162 INDUSTRIAL USES OF WuOD. 



makes a better felt. The difference between these two products 

 depends on their mode of manufacture, which will now be briefly 

 described : — 



(a) Mechanical Manufacture of Wood-Pulp. — The wood is 

 barked, cut into pieces ;il)0Ut a foot l()n^^ s])lit, and freed by the 

 chisel and augur from all knots and unsound defects. It is then 

 ground into a pulp by a rotating stone, and subjected to a continual 

 flow of water : the pulp is separated by a special contrivance from 

 the coarser wood-splinters, and ground into a finer state of sub- 

 division, freed from all superfluous water, and pressed under 

 heated rollers into sheets of felt, in which state it is sold to the 

 paper-manufacturers. Material thus produced is termed white 

 wood-pulp. If before being ground, the wood is steamed 

 under a pressure of two to six atmospheres, or merely steeped 

 in boiling water, it yields brown wood-pulp, which is said 

 to have longer fibres and to form better felt than the former. 

 Wood-pulping machines were first constructed by Yolter, in 

 Heidenheim, and have since been greatly improved ; they require 

 a large supply of water both as motive power and for manu- 

 facturing purposes. 



In Germany, in the year 1892, the number of wood-pul]) 

 factories had risen to nearly 600, and consumed annually about 

 1,000,000 stacked cubic meters (35,000,000 stacked cubic feet, 

 or 700,000 loads) of wood, and produced '200,000,000 kilos 

 (200,000 tons) of wood-pulp. In Austria-Hungary, in 1890, 

 there were in active work 200 wood-pulp factories. 



(b) Manufacture of Cellulose. — This manufacture is of two 

 kinds, depending on the use of caustic soda or calcium-sulphite 

 to macerate the wood. The present tendency is greatly in 

 favour of the latter process. 



Where soda is used, the wood, freed from bark, knots and 

 defects, is cut by a machine into splinters about 2 centimeters 

 thick, which are passed between grooved rollers working like 

 a coffee-mill, and reduced into fragments 2 centimeters long 

 and 5 to 8 millimeters thick. These fragments are then packed 

 in perforated sheet-iron vessels, which are placed in a long 

 horizontal steam-boiler. When the boiler has been filled with 

 the vessels, its cover is fastened down air-tight, it is pumped full 

 of a solution of soda, and boiled over a furnace. After three or 

 four hours, the boiling, which is conducted with a pressure of 



