or injected into the boiler. There is thus forming in the closed boiler a solution containing an excess of sulphurous acid above that required to form, in combination with the base, a monosulphite. The operation of injecting sulphurous acids, or the sulphites, may be repeated from time to time during the boiling, so as to fully maintain, and if necessary increase, the strength and efficiency of the chemical solution. It is said that by this process a saving of the chemicals employed is effected, as little or no sulphurous acid gas is lost during the time the gaseous hydrocarbons, air, and other gaseous matters are being expelled from the fibrous materials. If an open vessel is used instead of a closed boiler, it will be necessary to keep the solution at a fairly uniform strength, and if necessary to increase the strength, but the result will be substantially the same; but as it is evident that, when using an open boiler, the excess of sulphurous acid supplied during the boiling will be constantly driven off as gas, it must be replaced by further injections, while the acid fumes may be conveyed away and condensed, so as to be available for further use. When the fibrous substances are boiled as above, with the addition of potash, soda, etc., during the boiling, the result will be equally beneficial. The inventor prefers to inject the sulphurous acid or its combinations into the boiler at the bottom, and to cause it to come in contact with the solution therein before reaching the fibrous materials. For this purpose there is formed a kind of chamber beneath the boiler, but separated from it by a perforated disc or diaphragm of lead or other suitable material not acted upon by the solution, so as to allow the latter to fill the chamber, to which is connected a pipe, through which the sulphurous acid or solutions of the sulphites is forced by any suitable apparatus.
Objections to the Acid or Bisulphite Processes.—While the various methods of boiling wood in caustic soda at high temperatures are well known to be open to serious objections, the acid treatment of wood also presents many disadvantages, which it is to be hoped may be yet overcome. In reference to this, Davis makes the following observations:—"In the acid treatment of wood for the purpose of converting the fibres into pulp for use in paper manufacture, the general practice has been to use alkaline solutions of soda, combined in various proportions with certain acids, such, for instance, as sulphurous acid, hydrochloric acid, etc. These solutions have been heated in digesting vessels, and the high temperature resulting from this process of heating developing a pressure of from six to seven atmospheres, the wood being disintegrated by the action of the boiling solutions, the gum, resinous constituents, and other incrustating or cementing substances that bind the fibres together are decomposed, destroyed, or dissolved, while pure cellulose, which constitutes the essential element of the ligneous fibres, is separated therefrom. To this end high temperatures had to be employed, otherwise the disintegration was found to be only partial, the wood remaining in a condition unfit for further treatment. The high temperature not unfrequently converts a large proportion of the resinous and gummy constituents of the wood into tar and pitch—that is to say, carbonaceous bodies that penetrate into the fibre and render its bleaching difficult, laborious, and costly, while the frequent washing and lixiviation necessary to bleach such products seriously affect the strength of the fibre and its whiteness, and also materially reduce the percentage of the product, in some instances to the extent of 18 per cent. These difficulties and detrimental results materially enhance the cost of production, while the fibre itself suffers considerably in strength from the repeated action of the chloride of lime. … The difficulties are chiefly due to the carbonisation of certain constituent parts of the fibres under temperatures exceeding 212° F., such carbonised matters being insoluble and incapable of being bleached, and as they permeate the fibre, cannot be entirely removed.
"To overcome these difficulties, the wood should be chemically treated at a temperature sufficiently low to ensure that the decomposition of the connecting substances of the fibres will remain chemically combined with the other elements, such as hydrogen, oxygen, and nitrogen, in order to obtain an increased product of superior quality and render the process more economical."
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
