Fig. 17.
Roeckner's Boiler.—This boiler, of which an illustration of two in series is given in Fig. 17, has been extensively adopted by paper manufacturers. It will be noticed that the vomit-pipe A is placed outside the boiler, and the steam enters at the cock B, forcing the liquor up the vomit-pipe A and distributing it over the esparto. A pipe C is used for heating the liquor by means of waste steam at the commencement of the operation. The grass is fed into the boiler at the opening D. At E E are gauges for showing the height of the liquor in the boiler, F F F are pipes for the supply of steam, strong ley, and water, and the door G is for the discharge of the boiled grass. Each boiler is capable of holding 3 tons of esparto, and the boiling is completed in about two and a half hours, at a pressure of from 35 to 40 lbs. per square inch. It is said that the boiler effects a saving both in time and the amount of soda used.
Mallary's Process.—By this process the inventor says that he obtains the fibre in greater length, and gets rid of the gummy and resinous matters in a more economical way than by the present system. The materials used form a species of soap, with which and with the addition of water, the esparto is boiled. To carry out his process, he places in a boiler a suitable quantity of water, to which caustic soda, or a ley of the required strength to suit the nature of the fibre, is added; magnesite, or carbonate of magnesia, in the proportion of about 2 per cent. of the fibrous material, or a solution of sulphate of magnesia, is then added and mixed with the ley. He next adds "an improved saponaceous compound" to produce the required result, and when the boiling is completed, the stuff is treated as ordinary stock, to be applied for paper-making or other uses. The proportions are as follows:—2 gallons of petroleum or its products, 1 gallon of mustard oil, 10 to 15 lbs. of caustic soda, and 1 per cent. of boracic acid. These are placed in a copper and heated for 1 to 2 hours, until properly saponified. From 3 to 6 gallons of the "saponaceous compound" are added to the ley and magnesite, previously placed in the boiler with the fibre, and the boiling is kept up for the usual length of time, when the fibre will be found "beautifully soft, and the greater portion of the gum, silica, and resinous matters removed, or so softened as to be no hindrance to the perfect separation of the fibres, whilst the strength, silkiness, and softness are preserved in all their natural integrity." Considering that caustic soda ley "of the required strength" forms an essential part of this process, we should imagine that the auxiliaries mentioned would scarcely be necessary.
Carbonell's Process.—In this process, devised by M. Carbonell, of Paris, 200 lbs. of raw esparto are placed in a wooden vat furnished with a perforated steam-pipe, 20 lbs. of soda and 30 lbs. of quicklime being mixed with it: the vat is then supplied with cold water until the esparto is completely covered. Steam is then turned on, and the materials boiled for 4 hours. The spent liquor is then drained off, and the esparto submitted to hydraulic pressure. It is afterwards washed and broken in a rag engine, and in about 15 minutes is reduced to half-stuff. 20 lbs. of chloride of lime dissolved in water are then introduced, and the cylinder kept in motion as usual. In another vessel, lined with lead, 1¼ lb. of sulphuric acid is dissolved in 3 lbs. of water, and this gradually added to the pulp, which immediately assumes a reddish colour; but in the course of about three quarters of an hour it becomes perfectly white, when the pulp is ready for the paper-maker.
In the boiling of esparto, several important points have to be considered. The kind of esparto to be treated is the first consideration, since this grass differs materially in character in the different countries from which it is imported. Spanish esparto is considered the best for paper-making, as it is stronger in fibre and yields a whiter pulp than other varieties. Of the African espartos there are several varieties, which are known respectively as Oran, Tripoli, Sfax, Gabes, and Susa. Of these, the first-named (Algerian esparto) is held in highest estimation amongst paper-makers, since it more closely resembles Spanish esparto than the other varieties, though not so hard and stiff as the latter. These grasses usually have a length of about 10 to 12 inches. Tripoli esparto has an entirely different growth, being sometimes as long as 2½ or 3 feet, and proportionately stouter, and is also softer than Oran esparto, which is not so hard as the Spanish variety. Tripoli esparto does not yield a strong paper by itself, but in conjunction with Oran esparto gives more favourable results. Sfax and Gabes espartos have a closer resemblance to Oran than Tripoli, but are not so strong as Oran, being green and spongy, and not so dry as the latter variety. Susa esparto of good quality is said to equal Oran, but not to yield so high a percentage of fibre.
The next important consideration is to determine the percentage of caustic alkali which should be used per hundredweight of the particular variety of esparto to be treated, and we cannot do better than give the following proportions recommended by Mr. Dunbar.
| Fine Spanish | 18 to 20 | lbs. of | 70 per cent. | caustic soda | per cwt. |
| Medium Spanish | 16 to 18 | " | " | " | " |
| Fine Oran | 18 | " | " | " | " |
| Medium Oran | 16 to 17 | " | " | " | " |
| Susa | 18 | " | " | " | " |
| Tripoli | 19 to 20 | " | " | " | " |
| Sfax | 20 to 21 | " | " | " | " |
Mr. Dunbar says that the above figures "insure a first-class boil, with the steam pressure of 25 lbs. and not exceeding 30 lbs., but are liable to alteration according to circumstances—such as the form of boilers, quality of the water for boiling purposes, and steam facilities, which ought at all times to be steady and uniform to get the absolute regularity required."