The physical constants of kauri gum

Abstract

Kauri Gum is the fossilised resin of the Kauri Tree (Agathis Australis). The tree which often attains great size is found only in the Auckland Province, and the fossil gum is found embedded beneath the surface of the soil in open country on the sites of ancient forests. The gum is located by probing with long spears, and is then dug out. It is largely used in the manufacture of high class varnishes and linoleums. There is a large range of colour - from dark, almost black gum, that has evidently been subject in times gone by to the action of forest fires, to clear white, invaluable for certain descriptions of Varnishes. The pieces collected vary from small "chips" to the size of large flint stones and very occasionally lumps up to 50 lbs are found. Most of the gum obtained to-day is of the chip variety and considerable labour is involved in separating it from its surrounding earth. The gum used in these experiments was cut from a block weighing about three pounds, consisting of the best quality gum. As far as could be ascertained only one previous attempt has been made to determine any of the physical constants of the gum and then not even approximate results were obtained. This research was designed primarily to measure: (1) Resistivity (2) Surface Resistance (3) Dielectric Constant These three are of importance in connection with the possible electrical separation of the chip gum from impurities. Several methods are in use on the gum fields for separating the gum from clay and soils, but none give very good results. Since this research was started an English company has patented an electrostatic method of separation and intends to use it on their gum fields in North Auckland. The Refractive index and Specific Heat of the gum were also measured.