This International Standard specifies a method for the determination of the aniline point of petroleum products and hydrocarbon solvents, and the mixed aniline point of those products having aniline points below the temperature at which aniline will crystallize from the aniline-sample mixture. Method 1 describes a procedure for transparent samples with an initial boiling point above ambient temperature, and for those with an aniline point below the bubble point and above the solidification point of the aniline-sample mixture. Method 2, a thin film method, describes a procedure for samples too dark for testing by method 1. Methods 3 and 4 are for samples that may vaporize appreciably at the aniline point. NOTE 1 Method 4 is particularly suitable where only small quantities of sample are available. Method 5 describes a procedure using automated or automatic apparatus suitable for the range covered by methods 1 and 2. NOTE 2 The aniline point (or mixed aniline point) is useful as an aid in the characterization of pure hydrocarbons and in the analysis of hydrocarbon mixtures. Aromatic hydrocarbons exhibit the lowest values and paraffins the highest, with cycloparaffins and olefins exhibiting intermediate values. In a homologous series, the aniline points increase with increasing molecular mass. NOTE 3 Although the aniline point can be used in combination with other physical properties in correlative methods for hydrocarbon analysis, the most frequent usage is to provide an estimate of the aromatic content (or “aromaticity”) of hydrocarbon mixtures.