(p. 273) Special Industrial Developments.—From the point of view of the chemist there has been a very large development of the cellulose industries during the last five years. This is not so much marked by the gradual and progressive growth of the well-established industries, as by the success of the newer ones, with the attendant forecast of enormous developments of the industries in artificial products, the manufacture of which rests upon a purely chemical basis. We can, of course, only treat them from this limited standpoint, and so far as they involve and elucidate chemical principles.
I. Chemical Treatments of Raw Materials.
(a) Flax-spinning.—The treatment of the roving on the spinning-frame by the addition of reagents to the macerating liquid—otherwise and usually hot water—continues to be justified by results. The technical basis of the process and the reactions determined in the spinning-trough by the alkaline salts used—chiefly sulphite and phosphate of soda—is set forth in the original work, p. 280. Since that time a sufficient period has elapsed to judge the effects, both technical and industrial, by the results of a commercial undertaking based on the exclusive use of the process. Such a concern is the Irish Flax Spinning Company of Belfast. At this mill the experience is uniform and fully established that by means of the process the drawing, i.e. spinning, quality of inferior flaxes is very considerably appreciated, enabling the spinner to use such flaxes for yarns of fineness which are unattainable by the ordinary method of spinning through hot water. Notwithstanding the success of this undertaking the development of the method is still inconsiderable. It is none the less a further and forcible demonstration of the existence of margins of increased technical effect which it is the work of the scientific technologist to exploit.
(b) Wood-pulp and Methods of Manufacture.—There is a steady growth in the consumption of wood-pulps (cellulose) relatively to other materials. In regard to the paper-trade of the world, this continues to be one of the most prominent characteristics of its evolution. In the United Kingdom the conditions of its competition are of a more special kind by reason of the firm foothold of esparto, which is a most important staple in the manufacture of fine printings. Whereas the consumption of esparto remains nearly stationary at about 200,000 tons per annum, the importation of wood-pulps has shown the extraordinary rate of increase of doubling itself every five years. But in the group 'wood-pulps' the trade returns have until recently included the 'mechanical' or ground wood-pulps. From 1898 we have separate returns for the chemical or cellulose pulps, and in 1899 the tonnage reached nearly to that of esparto, with a total money value about 80 p.ct. greater. When it is remembered that this is one of the newer chemical industries in cellulose products, and that these large commercial results have been accomplished during a period of twenty years, we are impressed with the scope of the industrial outlook to the chemist, afforded by the arts of which cellulose is the foundation.
It may be noted that there have been no important developments in the purely chemical processes involved in the several systems of preparing cellulose from wood. The acid methods (bisulphite processes) have developed much more extensively than the alkaline, the latter including the caustic soda and the mixed sulphide ('Dahl') process. The bisulphite processes depended in the earlier stages upon the efficiency of lead-lined digesters. But the problem of acid-resisting linings has been much more perfectly solved in later years in the various types of cement and other silicate linings now in use. The relative permanency of these linings has had an important effect on the costs of production. Further economies result from the use of digesters of enormous capacity, dealing with as much as 100 tons of wood at one operation. As a combined result of economic production and active competition, the selling prices of 'sulphite pulp' have moved steadily downwards in relation to other half-stuffs and raw materials. As a necessary consequence the prices of those which it has gradually displaced have depreciated, and a study of the price and tonnage-equilibrium as between rags, esparto, and wood-pulp over a series of years forms an interesting object-lesson in the struggle for survival which is an especial mark of modern industry. For these matters the reader is referred to the special literature of the paper-making industry.[12]
It is not a little remarkable that the main by-product of these bisulphite processes—the sulphonated derivatives of the lignone constituents of the wood—is still for the most part an absolute waste, notwithstanding the many investigations of technologists and attempts to convert it to industrial use (see p. 149). Seeing that it represents a percentage on the wood pulped equal to that of the cellulose obtained, it is a waste of potentially valuable material which can only be termed colossal. Moreover, as a waste to be discharged into water-courses, it becomes a source of burden and expense to the manufacturer, and with the increasing restrictions on the pollution of rivers it is in many localities a difficulty to be reckoned with only by the cessation of the industry. The problem in such cases becomes that of dealing with it destructively, i.e. by evaporation and burning. In this treatment the obviously high calorific value of the dissolved organic matter (lignone) appears on the 'credit' side. But where calcium and magnesium bisulphites are used, the residue from calcination is practically without value. It appears, however, that by substituting soda as the base the alkali is recoverable in such a form as to be directly available for the alkaline-sulphide or 'Dahl' process. As a more complicated alternative the soda admits of being recovered on the lines of the old black-ash or Leblanc process, and the sulphur by the now well-established 'Chance' process, for which, of course, an addition of lime is necessary to the fully evaporated liquors previously to calcining. The engineering features of the system, so far as regards evaporating and calcining, are the same. For economic working there is required (a) evaporation by multiple effect and (b) calcining on the continuous rotary principle. For the latter a special modification has been devised so that the draught of air is concurrent with the movement of the charge in the furnace, securing a progressively increasing temperature within the furnace. This interesting development of the chemical engineering of wood-pulp systems has been elaborated by two well-known technologists, Drewson and Dorenfeldt, and readers who wish to inform themselves in detail of these developments are referred to the various publications of these inventors.
Assuming the present necessity of a destructive treatment of the by-products of the bisulphite processes, the scheme has many advantages. The soda-bisulphite liquors are more economically prepared; the pulp obtained is superior in paper-making quality to that resulting from the lime or magnesia (bisulphite) processes: it is more economically bleached.
Then, as pointed out, the soda may on the one plan be obtained in a form in which it is immediately available as a powerful hydrolysing alkali in the manufacture of a 'soda' pulp. These two systems become, therefore, in a new sense complementary to one another. Lastly, it is obvious that the employment of soda as the base opens out a new vista for developing the electrolytic processes of decomposing common salt.
The authors have assisted in preparing plans for a comprehensive industrial scheme combining all these more modern developments. In this scheme it is only the combination which is novel, and as it involves no new principles in the chemical treatments of the materials we are not further concerned with it than to have briefly sketched its economic basis. This may be summed up in result in the important question of cost and selling price, and the estimate is well grounded that by means of this scheme bleached wood-pulp can be sold on the English market at 10l. a ton. It is important to note this figure and to compare it with the prices of twenty years ago. The fall has been continuous, notwithstanding the influence of the opposing factors of increasing consumption, exhaustion of accessible supply of timber, and relative appreciation of the essential costs of steam, chemicals, and labour. It is important in forecasting the future, since the youngest and apparently most promising of the 'artificial' cellulose industries employs wood-cellulose by preference as its raw material (see p. 173).
As a last point it must be considered that as chemists we are bound to anticipate the realisation of value in the soluble by-products of the bisulphite processes. Outside the intrinsic interest attaching to the solution of this problem, it carries with it the promise of a further economy in the production of wood-cellulose.