320 THE UTILISATION OF WOODLAND PRODUCE. 



not bleached (hence the superiority of the white woods above 

 noted). The best size of wood for pulping or for cellulose 

 consists of poles of from 4 in. to 6 in. top-diameter and 6 in. 

 to 8 in. bottom diameter, cut into lengths of about 6J ft. 

 These sections have to be first cleaned and barked, then freed 

 from knots and unsound parts, and cut into convenient lengths 

 before being ground into pulp or chipped for cellulose-making. 



In grinding the wood mechanically for pulp, the billets are 

 pressed lengthways against a hard fine-grained sandstone 

 grinding-stone, rotating quickly with a continuous stream of 

 water dropping between the wood and the stone, to make the 

 woody fibres separate more easily ; and the fibres are then 

 strained, dried, and pressed. The grinding-stones are from 

 3J ft. to 5 ft. in diameter and about 18 in. to 20 in. thick. 

 The pulp-wood is put, 5 or 6 billets at a time, into a box and 

 pressed steadily against the grindstone, and the pulped fibres 

 are carried off on to sieves for straining, these sieves being set 

 at a slight angle and shaken from side to side by means of a 

 crank, there being usually two or three sets of such strainers 

 set one above the other with different-sized meshes. The fine 

 fibres are then pumped up into a churn, reduced there still 

 further by friction, then again passed through strainers, and 

 led off to rollers or to a pressing-machine to get rid of the water 

 and to dry the pulp. Wood-pulp made thus is dull in colour, 

 unbleachable, and the short thick fibres can only be used for 

 coarse paper, pasteboard, or cardboard. It is known as white 

 pulp, but if the wood be steamed under pressure of about 60 

 Ibs. per square in. before being ground, the pulping is easier 

 and the pulp-fibres longer, softer, and more flexible and felty, 

 but darker in colour (brown pulp). The making of wood- 

 pulp is now confined to places having good water-power, but 

 far distant from a cellulose -mill, or where there is not a 

 sufficiently large and constant supply of wood to keep a 

 cellulose-mill always at work. 



