"refining engine," a machine of American origin; the names associated with the invention of these engines are those of Kingsland, Jordan and Eustice, Gould and Marshall. The type which is used very extensively in this country is the Marshall pulp refiner of Messrs. Bentley and Jackson, Limited (Fig. 19 and 20), which consists of two cones, a larger stationary A', and a smaller revolving one A, both provided with beater knives. The smaller is placed inside the larger cone and thus the pulp, during its passage between the

two, is acted upon by the knives. Before leaving this engine, the fibres have to pass between the knives fixed on a revolving disc, B, and the knives, B', on the inside of the chamber in which this disc is enclosed.

Considerable experience is required to judge whether a pulp has been sufficiently beaten. It is the practice to take a small quantity of the pulp out of the beater and to reduce it with water in a small hand bowl; by this means the degree of disintegration of the fibres may be readily ascertained.

In the production of high-class papers and in the dyeing of delicate shades it is of the greatest importance to employ water of great purity, especially in the beating.

size and colouring matters. It is therefore obvious that the quantity added should never exceed the amount required for the decomposition of the bleach present. Hypochlorite in the pulp may be readily detected by means of potassium-iodide-starch paper, which developes a characteristic blue colouration with free chlorine.

SIZING.

The sizing of the pulp is the next of the operations conducted in the beater, which calls for consideration. Paper made from fibres in a pure state, as produced in the beating engine, will not resist water or ink; the pores and the canals in the fibres on the

ANTICHLOR.

Although the removal of bleach and of other impurities formed during the bleaching operation is most completely effected by subsequent washing, it is, in many instances not found possible to carry the washing far enough. Recourse has therefore to be made to decomposition by means of the so-called "antichlors"; the chemical agents mostly in use for this purpose are sodium thiosulphate and sodium sulphite.

With calcium hypochlorite, the first of these salts forms sodium sulphate and calcium chloride, whilst the second one gives calcium sulphate, sodium sulphate, and sodium chloride. On account of the injurious action of the free hydrochloric acid which is formed by double decomposition when thiosulphate is used as antichlor, sodium sulphite has found by far the widest application. Though an excess of antichlor is frequently considered harmless, it may exert an injurious action on

one hand, and the interstices between the fibres in the sheet of paper, on the other hand, absorb liquids very rapidly by capillary attraction. The object of sizing is to fill up the pores and the interstices and thus to make the paper, to a certain extent, ink and water resisting. Wiesner has ascertained that starch was used for the sizing of papers, in very early times, whilst, at a later period glue was employed for surface sizing.

In engine sizing-so called because it is conducted in the beating engine-finely divided rosin is precipitated in the paper pulp. Illig, who invented this method of sizing at the beginning of the last century, recognised that its efficacy is due to the precipitation of free rosin in a state of very minute division; Wurster, Conradin, and Lunge have shown that Illig's view was quite correct.

The "rosin size," or "rosin soap," as it is termed, is prepared by dissolving rosin in soda in a double-jacketed pan which is heated by

starch, especially in the manufacture of high class papers and of papers which have to be heavily loaded. The size should be diluted with water before being added to the beater; after the addition, sufficient time is allowed for it to mix completely with the pulp and the size is decomposed by means of alum or aluminium sulphate. Free rosin is precipitated and basic aluminium sulphate remains in solution; rosin is also precipitated if sulphuric acid is used instead of alum, as has been done by Conradin and others for sizing papers.

The amount of alum or aluminium sulphate added is invariably in excess of the equivalent required for the decomposition of the quantity | of rosin soap used.

Various agents have been proposed as substitutes for rosin size. Of these "viscose (cellulose sulpho-carbonates) calls for special attention. The preparation of this cellulose compound, which is soluble in water, has been described in the first lecture. The necessary quantity of viscose is added to the pulp and allowed to become thoroughly mixed; the decomposing salt, either magnesium sulphate or zinc sulphate, is then added, and gelatinous cellulose is precipitated which acts as a strong sizing agent. In most instances it is found necessary to add a small quantity of rosin size. Papers which have been sized with viscose show a remarkable increase in tensile strength, but the slight discoloration, due to decomposition products of viscose, has up to the present time prevented its being used for the sizing of white papers.

Casein, prepared from milk, is another sizing agent which may be added in solution to the pulp, and which is readily precipitated by alum. Casein, although excellently suited for paper sizing, is but little used on account of its cost. Other sizing agents, such as silicate of soda, aluminate of soda, ammonium albumen, wax, paraffin, &c., are very rarely used.

LOADING.

Mineral substances are often added to the paper pulp whilst in the beating engine; this operation is known as "loading" or "filling." One of the objects of the addition of loading materials is the cheapening of production by the substitution of fibres by a cheaper mineral substance; in many instances, however, the addition of loading materials is, for other reasons indispensable. Certain mineral colours used in paper dyeing act at the same time also as loading materials; to produce uniformity of shade in the dyeing of pulp which

consists of a mixture of different fibres, the introduction of a suitable loading material may be found necessary. Loading also helps to make a paper less transparent, and the smoother surface produced in finishing is better adapted to the requirements of printing. In choosing a loading material two points have to be borne in mind, namely, the properties of the paper for which it is to be used, and the cost of the material itself. The latter point will, to a very large extent, depend upon how much of the material in question is actually carried by the pulp.

China clay (kaolin), which consists essentially of aluminium silicate, is the most commonly used loading material.

Pearl hardening (sulphate of lime), imparts a very superior finish to papers and is therefore employed in the manufacture of highclass papers. Its use is, however, rather costly, owing to its solubility in water.

Heavy spar, blanc fix (barium sulphate), is one of the most useful loading materials, giving the paper very valuable properties. It may be added either in form of a paste, or better, it may be precipitated in the pulp by decomposing barium chloride with Glauber's salt.

Agalite, which consists essentially of magnesium silicate, possesses a fibrous structure similar to that of asbestos. It imparts a soapy feel to papers and gives an excellent finish. Owing to its fibrous structure nearly the whole amount of this material added is carried by the pulp.

Starch. As already mentioned under sizing, starch is frequently used together with the rosin soap; it is, however, quite safe to count it among the loading materials. A large portion of the starch added to the pulp is lost; but, although expensive, its use for high-class papers cannot be dispensed with.

The feel of papers loaded with starch is not unlike that of tub-sized papers; they do, not, however, possess the characteristic waterresisting properties of the latter.

COLOURING.

The last process which is conducted in the beater consists in dyeing the paper in the pulp. The paper fibres, being nearly exclusively of vegetable origin, show much less affinity towards colouring matters than do the animal fibres, wool and silk. On account of the minute state of division of the fibres in the pulp, colours are, however, generally speaking, much more readily taken up than

is the case in the dyeing of the same fibres in the form of yarn or cloth.

To

The affinity of the various fibres towards colouring matters differs considerably, a factor to be taken into consideration in the manufacture of coloured paper which consist of a mixture of various kinds of fibres. secure a level appearance of the surface of papers of this description, mineral loading materials or mechanical wood pulp are added, the contrast of shade being thus considerably reduced. The colouring matters used in the dyeing of paper pulp may be conveniently divided into two groups, namely, the substantive, and the adjective colours. The former dye fibres direct, that is without the application of a mordant, whilst, when the latter are used a previous mordanting of the fibres is necessary to ensure fixation.

In the manufacture of cheap coloured papers, the rosin size added to the pulp may be considered as the natural mordant for many colours. The finely divided rosin, which surrounds the fibres, acts in these instances as a fixing agent.

The mordants most commonly used in paper dyeing are alum and aluminium sulphate. Their application is very simple, and they possess a remarkable affinity towards many colouring matters. Iron salts, such as ferrous sulphate, nitrate of iron, and acetate of iron are used in the dyeing of greys, blacks, and other dark shades and in the manufacture of Prussian blue, a colour very much in demand for paper dyeing.

Tannic acid is a very valuable mordant; with iron mordants it produces useful greys, which may be conveniently used as a bottom for other colours. Tannic acid, employed either by itself or neutralised, or precipitated with tartar emetic, is the best fixing agent for the basic aniline colours, such as magenta, methylene blue, &c.

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The principal colouring matters which are used in the dyeing of paper pulp may now be briefly reviewed, classifying them for this purpose into 'inorganic" and "organic colours." Of the former class, the natural mineral colours also called earth colours, are still very extensively used on account of their cheapness and their property of acting both as colouring and loading materials. The various brands of iron ochre, the oxide red, caput mortuum, umber, sepia, green earth, mineral black, China clay and pearl hardening, are amongst the principal representatives of this class.

The artificial mineral colours may either be prepared outside the beater and then added to the pulp, or the precipitation of some of these colours may be actually effected in the beater. Wherever convenient preference should be given to the latter method, the precipitation of the colour as well as the fixing being partly accomplished in the fibres.

Some of the most important paper colours belong to this group, the principal representatives of which are-iron buff, manganese bronze, chrome yellow and orange, Prussian blue, ultramarine and smalts.

The other group of colours with which we have to deal next are the organic colours. They may be sub-divided into "natural organic colours," that is colours of vegetable and animal origin, and “artificial colouring matters" usually called "coal tar colours." Many of the colours belonging to the former group have been superseded by the artificial products which are more easily appplied and which may be obtained in a more concentrated form.

Of the natural organic colours, annatto, turmeric, safflower, red wood, cochineal, weld, and others, are now, practically speaking, of historical interest only. Amongst such colours as are still extensively used, are logwood, and in combination with it, fustic extract, for cheap blacks and greys; also catechu or cutch for fast browns or as a bottom or a mordant for dyeing heavy shades with aniline colours.

The artificial organic colouring matters now at the disposal of the paper-maker are very numerous. Their characteristics are brilliancy and purity of shade, strength, easy application, and solubility in water. Fastness to light and air is, however, with few exceptions, not their strong point.

Time will only permit me to mention the chief representatives of the various classes. Of the yellows and oranges we have auramine, metanil yellow, naphthol yellow, orange II. and chrysoidine; of the browns-Bismarck brown and vesuvine; of the blues-water blue, Victoria blue, and methylene blue; of the reds-the eosines, rhodamines, palatine scarlet, saffranine, and magenta; of the violets-methyl violet and crystal violet; of the greens— brilliant green and malachite green; and of the greys-the nigrosines.

The application of colours to the pulp is, however, not restricted to coloured papers. Nearly all whites have to be produced by adding small quantities of colours. The natural shade of the bleached pulp is counteracted by a