate equivalents, while hard water contains 11 ...
In food science, water activity (a w) of a food is the ratio of its vapor pressure to the vapor pressure of water at the same temperature, both taken at equilibrium. [1] Pure water has a water activity of one. Put another way, a w is the equilibrium relative humidity (ERH) expressed as a fraction instead of as a percentage.
For example, IUPAC has, since 1982, defined standard reference conditions as being 0 °C and 100 kPa (1 bar), in contrast to its old standard of 0 °C and 101.325 kPa (1 atm). [2] The new value is the mean atmospheric pressure at an altitude of about 112 metres, which is closer to the worldwide median altitude of human habitation (194 m). [10]
The system can be traced back to the measuring systems of the Hindus [18]: B-9 and the ancient Egyptians, who subdivided the hekat (about 4.8 litres) into parts of 1 ⁄ 2, 1 ⁄ 4, 1 ⁄ 8, 1 ⁄ 16, 1 ⁄ 32, and 1 ⁄ 64 (1 ro, or mouthful, or about 14.5 ml), [19] and the hin similarly down to 1 ⁄ 32 (1 ro) using hieratic notation, [20] as ...