WOOD PULP. 67 



a special contrivance, and ground down again to the necessary- 

 fineness. When the reduction is complete, the superfluous water 

 is removed, and the pulp is sorted out into different qualities ac- 

 cording to its fineness. In Germany alone over 6,000,000 cubic 

 feet of wood is made into pulp by this method. The pulp thus 

 obtained is used principally as paper stock. 



II. The Chemical process. — The wood is divided into billets 

 and barked. The billets are then sliced obliquely by a special 

 cutting machine into pieces about ^-inch thick. These pieces are 

 passed between fluted rollers, which break them up into chips 

 about ^-inch long and from ^ to ^-inch thick. The chips are next 

 put into pierced iron barrels placed inside a large boiler. The 

 boiler is then hermetically closed and completely filled with a 

 strong lye of caustic soda, and fires are lighted below. After 

 from three to four hours, during which the pressure of the steam 

 inside reaches a maximum of about 10 atmospheres, the process of 

 digestion is complete, the fires are put out, and the boiler is 

 emptied and opened. The contents of the barrels, which is now 

 pure cellulose (the maceration having dissolved away all the coat- 

 ing and cementing substances), are thoroughly washed with plenty 

 of water, refined and bleached, and passed bet-ween several sets of 

 rollers, from the last of -which the entire mass issues forth in ap- 

 pearance resembling a large sheet of felt. The sheets, while still 

 moist, are sprinkled over with sand and rolled up and formed into 

 bales. 



From the lye after it leaves the boiler, and from the first wash- 

 ings, from 75 to 80 per cent, of the soda is recovered and can be 

 used over again. The substance obtained by this process is the 

 pure cellulose of the wood in an unbroken condition, and is, there- 

 fore, not only adapted for paper stock, but also for the manufacture 

 of pressed articles, for stuffing cushions, for packing, for filtering, 

 &c. The yield of cellulose by this process is roughly 25 per cent. 

 of the air-dried weight of the wood. 



Mb. Eoutledge's method of preparing bamboo fibre for 

 PAPER stock. — According to this gentleman the J'oung bamboo 

 culms, while they are still semi-herbaceous, should he passed be- 

 tween two rollers resembling the rollers of an ordinary iron sugar- 

 cane mill. This crushing presses out all the sap and glutinous 

 substances, and reduces the culms to the condition of long flexible 

 ribbons, which, after being dried, can be made up into easily ex- 

 portable bales. The cleaning and bleaching processes can be efFected 

 at the regular paper mills as in the case of rags and raw fibres. 



Wood suitable fob paper stock. — Dark-coloured woods are 



