NATURE 



81 



THURSDAY, APRIL .3, 1919. 



PRESERVATION OF TIMBER IN INDIA. 



The Indian Forest Records. Vol. vi., part iv. : 

 "A Further Note on the Antiseptic Treatment 

 of Timber, recording Results obtained from Past 

 Experiments." By R. S. Pearson. Pp. vi + ii + 

 128 + maps and plates. (Calcutta: Superinten- 

 dent Government Printing-, India, 1918.) 

 Price 3 rupees, or 45, 6d. 



A LTHOUGH the main principles involved in 

 -^ the antiseptic treatment of timber as a 

 means of protecting- it against decay induced by 

 fungi are invariable, their precise application is 

 necessarily modified in detail with differences of 

 climate and of the timbers treated. In India an 

 additional factor intervenes in the necessity for 

 the simultaneous protection of wood from attacks 

 by insects, and from termites in particular. 



Extremes of climate in India introduce diffi- 

 culties in the antiseptic protection of timber that 

 are lacking in cold-temperate regions. For in- 

 stance, as Mr. Pearson notes, in hot, dry Indian 

 districts the highly antiseptic lighter oils of raw 

 creosote evaporate more rapidly than in cooler 

 regions, so that ordinary creosote-oil would appear 

 to be not so well suited for the preservation of 

 railway sleepers in India as in England ; accord- 

 ingly Mr. Pearson, with the support of pre- 

 liminary trials, rather favours the usage of 

 heavier tar-oils. This relatively rapid loss of the 

 more volatile tar-oils suggests that in India there 

 should be deeper penetration, or possibly injection 

 of larger quantities, of tar-oils when compared 

 with current European practice ; yet it is quite 

 possible that the heavier oils remaining in the 

 wood may be more toxic at the higher tempera- 

 tures in India than in Europe, in which case 

 ordinary creosote-oils might be well suited for 

 use in India. 



Depth and evenness of penetration of the anti- 

 septic, and the amount of this injected, may thus 

 acquire increased importance in India. But these 

 details in the impregnation of timber, when pneu- 

 matic pressure is employed, are determined not 

 only by the nature and water-contents of the 

 wood, but also by the temperatures at which the 

 process is carried out, by the intensity, dura- 

 tion, and rate of application of the pneumatic 

 pressure, and even by the gas-pressures prevail- 

 ing in the injection vessel before the admission 

 or after the expulsion of the antiseptic. Onfy the 

 fringe of this branch of the subject as regards 

 Indian woods has been touched. The modern 

 experiments we owe to Mr. Pearson, who con- 

 ducted trials under varying conditions on the 

 penetration of green oil mixed with "earth oil" 

 ("liquid fuel ") into some dipterocarp and 

 several other timbers. In an earlier paper Mr. 

 Pearson described his experiments on the absorp- 

 tion of antiseptic solutions by a number of Indian 

 timbers treated in hot or cold baths ("open 

 tanks "). 



NO. 2579, VOL. 103] 



Quite apart from any weakening of the anti- 

 septic by evaporation of its components, depth 

 of penetration is of special importance where the 

 climate is hot and dry for prolonged periods and 

 the treated wood is used out of doors — for in- 

 stance, in the form of railway sleepers. In such 

 places during drought the wood is particularly 

 prone to develop splits, which not only cause 

 mechanical weakness, but also provide points of 

 entry for destructive fungi or insects. Mr. Pearson 

 directs particular attention to this danger of 

 splitting, and to the consequent necessity for 

 seasoning wood to such a degree of dryness as 

 will correspond with the atmospheric humidity. He 

 suggests the possible use of artificial seasoning 

 (kiln-drying) when a considerable degree of dry- 

 ness has to be attained. In this connection several 

 difficulties call for investigation. It will probably 

 be found that in very dry parts of India the wood 

 is in moisture-equilibrium with the air when it 

 contains as little as 6, or even less, per cent, of 

 water; but under artificial seasoning to such a 

 degree of dryness wood is apt to become brittle. 

 Again, the question arises as to the course to be 

 pursued when the climate includes sharply marked 

 alternating hot dry and wet seasons. Both these 

 difficult cases may perhaps be met more or less 

 efficiently by using a sufficiently deep injection 

 of solutions (say of tar-oils) that obstruct the 

 interchange of moisture between wood and atmo- 

 sphere, and consequently decrease warping and 

 splitting. 



When the climate is permanently or periodically 

 humid, soluble salt solutions, such as zinc chloride, 

 will be washed out of exp>osed wood even more 

 rapidly than in this country ; accordingly, Mr. 

 Pearson tentatively concludes that such preserva- 

 tive salts are unsuitable for use in sleepers in 

 wet Indian climates. It appears possible that the 

 use of zinc chloride to preserve railway sleepers 

 in hot, dry climates may likewise be unsatisfac- 

 tory ; for the dry sleepers, exposed to the direct 

 rays of the sun, will be raised to temperatures that 

 may be sufficiently high to cause the zinc chloride to 

 exercise its directly destructive action on the wood. 



It is clear that, in general, but particularly in 

 extreme Indian climates, in selecting an antiseptic 

 solution as a preservative of timber, it is impos- 

 j sible to rely merely upon the fungicidal or insecti- 

 cidal efficiency of the fresh solution. Only pro- 

 longed trials can solve the problems as to the 

 depth of penetration and the amount of solution 

 that yield most satisfactory economic results. The 

 antiseptic most commonly used in England for 

 railway sleepers and paving blocks, "creosote- 

 oil." is costly in India, where its antiseptic dura- 

 bility is also dubious. Accordingly, Mr. Pearson's 

 experiments include trials with solutions ranging 

 from various tar-oils and their derivatives to rock- 

 oils, salt solutions (including zinc chloride and 

 sodium fluoride), and mixtures of these, also a 

 saccharine solution containing arsenic in solution. 



To determine all the unknown factors that will 

 form the bases of the technically and commercially 

 most satisfactory methods of preserving various 



F 



