in the form of the dry powder, or in the form of a thin creamy paste, made by stirring the powder with water in tanks provided with agitators.

Engine-sizing. The sizing of the paper is also carried out in the beater, rosin size being used. The fact that the pulp is sized in the beater explains the use of the term E.S. as applied to various papers, the letters standing for the words "Engine sized."

floor level

Fig. 30.-Section of Umpherston Beating-engine.

a. Vessel containing pulp.

b. Backfall.

c. Beater-roll.

d. Regulating wheel for roll.

e. Beater-roll cover.

f. Outlet-pipe.

g. Bed-plate of stationary knives.

Sizing. The necessary amount of rosin soap, prepared as shown below, is added to the mixture of pulp and loading soon after the latter is incorporated. The soap dissolves in the water to a thin milky solution and mixes with the pulp, but does not size the fibres. The sizing is only complete when the rosin and rosin compounds are actually precipitated upon the fibres and thrown out of solution, a change which is brought about by the addition of alum to the contents of the beating-engine. The alum reacts with the soap, which consists of free rosin dissolved in resinate of soda, forming an insoluble resinate of alumina and insoluble free rosin, and these substances being in an exceedingly fine state of divison become evenly distributed through the whole mass of pulp.

It may be noted that the mere addition of rosin soap to the pulp in the beatingengine does not in itself size the paper, the process being carried out as follows:

The proper quantities of pulp and loading, if any, are put into the beater. The requisite amount of rosin soap drawn off from the store-tanks in pails is added after a short time and thoroughly incorporated by the circulation of the stuff in the engine.

A solution of alum is then poured into the beater to complete the operation, the function of the alum being to precipitate the rosin upon the fibres so as to ensure a maximum sizing effect. The nature of the change brought about by the alum may be demonstrated by pouring a small quantity of a dilute solution of alum into some rosin soap, when the milky liquid gradually becomes clear and a curdy deposit is formed, which is a mixture of free rosin and resinate of alumina thrown out by the alum. This reaction takes place in the beater, and the resinous deposit is distributed through the mass of pulp. The completion of the process does not actually take place until the paper has passed the dryingcylinders, the heat of which possibly spreads or melts the minute globules of resinous matter attached to the individual fibres.

Rosin Size. This size, which is so largely employed for common writing papers and all printing papers is made from rosin and soda ash.

Rosin, or colophony, is a brownish-coloured residue obtained during the distillation of crude turps. The turpentine exudes from certain firs and pines, and is distilled in order to separate the pure spirits of turpentine from the heavier resinous substances which are known collectively as colophony. Its colour ranges from yellow to very dark red, and the commercial product is frequently dirty, being contaminated with splinters of wood, straw and foreign impurities, which have to be carefully removed at the paper-mill.

The substances present in rosin are composed mainly of organic acids known as pinic and sylvic acids, which are insoluble in water. They are capable of reacting with alkaline substances, such as caustic soda and carbonate of soda, to form bodies soluble in water just as acids like sulphuric and hydrochloric react with alkaline substances to form salts. The salts formed in the case of rosin are called resinates; they are soluble in water and give a so-called rosin soap.

The soap is made by boiling a stated quantity of well-powdered rosin in a steam-jacketed pan for four to six hours with carbonate of soda. The alkali is put into the pan with the requisite quantity of water and boiled. The rosin is added gradually and cautiously, so as to avoid any risk of the stuff boiling over, since the mixture froths up vigorously owing to the liberation of carbonic acid.

The proportions of soda and rosin vary in different paper-mills according to requirements. If 100 lbs. of rosin are boiled with 17 lbs. of soda, the soap formed is a viscous brown transparent solution which, mixed with water and diluted, is quite clear. The rosin combines with the alkali to produce a neutral resinate of soda usually designated brown size.

Now the resinate of soda has the property of dissolving rosin. Hence the proportion of rosin may be considerably increased, but the acid size formed does not give a clear solution with water, but a milky liquid which is known as white size. If 100 lbs. of rosin are boiled with 13 lbs. of soda, an acid size, so called from the presence of an excess of rosin in the shape of rosin acids, is produced. When diluted with water, the free rosin is reprecipitated in the form of exceedingly fine globules distributed as an emulsion in the water.

A rosin soap containing a very large percentage of free rosin varying from 30 to 40 per cent. may be obtained by boiling the necessary materials under pressure in a closed vessel. The use of such a rosin size has been resorted to because it is supposed to give the best results, but on this point there is a considerable difference of opinion.

TABLE IV.

Analysis of an Acid Size, containing a small proportion of Free Rosin.

Analysis of an Acid Size containing a large proportion of Free Rosin.

Colouring. The colouring of esparto paper is usually limited to a mere toning of the natural colour of the pulp by means of a very small proportion of some aniline dye in order to produce the required shade of white. The dye is prepared

by dissolving a known weight of the solid colouring-matter in a given volume of water, an aliquot portion of the mixture being added to the beaten pulp.

Making the Paper on the Fourdrinier Machine. The pulp when properly beaten is discharged into the stuff-chests of the machine, and converted

into paper by the methods described in chap. iii., which it is unnecessary to repeat here.

There are many essential and important details in the actual manipulation of the machine which cannot be dealt with except in a larger treatise devoted to the subject of manufacture, and, moreover, an adequate appreciation of these details is only possible by a paper-maker familiar with the working of a

machine.

The paper is pressed on the press-rolls, dried on the cylinders, and partially calendered before it is reeled up.

Finishing. Esparto paper intended for writings is usually finished on the supercalenders. The partially machine-calendered paper is removed in reels from

the end of the Fourdrinier machine, taken to the finishing-room, and supercalendered.

The supercalender consists of a number of rolls, alternately chilled iron or steel rolls, and paper-bowls. The bottom roll of the stack is a heavy roll of large diameter, capable of bearing the entire weight of all the rolls in the stack. Every alternate roll is made of paper tightly compressed by hydraulic pressure on an iron spindle, the surface being turned up in a lathe perfectly true and then polished. (Fig. 31.)

As the paper passes through the stack of rolls, being in contact with the polished surfaces of metal and paper, it becomes very smooth and highly glazed.

The surface of a super

calendered paper may be improved by damping the surface of the sheet just before it enters the calender rolls. The damping is effected by means of a steam pipe provided with a number of fine jets, which throw a thin spray of wet steam on the sheet of paper.

The same effect cannot be produced by allowing the paper to come away from the drying-cylinders slightly damp. In this case, the paper is apt to get crushed in passing through the rolls, to become transparent, and considerably reduced in bulk. A little water on the surface of a dried sheet affects only the surface and not the whole bulk of the paper, so that the result of the moisture is confined to an improvement of surface.

Friction glazing.-A still higher finish can be given to all kinds of paper by the friction-glazing rolls, which are similar in general construction to the supercalender, but differ in having large paper bowls, or rolls, and small metal ones. The latter revolve at a higher speed than the former, and the paper is submitted to considerable friction. A small quantity of beeswax on the iron rolls imparts a final polish to the sheet.

Cutting. The reels of supercalendered paper are finally cut up into sheets on a cutter. Six or eight reels are mounted on suitable shafts (a, Fig. 33) at one end of the cutter, and the paper from all the reels led together over an inclined

Fig. 33.-Paper-cutter.

table (b), slit first into required widths by revolving circular knives (c), and into the required lengths by a knife which cuts the sheet at right angles (d). The slit paper passes over the edge of the inclined table, this edge being a fixed stationary steel knife (e),

and at regular intervals a heavy steel blade (d) fastened to a revolving drum comes into contact with the stationary knife and shears off the paper into proper lengths. The knives are all adjustable, so that the paper can be cut to any given size The cut sheets drop on to a travelling felt (f).

Straw Cellulose.

A fibre resembling esparto in chemical composition, but possessing physical qualities of a different order, is straw. The treatment by which the raw material is converted into straw cellulose is identical with that

used for esparto, and the process may be fitly described at this point.

The Preparation of Straw Pulp. The process in use for the manufacture of a bleached straw pulp suitable for blending with other fibres to give a fairly