Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/243

PAPER 225 The sheet of paper is formed in the following way. The vatman, fig. 1 2, takes up enough pulp on the mould to fill the deckle. He runs the stuff evenly over the mould from the foreside to the back, throwing back any pulp FIG. 13. Mould. proper number of sheets of paper, with a felt between each, has been placed in the pile called a " post, " it is taken to the press, and a great quantity of the water is pressed out, leaving the sheets of paper sufficiently dry to be handled by the " layer," who places them in packs, one sheet above the other, and after being parted sheet from sheet they are re-pressed. After this the paper is hung in a drying loft on cow-hair ropes in spurs of three to five sheets thick until dry. It is then sized by passing the spurs through a strong solution of gelatin contained in a long trough. The paper passes along on an endless felt, and is freed from superfluous size by press rolls at the end of the trough. It is then parted again to prevent the sheets from sticking together, and is again dried at a temperature of 70 to 80 Fahr. After being picked and then glazed between plates, it is sorted and finished in the same way as other paper, but with much greater care. It will readily be understood that the expense of manu facturing paper in this way is very much greater than by machinery ; but the gain in strength, partly owing to the time allowed to the fibres to knit together, and partly to the free expansion permitted them in drying, still maintains a steady demand for this class of paper, and probably 60 to 70 tons per week are made in Great Britain at present. Fig. 12. which may be superfluous, and then gives the mould the " shake," & gentle shake both along and across the mould, causing the water to run through the wirecloth while the pulp which forms the sheet of paper stays on the top. The vatman then brings the mould to the stay ; it is placed by the coucher on an inclined elbow, where some more water drains away, and he afterwards turns it over on the felt, leaving the sheet of paper on the felt. When the TO In America, papers of great strength are manufactured by machinery, and not much hand-made paper is made. Manufacture from other Substances than Rags. Although the better varieties of both writing and printing paper ar& still manufactured from rags, the supply of these has been found altogether insufficient to supply the increasing demand for paper, and other fibres have to a great extent been substituted for the cheaper classes of paper. First among these is ESPARTO (q.v.). 1 The treatment of esparto does not greatly vary from that of rags. On arrival at the mill the grass is sorted ; that is to say, it is spread out in bunches on a table with a wire gauze cover, and these are shaken to remove the dust, while the roots and weeds are removed by picking. This is technically known as dry picking. In some mills this process is done mechanically by aid of a duster, which removes dust and other heavy impurities from the esparto, but it must then be picked in the wet state after boiling. The boiling is done in the same way as rags, but with a larger proportion of caustic soda. Mr Thomas Routledge, the introducer of esparto, specifies 10 per cent, real caustic soda, but with improved forms of boilers such as Roeckner s or Sinclair s, operating at 40 to 50 lb pressure, a considerable saving on this amount of alkali may be effected. The subsequent treat ment of esparto is similar to that for rags ; it is again " wet-picked " after boiling, then washed and bleached, a much larger quantity of chloride of lime being required than in the case of rags. It can be treated either alone or mixed with rags, and forms a very mellow bulky paper admirably adapted for printing purposes. A considerable quantity of straiv is used both in Britain and in America for paper-making. In general it is mixed either with rags or with esparto, being of too brittle a nature when bleached to make into paper alone. It is generally dusted after arrival at the mill, in many cases cut into chaff before the boiling operation, so as to allow the soda freer access to the fibres, and boiled under high pressure with considerable quantities of caustic soda up to 15 per cent, of real caustic. It is then washed either separately or along with esparto, and bleached in the ordinary way. As at present treated, the yield averaging only 33 to 40 per cent., straw will not come into general use, except in cases where the raw material can be bought on unusually advantageous terms. There is no doubt that, in this case especially, a more rational method of extracting the cellulose than by boiling under high pressure with a large amount of caustic soda is most desirable, for, many of the fibres of the straw being extremely fine, these are to a considerable extent actually dissolved by tlae soda, and, whereas theoretically straw with 15 per cent, moisture ought to produce 45 per cent, cellulose, by the soda treat ment not more than 33 per cent, are obtained, where a good white colour is desired. The only other fibre which has seriously threatened to compete with rags or esparto is wood. From the fact that the supply of this raw material is apparently inexhaustible, a great deal of attention has been paid to methods for reducing it to a fibre capable of being made into paper. These divide themselves into two (1) mechanical and (2) chemical treatment. (1) The wood generally selected for this purpose is white pine or poplar. It is cut into slabs of convenient size, which are then pressed against the face of a mill-stone revolving at a high speed, while a flow of water conveys the fibres of wood away as they are separated. They are then sieved according to fineness, collected, and pressed into pulp or half stuff, which is used for admixture in inferior papers, or even, in some cases, for making paper. By 1 The imports, which in 1863 amounted to 18,000 tons, had risen to 100,000 tons in 1870, and in 1883 reached 206,000 tons. XVIII. :