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APPENDIX II 



MECHANICAL TESTS OF NATAL WOODS. 



A number of experimental tests have been made in connection with the examination 

 of the principal and other Natal woods. Through the courtesy of the Hon. D. Hunter, 

 General Manager of Railways, and the co-operation of Messrs. W. Milne, Locomotive 

 Superintendent, and W. Butterton, District Engineer of Maintenance, I was enabled to 

 make use, for this purpose, of the testing appliances in the Railway workshops at 

 Durban. 



The experiments are not so complete as I should have desired. Many of the woods 

 collected could not be identified from the foliage alone ; others were excluded as belong- 

 ing to new or doubtful species ; and some that had been left with collectors were not 

 received in time for use. Nevertheless, the tests include nearly all the Natal woods of the 

 first importance, and may prove useful for reference. 



Mr. W. Bazley, of Port Shepstone, kindly made at my request a collection of Coast 

 woods which, unfortunately, could not be fully utilised because the specimens of 

 foliage that had been collected along with the pieces of wood were lost in transmission, 

 and though duplicates were subsequently received, it became necessary to exclude some 

 woods the determination of which admitted of doubt. 



The surplus material has been cut up for distribution in pieces of a convenient size, 

 of which it is intended to deposit complete sets in the Durban Museum, the Maritzburg 

 Museum, and the South African Museum in Capetown. 



The constants required by engineers in determining the resistance of materials in a 

 structure are as follows : 



1. The density or heaviness. The density is related to the other properties of a 

 wood ; it also gives a near approximation to the relative fuel value, and is in direct pro- 

 portion to the cost of transport. 



2. The hardness or resistance to abrasion related to the cost of working. 



3. Coefficients of elasticity, or resistance to stretching and bending. 



4. Limits of elasticity, beyond which a wood retains a permanent set after the load 

 is removed. 



5. Breaking stresses measuring resistance to rupture, such as those to cross breaking 

 and to crushing. 



These properties, together with the durability, mainly determine the uses that a wood 

 may be put to. Though capable of being expressed numerically, it is not easy to 

 assign the values that the several coefficients should have in a wood used for a definite 

 purpose. Numerical data, however, have been obtained for the principal woods of 

 the world ; they are comparable with those arrived at for the Natal woods, and we may, 

 by inspection of the tables, rank any of our woods with a corresponding known wood tne 

 uses of which have been found out by long experience. 



For this reason, and also for convenience in working, metrical units have been 

 used throughout the experiments. The vast majority of researches on the strength of 

 wood have been made by American, German, and French observers, whose results, some 

 of which are added to the table of averages, would not otherwise be readily comparable. 

 But for general convenience, another table of averages for the Natal woods is given in 

 British measure. 



The exotic timbers for which data are given comprise, in addition to well-known 

 woods, some of the species recommended, in Appendix VII,, for planting in Natal. 



For many applications, lightness in a material is as essential as strength, and in order 

 to show readily how the woods tested combine these qualities, the different species have- 

 been arranged in order of their density in the following tables : 



