Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/244

226 this means of treatment, however, the wood is not split up into its ultimate fibres, but is left with all the incrust- ing matter attached, and the pulp and paper so obtained are only fitted for the commonest purposes. (2) Many efforts have been made with the view of preparing wood chemically, so that the resulting fibre might be introduced into fine papers, and latterly with considerable success. In the earlier processes, patented by Houghton and Sinclair, wood was boiled with about 20 per cent, real caustic soda under a pressure of from 10 to 14 atmospheres. By this means, with certain improvements in detail, dictated by experience, so-called chemical wood pulp is prepared in large quantities on the Continent, and is imported as pulp into England to a considerable extent. In America this process has been extensively adopted. While pulp of very fair quality is prepared in this way suitable for papers where a perfectly white colour is not required, there is no room for doubt that the action of the caustic soda solution at the extreme temperature which a pressure of upwards of 10 atmospheres involves, leads to a certain extent to a degradation and consequent weakening and browning of the fibres, and a great deal of work has been directed to the surmounting of this difficulty. The result has been a series of patents, all containing the same principle, namely, the treating the wood with a chemical agent which should prevent oxidation and subsequent degradation of the fibres from taking place. Such patents are those of Mitscherlich and Francke (bisulphite of lime), Ekman and Graham (bisulphite of magnesia). While these all contain a common principle, they differ in detail, as to pressure, blowing off of the sulphurous acid gas, <tc., but they all present a very marked resemblance to Tilghmann s expired patent, 1866, No. 2924. The pulp produced by all those processes is of excellent quality; and, according to the statements of the patentees, it can be prepared at a cost greatly lower than by the soda process. The strength of the fibre is maintained unimpaired even after bleaching, and white paper made solely from such pulp is in every respect superior to that manufactured solely from pulp prepared by boiling with caustic soda. Dr Mitscherlich s process has been extensively adopted in Germany, and there seems little doubt that these pro cesses will in time supplant the use of soda in the case of wood. The great objection to them all is that, as they all depend on the use of bisulphite, which, being an acid salt, cannot be worked in an iron boiler, the boiler must l>e lined with lead ; and great difficulty has been encoun tered in keeping the lead lining of the boiler in repair. This is a difficulty, however, which will probably be over come with further experience. The objection to cellulose prepared from wood by all the acid processes is that it is not pure, but a considerable quantity of incrusting matter is left in the fibre, and hence the paper manufactured from it solely is harsh in character and very transparent; to pro cure a pure cellulose, it must be exhausted in an alkaline solution subsequent to the treatment with acid. The waste of jute is largely used in the manufacture of coloured papers, but it has not hitherto been found possible to thoroughly bleach this fibre without at the same time destroying its strength. A long series of experiments, with a view to the intro duction of bamboo fibre for paper making, has been undertaken by Mr Thomas Routledge, the well-known introducer of esparto, who recommends the employment of the young shoots. It may well be doubted whether the bamboo has any chance as a competitor against the new processes for preparing wood. A host of other fibres have been tried from time to time, such as dis grass from the north coast of Africa, the leaves of the dwarf palm, sugar-cane refuse, the stalks of the hop plant, nettles, peat, Phormium tenax from New Zealand, with many others (see Dr Hugo Miiller s Pflanzenfaser}, but none with such success as to call for notice here. Soda Recovery. In the preparation of esparto, wood, and other raw material for manufacture into FIG. 14. Porion Evaporator. paper, large quantities of caustic soda are employed, and, as the resulting liquid after boiling the fibre in caustic soda solution is strongly alkaline and dark-coloured, it is very desirable to keep it out of the rivers. In order to effect this it is in many mills evapo rated, and the soda it contains recovered, and, after caustici/ing, re-used. Many forms of evaporator have been proposed, and of late years great improvement has been made in their construction. Pro bably the best form is the Porion evaporator (fig. 14). This consists of an evaporating chamber A, on the floor of which a few inches of the liquid to be evaporated rest. By the action of fanners B, B re volving at a high speed and dipping into the liquid, it is thrown up in a fine spray through which the heated gases pass to the chimney. After being concentrated in the evaporating chamber the liquid ilows into the incinerating furnaces C,C, where the remaining water is driven off by the heat of the fire D, and the mass afterwards ignited to drive off the carbonaceous matter. A considerable feature in this evaporator is Menzies and Davis s patent smell chamber E, a cham ber filled with masonry in which the strongly-smelling gases from the incinerating furnace are allowed to remain at a red heat for a short time. After being recovered, the soda, in the form of crude car bonate, is lixiviated and re-causticized by boiling with milk of lime. Sizes of Paper. The following are the ordinary sizes : Writing Papers. Book and Drawing Papers. Printing Papers. Cartridge Papers. Ins. Pott . . " 124 x 15 Ins. Foolscap 14 x 18f Ins. Crown 16}x21 Ins. Foolscap 14 xlSf Double pott 15 x 25 Demy 15| x 20 Demy 17fx22.$ Demy 17f x 22J Foolscap 13} x 16 Medium 17^x22^ Medium 18} x 23 Royal 19 x 24 Double foolscap 16| x 26i Royal 19 x 24 Royal 20 x 25 Super royal 19} x 27 Foolscap and third 131 x 22 Super royal 21 x 27 Imperial 21 x 26 Foolscap and half 13} x 24| Imperial 22 x 30} Double pott 15 x 25 Elephant 23 x 28 Pinched post 14^x18^ Elephant. .. 23 x 28 Double foolscap 17 x 27 Post .. 15^x19 Double elephant . 26J x 40 Double crown 20 x 30 Double post 19 x 30J Atlas. 26} x 34 Double demy 22 x 35 J Lare post 16x20f Columbier 23x244 Double large post 20f x 33 Antiquarian. 31 x 53 Copy 16| x2 Medium 18 x 22