WOOD-PULP. 163 



about ten atmospheres, should be stopped, and the boiler 

 emptied. The rough cellulose is then washed, sifted, bleached, 

 and rolled by several hot-water drj'ing-rollers, from which it is 

 finally wound off in the form of sheets of felt, which are then 

 sold. The residual liquid yields 75 to 80 per cent, of the soda, 

 which may be used again. 



When calcium-sulphite is used, the wood similarly prepared, 

 as in the soda process, is placed in large boilers containing 

 a solution of sulphite of lime, and boiled for fifty or sixty hours 

 under a pressure of two and a-half to five atmospheres. The 

 calcium-sulphite is prepared in tall towers filled with limestone, 

 through which passes sulphurous acid, produced by roasting iron 

 pyrites, and this passes through raised cisterns of water. The 

 solution of calcium- sulphite thus formed is collected below in 

 reservoirs. The wood-pulp which comes out of the boilers con- 

 sists of soft, crumbling, reddish-yellow pieces, which are pounded, 

 washed and mixed with water, passed through sieves, and pressed 

 by heated rollers into felt, in which condition it is usually sold. 



In Kellner's electrical process for preparing cellulose, wood 

 is boiled in solutions, chiefly of common salt, and during the 

 boiling is subjected to electrical discharges which effect the 

 separation of the fibres. The economic value of this method 

 has not yet been ascertained. 



There are now about seventy cellulose-factories in Germany, 

 which use annually about 700,000 stacked cubic meters (say, 

 500,000 loads) of wood, and produce 80,000,000 kilos (80,000 

 tons) of cellulose. A cubic meter of cellulose yields 4 cwt. of 

 paper. In Austria-Hungary, in 1890, there were about thirty 

 cellulose factories in full work. [Bamboos make excellent wood- 

 pulp.— Tr.] 



Of all the different preparations of wood-pulp, the cellulose 

 prepared by the calcium-sulphite method is preferred, and is 

 much cheaper than the soda method. The mechanical method 

 is, however, cheaper than either. In all these industries, and 

 especially in the mechanical method, the)'e is now-a-days an 

 excess of production over demand. 



2. For utlitr jnirposes. 

 Wood-pulp is used for many other purposes besides paper- 

 making, sometimes usefully, at other times with doubtful 



M 2 



