The apparatus employed is shown in Figs. 28, 29, and 30. Fig. 28 illustrates an arrangement of grinding apparatus fixed direct on to a turbine. The stone is fastened on to the shaft S worked by the turbine T. The wood in the form of small blocks is kept in contact with the stone by a number of hydraulic presses P. {108}

A somewhat similar arrangement, but placed horizontally, is shown in front and side elevation in Figs. 29 and 30. The same letters correspond.

The ground and sorted pulp is made into thick sheets by means of the board machine shown in Fig. 31. The pulp mixed with water passes down the shoot D into the vat B in which the cylinder K revolves. This cylinder is covered with wire-cloth, and as it revolves it takes with it a certain quantity of pulp in the form of a continuous sheet. This sheet is taken on to the endless travelling felt F by the small couch roll E. When it reaches the rolls C it is wound round the upper one, from which it is removed when a sufficient thickness is obtained. Obtained in this form the pulp is readily transported.

The woods commonly employed are white pine and aspen. The latter yields a pulp of a better colour, but of inferior strength than the former.

Paper containing mechanical wood pulp is very liable to become discoloured by the action of air and light, the ligno-celluloses being much more readily acted upon than the celluloses isolated from them. Such fibre is, moreover, devoid of much felting power; it has, in fact, little to recommend it but its comparative cheapness. It is nevertheless used in large quantities, some cheap papers being made entirely from it. {109}