Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/240

222 recovered. Between the first and second suction box the dandy roll, a skeleton roll covered with wirecloth, revolves on the top of the pulp. By means of raised wires on it in the form desired the paper is rendered thinner at these parts and a water-mark is produced. In order to secure regularity in the layer of pulp, as also to increase the strength of the paper, a lateral motion is communicated to the wire by the shake O. The half-dried pulp now passes between the couch rolls, where it receives the first pressure. The under couch roll generally consists of a brass shell fixed by iron rings to a spindle ; the top roll may be either similar to the lower one or made of mahogany, and is always covered with a felt jacket. Pres sure is applied to the ends of the top roll by means of levers and weights. From these the sheet of partially dried pulp is carried by endless felts through the first and second press rolls R and S. The press rolls are either made of solid iron, or may with advantage have a brass shell shrunk on. Having been freed by these from a great part of its water, the web of paper is carried over the steam-heated cylinders T, T. The first two cylinders are generally bare, and the heat applied to these is gentle ; in the case of the others, the paper is kept close to the cylinder by means of endless felts. The web then passes through the intermediate rolls U in a half-dried state, over three more cylinders and the calenders Y. These are heavy iron rollers heated by steam internally and polished externally. Their object is to communicate a gloss to the web of paper. It is then wound up on the reel W, and these reels when filled with paper are removed as required FIG. 5. Paper Machine Horizontal Section. to the paper cutter. In cases where the paper is to be sized with gelatin after leaving the machine, it is wound up rough. A modification of the Fourdrinier machine, suitable for the manufacture of .thin papers and those which only require to be smooth on one side, is shown in fig. 6. It consists of an ordinary paper machine as far as the couch rolls A, A. From these the paper is carried backwards on the top of the endless felt B till it comes in contact with the large steam-heated cylinder C at d. Here it adheres to the cylinder, being pressed against it at the same time by the press roll E. The paper then continues round the surface of the cylinder, and is wound up dry on reels at G. The felt washer H is a box filled with water through which the felt passes as it travels. After this the paper is cut or glazed in the usual way. At this stage papers which require to be hard-sized, principally the better sorts of w-riting papers, are sized with gelatin or " tub-sized. " This is done occasionally by passing the sheets separately through a trough contain ing a strong solution of gelatin, and afterwards hanging them up to dry in the same way as hand-made papers, but in general the paper is sized and dried in the web after leaving the paper machine. For this purpose a sizing and drying machine is used (fig. 7). The web of paper to be sized is shown at A. From this it is passed through a trough B containing a strong solution of gelatin into which a certain amount of alum is introduced ; after passing through this by means of the size rolls C, C, it is passed through the press rolls D, which squeeze out the super fluous size from it, and rewound on a reel at E to allow