MANUFACTURES, ETC. 239 



the various chemical reactions which take place 

 during manufacture, a brief outline of the 

 methods employed will suflS.ce for our purpose. 

 Again we repeat that full and lucid details may 

 be found in Messrs. Cross and Sevan's work 

 from which our information is derived. 



There are two leading methods of obtaining 

 wood pulp by chemical means, the alkaline pro- 

 cess and the bisulphite process. In the former 

 process wood of inferior quality may be used, 

 for the action of the chemicals employed is so 

 powerful that rotten wood, knots, etc., are all 

 attacked. In the latter process, on the other 

 hand, carefully selected raw material is essential, 

 containing httle resin and uniform in colour and 

 structure. 



In the alkahne process the bark is stripped 

 from the timber and the wood chipped and 

 passed through a mechanical " duster " to the 

 boiler or digester. The boilers are either of the 

 horizontal cyhndrical or spherical rotary types. 

 Upon the wood is poured a lye, consisting of 

 6 to 8 per cent caustic soda ; the boiler is then 

 closed and heating is rapidly taken to a maxi- 

 mum steam pressure and so maintained for 8 

 to 10 hours. " The resulting pulp is washed by 

 the process of economic Uxiviation in successive 

 tanks, and is obtained of a brownish grey colour. 



