Art. XVIII.—On a means of selecting the most durable Timber.
[Read before the Wellington Philosophical Society, 21st September, 1877.]
The purpose of the present paper is to explain a method by which timber of the greatest utility, from trees of any species, may be determined.
In the selection of timber for constructive purposes the only guide hitherto has been the prevailing vague opinion that the timber of certain trees is durable; experience, however, has often proved that failures take place with some of those species most highly valued, such as totara, (Podocarpus totara). In all such cases the failure has probably resulted from that indiscriminate system which prevails of cutting down every tree within reach, including young immature trees and quickly-grown mature trees on rich alluvial bottoms, which always produce an inferior timber; the use of such inferior timber in wharves, piles of all kinds, or fence stuff, can only result in premature decay.
As a means to enable engineers to determine the value of any timber I propose the adoption of a standard test of weight, based on an average weight determined from at least twenty measured cube specimens of each species, the specimens to be well seasoned, procured from different districts, and grown under different conditions of growth. By comparing specimens of the same cubic bulk of any timber with its own standard, the most durable of that kind may be selected; as it may be accepted as an axiom in the physiology of timber, that the best will possess the closest structure, contain the largest amount of secretions, and consequently will prove the heaviest and most durable.
If, however, our New Zealand timbers in their natural state, and selected by the test of weight, do not come up in durability to the necessary requirements, there is still in reserve the auxiliary means used in other countries, by which inferior timber is made durable, such as charring, or by the infusion of antiseptic fluids into their structure, and it is possible the colony may ere long waken up to the fact that the introduction of such preservatives has been already too long delayed.