4.1 Vapor pressure is an important specification property of commercial propane, special duty propane, propane/butane mixtures, and commercial butane that assures adequate vaporization, safety, and compatibility with commercial appliances. Relative density, while not a specification criterion, is necessary for determination of filling densities and custody transfer. The motor octane number (MON) is useful in determining the products' suitability as a fuel for internal combustion engines.

1.1 This practice covers, by compositional analysis, the approximate determination of the following physical characteristics of commercial propane, special-duty propane, commercial propane/butane mixtures, and commercial butane (covered by Specification D1835): vapor pressure, relative density, and motor octane number (MON).

1.1.1 This practice is not applicable to any product exceeding specifications for nonvolatile residues. (See Test Method D2158.)

1.1.2 For calculating motor octane number, this practice is applicable only to mixtures containing 20 % or less of propene.

1.1.3 For calculated motor octane number, this practice is based on mixtures containing only components shown in Table 1.

1.2 The values stated in SI units are to be regarded as standard.

1.2.1 Exceptions: 

1.2.1.1 Non-SI units in parentheses are given for information only.

1.2.1.2 Motor octane number and relative density are given in MON numbers and dimensionless units, respectively.