116 PROPERTIES OF WOOD. 



bleached by calcium-chloride or by hydrogen-peroxide. Species 

 of wood that are poor in tannin and resin, such as soft broad- 

 leaved woods, are best for the purpose. It is more difficult to 

 bleach the wood of conifers and oaks. Holly, hornbeam, and 

 horse-chestnut are naturally the whitest of European woods. 



e. Wood- staining. 



All softwoods are more easily stained than are heartwoods, 

 as the dye penetrates more deeply into their tissues. Woods 

 with numerous small vessels are more suitable for staining 

 than those with a few large vessels, while coniferous woods 

 having no vessels are not so suitable. Woods with fine 

 medullary rays are much preferred to those with large 

 rays. Lime, pear, birch and maple are most suitable; then 

 ash, oak, hornbeam and beech ; worst of all, conifers. 



/. Pyroyra-ithy. 



Pyrography, or poker-work, is the art of burning designs 

 into wood with a red-hot platinum stylus, the design having 

 been previously drawn with a lead-pencil on the wood and its 

 lines then followed with the stylus. Evengrained wood of 

 Cembran pine, beech, lime, maple, and pale oakwood are used. 



(/. Suitability of Wood for Charcoal-making. 



Soft broadleaved and coniferous woods are charred more 

 easily than hard and heavy woods. Branches are more 

 difficult to char than stem-wood and the latter than root- 

 wood; water in wood is an obstacle to charring. Unsound 

 wood and wood cut into small pieces is charred easily. The 

 loss of volume in charring heavy woods is about 45 per cent, 

 and for light woods about 30 per cent. ; in all woods there is a 

 loss of weight, in conversion to charcoal, of 75-80 per cent., only 

 20 to 25 per cent, of the weight of the wood remaining as char- 

 coal. Charcoal from hard, heavy woods has always a greater 

 heating-power than that of soft woods, so that a scale of the 

 best woods for charcoal-making is prepared easily. 



k. Aptitude of Wood for l>ni>rcijnatiun. 



Wood is impregnated in order to increase its durability. 

 Woods resist {superficial impregnation by liquids, as they do 



