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As of 2006, the most precise measurement of R had been obtained by measuring the speed of sound c a (P, T) in argon at the temperature T of the triple point of water at different pressures P, and extrapolating to the zero-pressure limit c a (0, T). The value of R is then obtained from the relation:
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Note that the especially high molar values, as for paraffin, gasoline, water and ammonia, result from calculating specific heats in terms of moles of molecules. If specific heat is expressed per mole of atoms for these substances, none of the constant-volume values exceed, to any large extent, the theoretical Dulong–Petit limit of 25 J⋅mol ...
Argon has approximately the same solubility in water as oxygen and is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, nonflammable and nontoxic as a solid, liquid or gas. [11] Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature.
Indeed, for solid metallic chemical elements at room temperature, atom-molar heat capacities range from about 2.8 R to 3.4 R. Large exceptions at the lower end involve solids composed of relatively low-mass, tightly bonded atoms, such as beryllium (2.0 R, only of 66% of the theoretical value), and diamond (0.735 R, only 24%). Those conditions ...
According to ASHRAE standard 34, the R-number of a chemical refrigerant is assigned systematically according to its molecular structure and has between two and four digits. If there are carbon -carbon multiple bonds , there are four digits in all: the number of these bonds is the first digit and the number of carbon atoms minus one (C-1) is next.
The above definition is the approach used to develop rigorous expressions from equations of state (such as Peng–Robinson), which match experimental values so closely that there is little need to develop a database of ratios or C V values. Values can also be determined through finite-difference approximation.
Adding argon gas increases the efficiency to about R-3. Using low emissivity glass on surface #2 will add another R-value. Properly designed triple-glazed IGUs with low emissivity coatings on surfaces #2 and #4 and filled with argon gas in the cavities. Certain multi-chambered IG units result in R-values as high as R-24.