Vapor Pressures in Western Hemlock Heartwood During Boiling Under Vacuum in Creosote

Experience has shown that the heartwood of western hemlock compares in treatability with that of coast Douglas-fir and for this reason similar commercial methods of treatment have been adopted for the heartwoods of both species. The sapwood of the two species, however, is not equally receptive. Douglas-fir piling has been successfully pressure treated after conditioning by boiling-under-vacuum in creosote for periods up to 36 hours. However, an application of similar conditioning methods to two western hemlock piles in one charge producted erratic penetrations in the study here reported. Data show that the vapor pressure, or vacuum required to initiate boiling, depends on temperature and moisture content of the wood. An apparatus was designed to indicate the minimum vacuum at which a specimen of known moisture content and temperature starts to boil. Vapor pressures in wood below the fiber saturation point were calculated and curves plotted for temperatures in the range of 120?F to 210?F.

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