APTITUDE FOE BEING WORKED. 115 



l>. Ap/i/ittle of Wood for bei/it/ Ground i/ifo Pulp. 



When wood is to be ground into pulp for paper-making, etc., 

 if its transverse section is placed against the rotating stone, 

 the resulting triturated wood is like meal ; if the longitudinal 

 surface be turned to the stone, the ground material is too 

 coarse for paper-making. A suitable length of fibres for 

 paper is produced when the pith of the wood is at an angle of 

 45 to 50 degrees to the rotating stone. Softwoods are easier 

 to grind than hardwoods, they yield more pliable fibres that 

 are more easily felted than the fibres of hardwoods. The 

 wood of poplars, lime-trees, spruce and silver-fir are specially 

 suitable for wood-pulp. Resinous, brittle pinewood is less 

 suitable. Heavy hardwoods are useless for this purpose. 

 Any want of uniformity in the direction of the fibres, or 

 in hardness or colour, reduces the value of the wood. Wet 

 wood yields long fibres ; unsound wood is useless. 



<>f \Vnuil for bt-iiii/ 7V/.S-/W. 



Moderately heavy and moderately hard woods are the best 

 for polishing ; it is more difficult to make a smooth surface 

 on very hard and soft woods. The radial and tangential 

 sections are the easiest to polish. Woods with large medullary 

 rays are polished less easily than those with line rays. Large 

 vessels evenly distributed that absorb much polish imply 

 wood that can be well polished, especially when the wood 

 has a natural lustre. Mahogany, rosewood, satinwood, and 

 the woods of ash, walnut, olive, pear, box, almond, pistachio 

 and maple, polish well ; oak, mulberry and cherry and most 

 other broadleaved woods are less suitable, while conifers (except 

 yew and rootstock of Callitris quadrivalvis *) that have no 

 vessels, can be polished only with difficulty and unsatisfactorily. 



(I. Wood-bleaching 



In wood-bleaching f the tannin, resin, etc. are removed from 

 wood by boiling it in a solution of potash or soda, and it is then 



* Mathey, who states that this X. African wood is very beautiful. 

 f -Mellniaini, " Lehrbuoh <lcs liei/ens, Bleichens, Polizierens u. Lackierens dcr 

 Hol/.cr." I'.erlin. ISM. 



i2 



