Property data can be difficult to find. In addition to variations of compound names such as we explored last week, the names of the properties of interest often vary over time, properties may be reported in units that are different from those sought, or the conditions vary under which the properties were measured. Data most often appear first in the primary literature, and is then collected into various compilations through a process of evaluation and selection. It is not unusual to find several different values for the same physical property, and the searcher may need to re-visit the original primary sources. During class, we will explore several handbooks available online, including Lange's handbook of chemistry, Perry's chemical engineers' handbook, the webbook from NIST, Beilstein and Gmelin Crossfire, and a variety of other property sources.