MANUFACTURES, ETC. 235 



prepared stuff, as the fibres are extremely short 

 and have comparatively little felting-power, it 

 may be used with advantage as a sort of filling 

 material. 



" In some grinding machines the stones are 

 mounted horizontally on vertical shafts, but in 

 modern installations the preference appears to 

 be given to the vertical type of stone, mounted 

 on a horizontal shaft. Wood grinders are con- 

 structed for both steam and water power in 

 units often exceeding 1,000 h.p., but in the vast 

 majority of cases the site of the mill is selected 

 where water power is plentiful and the grinders 

 are driven directly from the turbines. 



" Two kinds of mechanical wood pulp can be 

 prepared, according as the wood is found across 

 the grain or in the direction of the grain. The 

 cross-grain fibres are shorter and more mutilated 

 than the long-grain fibres, but the latter do not 

 give so fine a pulp, and the process of long-grain 

 grinding is very seldom used. 



" The quality of mechanical pulp varies within 

 very wide limits according to the texture of the 

 wood (age and seasoning), and the texture and 

 sharpness of the grinding ridges of the stone. 

 The quality of pulp suitable for making heavy 

 boards is quite different from that suitable for 

 printing papers. The effect of variable con- 

 ditions of grinding or the quahty and produc- 



