MANUFACTUEES, ETC. 237 



steaming process is a complex attack of tlie 

 lignone components of the wood with reactions 

 of hydrolysis, oxidation and condensation, the 

 effect on the wood being a loosening of the 

 fibres, and incipient breakdown, as a result of 

 which the action of the stones is attended with 

 less disintegration than in the case of raw wood. 

 At the same time, portions of actual encrusting 

 matters are gelatinized and converted into a 

 "colloidal condition, and this, in association with 

 the greater length of fibre, imparts extraordinary 

 toughness and strength to the boards, etc., made 

 from brown mechanical pulp. The reactions of 

 oxidation and condensation under treatment with 

 steam produce brown colouring matters, which 

 cannot be efiectively removed, so that the 

 application of this pulp is restricted to the 

 manufacture of ' leather boards ' and brown 

 wrapping papers. In a modification of the pro- 

 cess, the wood is alternately boiled with water 

 and steamed under pressure, whereby a pulp of 

 better quality and paler colour is produced. 



" Mechanical pulp whether ' white ' or ' brown' 

 is in many cases worked up into finished boards 

 at the mill. If the pulp is required for shipment 

 or transport it is made up roughly into thick 

 sheets by means of a board machine. . . . 

 Obtained in this form the pulp is readily trans- 

 ported, and comes on the market almost invari- 



