Abstract: In the production of petroleum-based products in a refinery, viscosity and density are accurately and repeatedly measured at an elevated temperature, sometimes in a hostile environment. A densitometer and viscometer are located in a non-purged enclosure, but the electrical controls that could cause a spark to ignite fumes are located in a purged enclosure with connections there between. A heat pipe extending from the purged enclosure to the non-purged enclosure accurately controls the temperature of a sample during testing. For difficult to handle petroleum-based products such as asphalt, a sample conditioning system prepares the sample prior to testing.