The tests have proved con-clusively that copper and mercuric naphthenates are efficient wood preservatives, the stronger the solution the more efficient the preservative effect. A 20 percent solution of copper naphthenate dissolved in gas oil may render white pine, a wood extremely susceptible to attack by termites and fungus, resistant for over 16 years. It would appear from the results of this experiment that toxicity towards termites and fungus is a property of the copper or mercuric ion rather than of the naphthenic radicle which serves primarily as a water-proof carrier and prevents the metal ions from being leached out of the wood by water. Gas oil alone will preserve white pine for up to seven years and this is probably due to the naphthenic acids contained in it. However, gas oil alone cannot be considered an efficient preservative.