Mutual solubility data have been determined for seven binary and two ternary nitroethane-hydrocarbon systems using the phase equilibrium and cloud point methods. The hydrocarbons used in the binary studies were: n-hexane, 2-methylpentane, 1 -hexane, n-octane, 2,2,4-trimethylpentane, 1-octene, and n-decane. Mutual solubility data for the binary systems were determined at various temperatures up to the critical solution temperature. The ternary systems studied were nitroethane-noctane at 0 and 25 C. and nitroethane-n-octane-2,2,4-trimethylpentane at 35 C. N ITROPARAFFINS have miscibility characteristics similar to furfural and other organic solvents used in petroleum extraction. The consideration that nitroparaffins might have potential use in the petroleum extraction field initiated this study of phase equilibria. A series of qualitative tests was carried out to ascertain the possible occurrence of partial miscibility in 52 binary nitroparaffinhydrocarbon systems in a temperature range from -15 to 3OoCc. (3). These tests include 13 hydrocarbons (npentane, n-hexane, 2-methylpentane, 1-hexene, cyclohexane, cyclohexene, n-heptane, n-octane, 2,2,4-trimethylpentane, 1-octene, n-decane, benzene, and toluene) and four nitroparaffins (nitromethane, nitroethane, 1-nitropropane, 2-nitropropane). From these tests certain generalities were observed: for a given nitroparaffin, the critical solution temperature increased as the number of carbon atoms in the straight chain saturated aliphatic hydrocarbon increased; for hydrocarbons containing the same number of carbon atoms, the critical solution temperature decreased in the following order: normal paraffin, isomers of normal paraffin, saturated cyclic hydrocarbon, and unsaturated hydrocarbons; for a given hydrocarbon, the critical solution temperature decreased as the number of carbon atoms in the nitroparaffin increased. These generalities suggested that some of the lower nitroparaffins such as nitromethane or nitroethane can be used to separate hydrocarbons of different structure and/or molecular weight. A literature survey revealed a paucity of quantitative mutual solubility data for nitroparaffin-hydrocarbon systems. This article presents mutual solubility data for seven binary and two ternary nitroethane-hydrocarbon systems. The mutual solubility data were determined at various temperature intervals up to the critical solution temperature. The hydrocarbons used in the binary studies (3) were: n-hexane, 2-methylpentane, 1-hexene, n-octane, 2,2,4-trimethylpentane, 1-octene, and n-decane. The ternary systems studied (5) were nitroethane-n-octane-loctene, and nitroethane-n-octane-2,2,4-trimethylpentane. The reader is referred elsewhere (3, 5) for experimental details and further discussion. EXPERIMENTAL Materials. All the hydrocarbons used in this study had a purity of better than 99 mole % as stated by the supplier. This was supported by both refractive index and gas chromatographic analysis. The nitroparaffins were reported by the supplier to be better than 96 mole % pure. The nitromethaneused had a purity of 99 mole %. The nitroethane was reported to contain 3.9% of 2-nitropropane. Analysis of the nitroethane by gas chromatograph confirmed the presence of 2-nitropropane. The materials were used without further purification. Procedure. The data for the binary and ternary mixtures studied weie obtained by the synthetic (cloud-point) and analytical (phase equilibrium) methods as described by Vold and Vold (7). The cloud point was easily detected for the binary systems studied. For the ternary systems the cloud point was determined by titrating a third component into binary samples of known composition in a constant temperature bath. In the case of the two ternary mixtures, no distinct change in the transparency of the clear mixture was observed to indicate to the unaided eye that the cloud point had been obtained; only the presence of finely dispersed globules of the second phase, which were visible through a magnifying glass, denoted the fact that the cloud point had been reached. The analytical method consisted of withdrawing a sample from each of the coexisting phases (for either the binary or ternary mixtures) from an equilibrium cell in a constant temperature bath, and analyzing the samples by gas chromatographic techniques. The temperature of the bath was controlled to f 0.05 C. The commonly used refractive index method of analysis could not be applied to these systems because nitroethane and the hydrocarbons studied do not have a sufficiently large difference in their refractive index values. Analysis of the equilibrium liquid phases was carried out by means of a Model 154B Vapor Fractometer (PerkinElmer Corp., Norwark, Conn.) using helium as the carrier gas. Complete resolution of all binary systems studied,