C.—3,

The major kiln-drying unit serviced during the year was the Department's own four-chamber installation at the Waipa State Mill. In the drying of P. radiata the amount of moisture to be evaporated was found to be one and a half times as great as with a green rimu load and the rate of drying of the charge to be almost twice as fast, stressing the necessity for adequate heating and ventilating capacity. Handling of the timber in 16 ft. unit packages (four to the load cross-section) permits rapid assembly and dismantling of kiln charges by means of end-lift and straddle trucks, but makes it extremely difficult to secure as accurate alignment as with ordinary hand-stacked loads. Double dry-bulb control characterizes all four kilns. The pilot kiln, which takes only one load of four unit packages, embodies an interesting feature in that the whole charge can be balanced on a weighbridge and its weight recorded at all stages of the kiln run. It is being used for the experimental drying of both exotic and indigenous timbers. Section E. —Wood Preservation. 89. Close attention has been given to the use of all classes of wood preservatives, and it is the firm policy of the Forest Service to recommend the use of only nonproprietary standard preservatives until such time as the price of proprietary preservatives is reduced to a reasonable level and their conformity to a reasonable standard proven. Three classes of wood-preservatives have to be considered —namely, (a) creosotes, (b) volatile oil preservatives, and (c) water-soluble preservatives. In the first class, non-proprietaiy British Standard Specification creosote alone is recommended and used by the Service. Proprietary creosotes have been promoted from time to time at as much as 12s. 6d. per gallon, whereas the wholesale price of standard creosote is in the vicinity of Is. 6d. per gallon. The use of clean volatile oil preservatives in the treatment of building timbers against insect and fungous attack has increased rapidly in New Zealand, and as a protection against high-priced proprietary products the Forest Service has adopted minimum standards to which at least one non-proprietary preservative—namely, 5 per cent, pentachlorphenol —fully complies and is recognized by the Forest Service as a standard building preservative. The third class —namely, water-soluble preservatives —have a very limited use under New Zealand conditions, with the exception of sapstain-preventive chemicals which are being used in increasing quantities in the protection of freshly-sawn timber. Thus at the State mill at Rotorua 592,000 board feet were chemically treated during the year with highly satisfactory results. Although the chemicals used in these treatments are proprietary products, they have been provisionally accepted as standard preservatives on account of their low and competitive prices (the cost of chemical required to treat 100 board feet of timber is approximately 2d.), of their efficacy under New Zealand conditions, and of their practically universal adoption by milling industries overseas. Laboratory investigational work on wood preservation included development of standard methods of testing preservatives for toxicity, volatility, leach ability, solubility, and penetration ; isolation and study of wood-destroying fungi ; timberdurability tests ; and determinations of evaporation losses in New Zealand, creosotes subjected to commercial temperatures. Progress has been made towards the standardization of priming paints for the resinous and relatively knotty exotic timbers which, it is anticipated, will be used in increasing quantities for building purposes. Aluminium powder in long oil spar varnish has been adopted as a provisional standard, and several exotic-pine cottages at Rotorua have been so treated as commercial tests. Section F. —Derived Products. 90. Fundamental studies into the economics of local pulp and paper manufacture have been continued. Two problems of outstanding importance are under close investigation, one relating to the incidence and control of sapstains and mould on exotic pulpwoods, and the other to the seasonal variation in exotic pulpwood

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