Sulphite Fibre and Resin.—A German manufacturer sent the following communication to the Papier Zeitung, which may be interesting to the users of sulphite pulp:—"In making [disintegrating] cellulose by the soda or sulphite process, the object in boiling is to loosen the incrusting particles in the wood, resin included, and to liberate the fibres. The resin is dissolved both in the soda and sulphite processes, but in the former it is at the same time saponified, and is consequently very easily washed out. In the case of sulphite fibre, however, the resin attaches itself by its own adhesiveness to the fibres, but can also be removed by as hot washing as possible, and adding a little hydrochloric acid, which produces a very great effect. At the same time, however, sulphite fibre loses in whiteness by thorough washing, and assumes a reddish-grey shade. As the paper manufacturer insists upon white fibre, the manufacturer of sulphite fibre not only often omits washing, but adds some sulphite solution (bisulphite of lime). This not only enables him to give his customers white fibre, but he also sells a quantity of the incrusting particles and sulphite residuum as cellulose.
"So long as the manufacturer looks more to white than to well-washed cellulose, or does not wash it well before working up the fibre, these annoyances cannot be avoided. Not only this, but other disadvantages will be added in the course of time, as the action of the sulphurous acid in the pulp will have very injurious consequences on metals—[and on the fibre itself?] especially iron—coming in contact with it. This should be the more avoided, as the whiteness of the unwashed cellulose is of very short duration. The paper made from it soon turns yellow and becomes brittle. Well-washed sulphite fibre, on the other hand—provided no mistakes have been made in the boiling process—makes a strong, grippy paper, which can withstand both air and sunlight. I have made no special studies as to resin, but believe that pine and fir act differently, especially with solvents."
Adamson's Process.—Mr. W. Adamson, of Philadelphia, obtained a patent in 1871 for the use of hydrocarbons in the treatment of wood. His process consisted in treating the wood with benzine in closed vessels, under a pressure of 5 to 10 lbs., according to the nature of the wood. His digester consisted of an upright cylinder, in which the wood-shavings were placed between two perforated diaphragms. The mass was heated beneath the lower diaphragm by a coil through which steam was passed. The vapours which were given off were allowed to escape through a pipe on the top of the digester, to which was connected a coil immersed in a vessel of cold water, and the condensed liquid then returned to the lower part of the digester. The remaining portion of the benzine in the digester, which was still liquid but saturated with the extracted matters, was drawn off through a faucet at the bottom. Benzine being a very cheap article in America, a similar process was recommended in another patent by the same author for extraction of pitch and tar from rags [tarpaulin, ropes, &c.?], and for removing oil from rags and cotton waste.
Sulphide Processes.—Many attempts were made about thirty years ago, and in subsequent years, to employ the soluble sulphides as a substitute for caustic soda in boiling wood and other fibres, but these processes do not appear to have been very successful. Later improvements in the construction of boilers or digesters, however, seem to have induced further experiments in this direction, and we understand that several sulphide processes are being worked on the Continent, the processes of MM. Dahl and Blitz being amongst them. One of the supposed advantages of these sulphides over caustic soda is that by evaporation and calcination of the liquors, or leys, by which the organic matters become destroyed, the original product would be recovered, which merely requires to be dissolved out for further use. There are, however, several important objections to the use of sulphides in this way, amongst which may be mentioned the deleterious vapours which they emit; and this alone would doubtless prevent their employment—at all events in this country.
II. Mechanical Processes.—Besides the various chemical methods of separating cellulose from woody fibres, before described, certain processes have been devised for reducing wood to the condition of pulp directly by mechanical means without the aid of any chemical substance whatsoever. In this direction Heinrich Voelter, of Wurtemburg, appears to have been the first to introduce a really practical process for the conversion of wood into pulp for paper-making, although, as far back as 1756, Dr. Schaeffer, of Bavaria, proposed to make paper from sawdust and shavings mechanically formed into pulp: the process was not successful, however, with the machinery then at his command.
Voelter's Process for Preparing Mechanical Wood Pulp.—In 1860-65 and 1873 Voelter obtained patents in this country for his methods of treating wood mechanically, and the process may be thus briefly described:—Blocks of wood, after the knots have been cut out by suitable tools, are pressed against a revolving grindstone, which reduces the material to a more or less fine condition, but not in a powdery form, and the disintegrated fibre is caused to press against a wire screen, which allows the finer particles to pass through, retaining the coarser particles for further treatment.
Fig. 17A.—Voelter's Wood-pulping Machine.
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The apparatus employed, which is shown in Fig. 17A, consists of a pulping apparatus A, with vat K, in which the revolving stone S is placed; the blocks of wood are held against the stone at p p, and water is introduced at G, and the revolving stone carries the pulp against the screen E, which admits the passage of the finer particles of the wood, while the coarser particles are led by the trough F to the first refining cylinder B, after passing through an oscillating basket, which retains the coarser particles. From thence it is led through a distributing apparatus and hopper C, to be uniformly supplied to the refining cylinder D, these cylinders being of the ordinary construction, and, as usual, covered with fine gauze wire sieves. The ground material which fails to pass through the sieves is transferred by an elevator to the millstones E, which are of ordinary construction, and after leaving these unites with the finer fibres which pass through E, the whole now entering a mixing reservoir F, whence it is thrown on to the cylinder G, and the pulp which passes into this is distributed on to a similar cylinder H, the contents of which then passes through the last cylinder I, which is differently constructed to the others, inasmuch as its lower part is surrounded by an impervious leather jacket, so that the pulp ascends in order to enter it. The disintegrated fibres that are retained by the wires of the cylinders pass into the refiners, which consist of a pair of horizontal cylinders of sandstone, one of which (the upper one) only revolves, and by the action of these the coarser fibres become further reduced, the finer particles, as before, passing through the wire gauze of the cylinders, the operation being repeated in the same order until the whole of the fibres have passed through the sieves.