FoR.) (STELLENBOSCH)t SUMMARY Part I describes the relative effect of 3·0 per cznr sulphuric acid on six timbers. These were tested by the following combina.tion of methods at atmospheric tempeuuuie:-sla. Determination of hardness and lb. cTILshing strength in comparison with unexposed control timbers and with control specimens immersed in water. La. Q:wntity of sulphuric acid a!Jsorbed and 2b the rate of absorption. 3. Temporary and permanent expansion or shrinkage. 4. Loss of weight of timbers after four weeks' exposure. 5. Colour imparted by the timber to acid, and the condition of the test pieces after immersion and drying. In these tests Balau gave the best iesuus from nearly all aspects j South African Pine was the least satisfactory. For four out of the seven tests Balau, Merbau and Pitch Pine are amongst the three best, and for six out of seven tests they are a'l1Jngst th~first four. N J WJJd t~std beh1.:;;d similar to C.Jlifomian RedwJJd in all respects. O?30MMING Deel I beskrywe die relatieuie uitwerhing van 3·0 pzrsen: swaelsaur op ses iunusootte wat deu: die volgende kombinasie van metodes by atmJSferiese temperatuur getoets is:-la. Bepaling van hardheid en lb. drukvastheid in vergelyking met nie-blootgestelde kontrole monsters en met kontroles in water gedompel. 2a. Hoeveelheid swaelsuur geabsorbeer en 2b. die snelheid daarvan. 3. Tydelike en permanente uitsetting of krimping. 4. Gewigsverlies van die hout na vier weke se blootstelling. 5. Verkleuring van die suur deur die hout en die toestand van die toetsmonsters na onderdompeling en droging. * Senior Chemist, Transvaal and Orange Free State Chamber of Mines Timber Research Laboratory, Johannesburg. t Timber Mechanics Officer, Forest Research In stitute, Pretoria. c Downloaded by [University of California, San Diego] at 12:25 29 June 2016 8 THE SOUTH AFRICAN FORESTRY ASSOCIATION In hierdie toetse het Balau in alle opsigte die beste resuuate gelewer; terwyl Suid-Afrikaanse Den die swakste vertoon het. Vir vier uit die sewe toetse is Balau, Merbau en Harsden tussen die drie beste, en vir ses uit die sewe is hul tussen die eerste vier. Qeen houtsoort wat getoets is, het in aue opsigte met Kaliforniese Rooihout vcrgelyk.

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The chief causes of deterioration in building timbers in South Africa, and the suitability of treated timber in structures, are discussed.The work being done in the Timber Research Unit to evaluate the durability of wood-base board products used as external cladding for buildings is described and the conditions necessary for satisfactory service are outlined.

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The timber of 24 to 26 year old Pinus caribaea var. caribaea and var. hondurensis trees grown in South Africa is studied especially in regard to resin infiltration, low density, and yields of structural and box timber grades. The results are compared with data for P. elliottii and are discussed in regard to earlier investigations conducted on the timber in South Africa and on the species grown in young Queensland plantations. OPSOMMING WAARNEMINGS OP DIE KWALlTEIT VAN DIE HOUT VAN SUlD-AFRI-KAANSGEKWEEKTE PINUS CARIBAEA VAR. CARIBAEA EN VAR. HONDURENSIS Dic haut van oorn-c van Z-t tot 26 jaar oue Pinus e;a,ribaea ua r . curibacu en oar. Iwndurensis wat in Suid-Afrika gekweek is, is bestudeer ueral met betrekking tot harsinfiltrasie, digtheid en opbrengs van uerskillende grade konstruksie-en kishout. Die resultate word vergelyk met data vir P. elliottii en word bespreek na aanleiding van uroeere ondersoeke wat in Suid-Afrika gedoen is asook op soorte wat in jong plantasies in Queensland gekweek is.