Page:The American Cyclopædia (1879) Volume XIII.djvu/56

 PAPER esparto grass ; 5, wood : 6, cane ; V, jute and ma- nila. PREPARATION OF PAPER PULP. In the manufacture of paper, the first object is to pre- pare the raw materials for the processes by which they are brought into a pulpy condition. 1. Cotton and linen rags. These are placed in cylindrical machines and tossed about by long teeth fixed on revolving cylinders, an operation called thrashing. They are then sorted accord- ing to texture, fibre, and color ; next they are passed through the rag cutter, a machine which somewhat resembles a straw cutter, and are then placed in the duster, an octagonal drum covered with wire netting and revolving in a box, one end being a little elevated. After this they are usually washed preparatory to boiling. In boiling, an alkaline solution is used of varia- ble composition, according to the nature of the rags, those more highly colored, or contaminated with grease, resin, or pitch, requiring a strong lye. Ordinarily, for 100 Ibs. of rags from 6 to 10 Ibs. of carbonate of soda is used, with half as much quicklime. The lye reduces the fine hard particles of the vegetable fibre, which if allowed to remain would cause knotty places in the paper, removes much of the dust which still adheres to the rags, and partially whitens them. The solution is best heated by steam pipes. Large cylindrical iron boilers are in use in the best mills in Europe and the United States. These are provided with compartments perfo- rated with holes for draining off the water, and they are charged at the ends with several hun- dred weight of rags at a time, and then the steam is admitted under a pressure usually of about 50 Ibs. to the square inch. The opera- tion for the full charge requires from eight to ten hours, when the rags are ready for the pro- cess by which they are to be converted into pulp. This is done in what is called the engine or hollander, a Dutch invention substituted for what was previously known as the beating ma- chine. An oblong vat of the shape represented turned by a shaft resting in journals,/^. Be- neath the cylinder is a block, also armed with knives similar to those in the 'cylinder, and hav- ing very nearly the same direction, the action W d . 1. Horizontal Section of Engine. in figs. 1 and 2, in both horizonatal and vertical section, is divided longitudinally in the middle by a partition so that a continuous channel is formed, as shown by the arrows. In one side is placed a solid wooden cylinder, a, fig. 2, armed with blunt-edged knives placed longi- tudinally upon the periphery. This cylinder is FIG. 2. Vertical Section of Engine. of the two sets being such as to tear and sepa- rate the fibres. On the other side of the vat, opposite the beating cylinder, there is a hollow drum or prism of eight sides, covered at the ends with wire gauze for the purpose of discharging the water from the machine, so constructed that a slow revolution raises the water into the hollow shaft from which it is discharged. This is the general construction of the engine or hollander, and in nearly the same form it is used for three distinct purposes, washing, bleaching, and beating or reducing to pulp; and in these three uses it is respectively called the washing engine, the bleaching engine, and the beating engine. The rags are first placed in the washing engine, the knives in the cylin- der of which are not brought down so closely upon the block as in the beater, but still close enough to tear the rags and separate the fibres to a considerable extent. Water is turned in at the cock W, and the engine set in motion, the cylinder a making about 150 revolutions a minute. The rags are carried around the cir- cuit of the vat, passing beneath both cylinder and drum, the latter of which discharges the water as fast as it is received at the cock. A pipe covered with gauze in the bottom of the vat is also often used to convey away water, either during the process of washing or at its close. The washing usually takes three or four hours, when the rags are drained and placed in the bleaching engine, which differs from the other two in not having a drum for discharg- ing water, because the bleaching solution is retained in the vat till the operation is com- pleted. The bleaching, which is performed with a solution of chloride of lime, usually oc- cupies about three hours. The material is at the same time made finer, and the fibres further separated, so that they will be fitted for the action of the beating engine. The half stuff, as it is called while on its way from the washer to the beater, is then let down into cisterns to drain, after which it is carried to the beat- ing engine, and subjected to its action after the chlorine and chloride of lime and salts associated with it have been neutralized with a solution of soda or of "antichlor," a com- pound of sulphite of soda, chloride of tin, and