(i(;2 AN'IISKI'TIC TKKATMENT UF TlMIiEll. 



foniiinj^' with tlio ^^liie a leathery substance which fills the pores of 

 the wood and pifvonts tlie washing' out of the zinc chloride. — Tu.] 



The use of chloride of mercury (corrosive sublimate) was 

 patented in 1832 by the Eu<,flishman Kyan as u preservative for 

 tinibt-r. 



[Kyanising \\as for some time extensively used in Britain, and is 

 useful iu dr}' situations but useless in sea-water ; coiTosive sublimate 

 being a strong poison has also the drawback of injuring the workmen 

 \vlii> are employed in handling it, it also corrodes iron and is some- 

 what volatile at ordinary temperatures. 



Products from the distillation of coal or wood containing more or 

 less heavy tar-oils, carbolic acid, tar, acetic acid, »\:c., are chiefly used 

 in the form of heavy tar-oils from coal-tar, the process being intro- 

 duced by Bethell, in 1838, and subsequently termed creosoting, 

 though there is no true creosote in coal-tar. The coal-tar is 

 obtained as a residual product of gas-works and is distilled by being 

 suV)jected to the heat of a furnace, yielding certain oils lighter than 

 water (naplithas), oils heavier than water, and pitch, which runs out 

 from the bottom of the still and solidities into a hard black substance- 

 Formerly the heavy oils were used without further distillation for 

 preserving tindjer, but Boulton considers that the tar acids (including 

 carbolic acid) which they contain, are speedily washed out of injected 

 timber and that the heavier portion of the oils which clogs up wood- 

 pores is more valuable than carbolic acid as a preservative of timber. 

 It is essential that wood should be air-dried before being creosoted, 

 the method by which this is secured will be described further on. 

 Wood-tar is less used than coal-tar, though it is undoubtedly 

 superior to it for injecting timber, the main difficulty witli coal-tar 

 being its viscosity and the consequent difficulty of driving it deeply 

 into wood. Boulton maintains that Newcastle coal produces heavier 

 oils than other Knglish or Scotch coal and that the lighter country 

 or Scotch oils ])enetrate more deeply into timber but do not produce 

 such a lasting effect as the heavier London oil from Newcastle coal. 

 -Tu.] 



Creosoting is cbielly employed in Britain and is now being 

 increasingly used in France, Germany and other countries ; 

 although the method of injection now employed is capable of 

 imi)rovenu'nt, it is undoubtedly superior to injection by any 

 metallic salts. Creosoted wood is bard, tough and black, 

 much less absorptive of moisture than uncreosoted wood and 



