234 TIMBEES AND THEIR USES 



of th.e stone, and serve to carry ofi the pulp 

 to the sides of the stone, in addition to giving 

 increased grinding surface. The presence of the 

 blocks of wood against the stones is steadily 

 maintained by screws worked by suitable gear- 

 ing ; this is necessary in order to obtain a pulp 

 of* uniform character. A stream of water is 

 kept constantly playing on the stone; by this 

 means the pulp, as fast as it is formed, can be 

 conveniently carried away. It is first pressed 

 through a rake, which . retains small pieces of 

 wood that have escaped grinding. The stream 

 of pulp then passes through the sorters, the 

 object of which is to keep back such portions 

 of the wood that have not been sufficiently dis- 

 integrated. These consist of cylinders about 

 three feet long and two feet in diameter, covered 

 with a coarse wire-cloth. The fibres that are 

 retained by this wire, fall into the refiners, which 

 consist of a couple of horizontal cylinders of 

 sandstone, the upper one only of which revolves. 

 Here they are further disintegrated, and are again 

 passed through the wire-cloth ; this is repeated 

 until all the fibres have passed through. The 

 pulp, after passing through the first sorter, may 

 be conducted through a series of gradually 

 increasing fineness, and, by this means, be 

 separated into different quaUties. Though pulp 

 so prepared cannot compare with chemically 



