IMPREGNATION METHODS 73 



difficult to inject lieartwood ; and it is vastly easier to force liquids 

 through wood tangentially than radially. 



An improvement on any painting process is to submerge the 

 timber in a bath of the preservative, which may be tar, sulphate 

 of iron, copper, zinc, lime, or magnesia, chloride of zinc, borax, 

 creosote, or sugar, and in these processes the replacement of the air 

 and sap in the wood by the liquid wiU generally be hastened by 

 heat. Penetration is, however, slight, and long submergence 

 renders the timber brittle. 



The main desiderata in a preservative are that it should be 

 antiseptic or incapable of supporting fungal life, easily injected, 

 but remaining in the wood when injected, and cheap. 



Of the materials employed for impregnating timber, the most 

 effective is corrosive sublimate (mercuric chloride), the use of which 

 is known, from its inventor, Kyan (1832), as kyanizing. It forms 

 insoluble compounds in the wood, and is, therefore, permanent, 

 except in sea-water ; but its costliness and dangerously poisonous 

 character are against it. Zinc chloride, mainly introduced by Sir 

 WilHam Burnett in 1838, is cheap and effective against both insects 

 and fungi, but less so than creosote. It is claimed that, in Bur- 

 nettizing, as the process is termed, the salt enters into a perma- 

 nent chemical combination with the fibre of the wood, and, without 

 discolouring it, renders it proof against mould and termites, and 

 less flammable ; that wood may be treated when green ; that it 

 win not corrode nails embedded in it ; and that it will take paint or 

 varnish. Copper sulphate, sometimes used for sleepers in Prance, 

 is cheap ; but is deposited in crystals in the wood, rendering it 

 briftle, and, owing to its solubility, is as easily washed out as it is 

 injected. In the Hasselman or Xylosote process a compound 

 solution of iron and copper sulphates and kainite (potassium and 

 magnesium sulphate and chloride) is employed. Creosote, originally 

 suggested by Bethell in 1838, and now very largely employed in 

 various ways, is cheap, lasting in its effects, and useful in rendering 

 the wood damp-proof. The more expensive carboHc acid and ferric 

 tannate have also been used. 



To force the antiseptic solution into the wood, M. Boucherie, 

 who first employed copper sulphate, proposed placing it in an 

 elevated reservoir connected by a pipe with the lower end of a log ; 

 but this requires the log to have its bark on, and is thus a wasteful 

 process. 



A more complicated and costly, but very successful, process 

 consists in the use of air-tight chambers, in which the converted 

 timber is placed. The air is then partially exhausted, so as to 

 draw out some of that in the vessels of the wood, and the anti- 



