1.1 本试验方法包括测定纯液体的蒸汽压，即在40℃下由封闭容器中的混合物施加的蒸汽压 %±5 %以及纯液体和混合液体的初始热分解温度。它适用于与硼硅酸盐玻璃相容且蒸汽压在133之间的液体 Pa（1.0 torr）和101.3 kPa（760 torr）。该测试方法适用于从环境温度到623 K.温度范围可以扩展到包括低于环境温度的温度，前提是使用用于这种温度的合适的恒温浴。 注1: 等渗仪是一种定容仪器，用它在非纯液体上获得的结果与恒压蒸馏中获得的结果不同。 1.2 大多数石油产品在相当宽的温度范围内沸腾，这一事实应在讨论其蒸汽压时得到承认。即使是遵循拉乌尔定律的理想混合物，随着较轻组分的去除，蒸汽压也会逐渐降低，这在复杂的混合物中尤其突出，例如含有微量脱蜡溶剂的润滑油等。这种混合物在封闭容器中很可能施加高达其平均组成计算的100倍的压力，它是一个封闭的容器，由同位素仪模拟。用于测量开放系统中的表观蒸汽压的试验方法 D2878 ，建议使用。 1.3 以国际单位制表示的数值应视为标准。SI单位后括号中给出的值仅供参考，不被视为标准值。 1.4 警告 --汞已被许多监管机构指定为一种可能导致严重医疗问题的危险物质。汞或其蒸汽已被证明对健康有害，对材料具有腐蚀性。处理汞和含汞产品时要小心。有关更多信息，请参阅适用的产品安全数据表（SDS）。当地或国家法律有可能禁止销售汞或含汞产品，或两者兼而有之。用户必须确定在其所在地销售的合法性。 1.5 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 有关具体的警告语句，请参阅 6.10 ， 6.12 和 附件A2 。 1.6 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 ====意义和用途====== 5.1 通过同位素法测定的物质的蒸汽压反映了所接收样品的性质，包括大多数挥发性成分，但不包括溶解的固定气体，如空气。蒸汽压力， 本身 ，是一种热力学性质，仅取决于稳定系统的组成和温度。同位素法设计用于最大限度地减少测量过程中可能发生的成分变化。

1.1 This test method covers the determination of the vapor pressure of pure liquids, the vapor pressure exerted by mixtures in a closed vessel at 40 % ± 5 % ullage, and the initial thermal decomposition temperature of pure and mixed liquids. It is applicable to liquids that are compatible with borosilicate glass and that have a vapor pressure between 133 Pa (1.0 torr) and 101.3 kPa (760 torr) at the selected test temperatures. The test method is suitable for use over the range from ambient to 623 K. The temperature range may be extended to include temperatures below ambient provided a suitable constant-temperature bath for such temperatures is used. Note 1: The isoteniscope is a constant-volume apparatus and results obtained with it on other than pure liquids differ from those obtained in a constant-pressure distillation. 1.2 Most petroleum products boil over a fairly wide temperature range, and this fact shall be recognized in discussion of their vapor pressures. Even an ideal mixture following Raoult's law will show a progressive decrease in vapor pressure as the lighter component is removed, and this is vastly accentuated in complex mixtures such as lubricating oils containing traces of dewaxing solvents, etc. Such a mixture may well exert a pressure in a closed vessel of as much as 100 times that calculated from its average composition, and it is the closed vessel which is simulated by the isoteniscope. For measurement of the apparent vapor pressure in open systems, Test Method D2878 , is recommended. 1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard. 1.4 WARNING —Mercury has been designated by many regulatory agencies as a hazardous substance that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use caution when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their location. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see 6.10 , 6.12 , and Annex A2 . 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 The vapor pressure of a substance as determined by isoteniscope reflects a property of the sample as received including most volatile components, but excluding dissolved fixed gases such as air. Vapor pressure, per se , is a thermodynamic property which is dependent only upon composition and temperature for stable systems. The isoteniscope method is designed to minimize composition changes which may occur during the course of measurement.