Specific gravity of gases

Estimation of the Specific Gravity of Gas.—Although the more determination of the specific gravity of gases is of very little nee as a test of their commercial value —unless the gas is to be used for aeronautic purposes —yet, as it is still much employed by gas engineers, and as such an estimation is occasionally useful for controlling the results of chemical analysis, a method by which such a determination may be made is here subjoined. 

Many references give the specific gravity of gases with reference to air. For example, the specific gravity of carbon dioxide is 1.52 relative to air at the same temperature and pressure. Show that this value is correct as long as the ideal gas equation of state applies. 

The reference substance for liquids and solids is normally water. Thus the specific gravity is the ratio of the density of the substance in question to the density of water. The specific gravity of gases frequently is referred to air, but may be referred to other gases, as discussed in more detail in Chap. 3. Liquid density can be considered to be nearly independent of pressure for most common calculations, but, as indicated in Fig. 1.1 it varies somewhat with temperature therefore, to be very precise when referring to specific gravity, state the temperature at which each density is chosen. Thus... 

Gases and Vapoks.— The specific gravities of gases ami vapors are of great importance in theoretical chemistry, as from them we can determine molecular weights, in obedience to the law of Avogadro (p. 14). 

Many process industries use special scales of fluid density, which are usually referred to as gravities. Some are the American Petroleum Institute (API) gravity for oil and petroleum products (Prob. 1.5), Brix gravity for the sugar industry, and Baume gravity for sulfuric acid. Each scale is directly convertible to density, and conversion tables and formulas are widely available. Specific gravities of gases also are used they are based on the density of air at 1 atm and a specific temperature (usually 4 C, sometimes 60 or 70 F). 

In a paper read 12 November 1802, Dalton took for the specific gravities of gases ... 

The reference most commonly used for solids and liquids is water at its maximum density, which occurs at 4°C this reference density is 1.000 g/cm, 1000 kg/m, or 62.43 Ib/ft. Note that, since the specific gravity is a ratio of two densities, it is dimensionless. Therefore, any set of units may be employed for the two densities as long as they are consistent. The specific gravity of gases is used only rarely when it is, air at the same conditions of temperature and pressure as the gas is usually employed as the reference substance. 

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