Work on the interrelations of the flammability properties of n-olkanes in air has been extended to both vapor and liquid fuel mixtures. By application of Raoult's and Dalton's laws governing vapor pressure and composition above a solution of two or more liquid hydrocarbons to Le Chatelier's rule governing the flammability limits of vapor mixtures, equations have been derived which make it possible to predict overall flammability properties of mixtures from the properties and proportions of the individual components. The properties which were studied include: lower and upper flammability limits, heat of combustion, stoichiometric concentration, flash point, and flammability index ("explosiveness"). Experimentally determined flash points of multicomponent solutions were in good agreement with the calculated values, confirming the point that hydrocarbon solutions follow the above laws, and also confirming the concept of flash point as that temperature at which the vapor concentration above a liquid is equal to that at its lower flammability limit. The derived equations demonstrate why vapor pressure of individual constituents plays a more important role than concentration on the overall flammability properties of liquid solutions, and that a very small amount of a highly volatile contaminant in a relatively nonflammable fuel may make it flammable.

S P O N T A N E O U S ignition properties of combustible materials, particularly fuels and hydrocarbons, have been an important area of combustion research for over 50 years. This interest in spontaneous ignition is based on the important role which this phenomenon plays in the fire hazard in the handling and storage of combustibles, the performance of various types of combustion engines, and the elucidation of oxidation and combustion mechanisms of fuels, hydrocarbons, and related substances.The spontaneous ignition temperature (SIT) of a substance is defined as that lowest temperature a t which the substance will ignite in air without the aid of a spark or flame. Based on the thermal theory of ignition and on classical reaction-rate theory, spontaneous ignition temperature can be regarded as that temperature to which a combustible mixture must be raised so that the rate of heat evolved by the exothermic oxidation reactions of the system will just overbalance the rate a t which heat is lost to the surroundings. However, the criterion that is usually taken to indicate ignition-i.e., visible and/or audible combustion observed under ordinary laboratory conditions-is quite subjective. Also, the spontaneous ignition temperature of a substance should be a quantity related to some characteristic chemical property of the material, yet its experimentally determined value is markedly dependent on the method and apparatus employed for its determination. I n a recent monograph, Mullins (1 7) reviews this subject, including the importance, definition, and meaning of spontaneous ignition and spontaneous ignition temperature and describes numerous methods for its determination and the factors which influence results.Earlier work on the effects of oxygen concentration ( 2 , 12-14) indicated that it would be of interest to study spontaneous ignition in finer detail using better instrumentation with particular emphasis on preignition behavior. A static system was chosen for its simplicity and to make temperature-time measurements. An inherent fault of such a system is the problem of uniform gas mixing after introducing the hydrocarbon sample. This problem should be minimized by discharging the sample as a fine spray and by a long time delay before ignition occurs.The general purpose of this investigation was to study the influence of chemical structure on the spontaneous ignition processes. Specifically, the influence of chain length, chain branching, unsaturation, and of cyclic and aromatic structures on the preignition processes was examined by measuring internal gas temperature and oxygen consumption.I n addition to minimum ignition temperature in air for cool-or hot-flame ignition, minimum reaction temperature, preignition temperature range, temperature rise, and oxygen consumption a t ignition were useful. A correlation between these values and ease of oxidation and ignition was noted. The findings were as follows: I n general, decreasing chain length, addition of methyl groups, unsaturation, and particularly, chain branchin...

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