PRESERVATION OF TIMBER. 349 



the timber gates from the attacks of the worm, and for the 

 same purpose large scupper-nails are used to protect the fenders 

 and other timbers. 1 



For protecting the piles of a jetty at Port Darwin, Mr. 

 J. W. James sheathed all, up to high- water line, with Muntz 

 metal. 2 



The chemical processes for the preservation of wood are 

 numerous ; the principal and most valuable are the following : 



Corrosive Sublimate, or bi-chloride of mercury under the name 

 of " kyanizing," has met with a considerable amount of success 

 in dry or comparatively dry situations, but in water, and par- 

 ticularly sea water, as a remedy against the marine worm, it 

 has invariably failed. 8 It has been found that piles, after three 

 years' immersion, did not contain a trace of the preservative 

 compound. 



Sulphate of Copper is useful as a preservation against dry 

 rot, and has perhaps been the most successful of all the metallic 

 salts as an antiseptic for timber; 4 but for piers and other 

 structures, exposed to the action of water, it has practically 

 no value, as the water dissolves out the salt with great rapidity. 

 Timber, prepared with this salt, used for marine purposes is 

 as readily destroyed by marine worms as unprepared timber. 



Chloride of Zinc is a powerful antiseptic, but its weak point 

 for wood preserving consists in its extreme solubility in water. 5 

 The timbers most resistant of decay, whether when immersed 

 in water or buried in the ground, are those which are richest 

 in tannic and gallic acid, such as the oak. Hatzfield's process 

 of preservation, therefore, consists in the impregnation of timber 

 of various kinds with tannic acid, followed by an injection of a 

 solution of pyrolignite of iron which in the cells gradually 

 becomes tannin of iron. 6 



Creosote, a distillate from coal-tar, is the only substance 

 which, efficiently applied, accomplishes the object aimed at, 

 namely, the preservation of timber against rot and against the 

 ravages of marine worms. 



True creosote is the product of the destructive distillation 

 of wood, and has never been used for preserving timber ; but 

 a substance having been discovered in coal-tar, since called 



1 M.r.I.C.E., vol. lv. p. 373. 2 Ibid., vol. ciii. p. 337. 



Hid, vol. Ixxviii. p. 102. Hid. * Ibid., 103. 



6 Ibid., vol. xliv. p. 322. 



