Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/512

 490 p E N P E N brushes used by artists, has, in English, come commonly to signify solid cones or rods of various materials used for writing and drawing. Some method of producing black or coloured markings with rods of solid material on parchment, paper, wood, and other like smooth surfaces must have been known from time immemorial, but the ordinary so-called black-lead pencil does not possess a very high antiquity. It has been asserted that a manuscript of Theophilus, attributed to the 13th century, shows signs of having been ruled with a black-lead pencil; but the first distinct allusion to the common form of the instrument occurs in the treatise on fossils by Conrad Gesner of Zurich (1565), who describes an article for writing formed of wood and a piece of lead, or, as he believed, an artificial composition called by some stimmi anglicanum (English antimony). The famous Borrowdale mine in Cumberland having been discovered about that time, it is probable that we have here the first allusion to that great find of graphite which for so long supplied the world with its best lead pencils. While the supply of the Cumberland mine lasted, the material for the highly-esteemed English pencils consisted simply of the native graphite as taken from the mine. The pieces were sawn into thin veneers, which again were cut into the slender square rods forming the &quot;lead&quot; of the pencil. These leads were either cased in pencil cedar (the wood of the Virginian cedar, Juniperus virginiana), forming ordinary pencils, or they were, by an ingenious and delicate process of turning, in which ruby-cutters were used, rendered circular to supply the &quot;ever-pointed pencils,&quot; which, however, are of comparatively modern origin. Strenuous efforts were made on the Continent and in England to enable manufacturers to become independent of the product of the Cumberland mine. In Nuremberg, where the great pencil factory of the Faber family was established in 1761, pencils were made from pulverized graphite cemented into solid blocks by means of gums, resins, glue, sulphur, and other such substances, but none of these preparations yielded useful pencils. About the year 1795 Conte of Paris devised the process by Avhich now all black-lead pencils, and indeed pencils of all sorts, are manufactured. In 1843 Mr Brockedon patented a process for compressing pure black-lead powder into solid compact blocks by which he was enabled to use the dust, fragments, and cuttings of fine Cumberland lead. He sub mitted the powdered substance to enormous pressure, and, by concurrently exhausting the air from the dies and the block of graphite in process of compression, he succeeded in forming a dense compact and uniform cake which could be treated in the same way as natural massive graphite from the mine. Brockedon s process would have proved successful and important had the supply of fine English black lead continued, but the exhaustion of the Borrowdale supplies and the excellence of Conte s process have rendered it more of scientific interest than of commercial value. The pencil leads prepared by the Conte process consist of a most intimate mixture of graphite and clay, both first brought to a con dition of the finest subdivision. The graphite is reduced to fine powder in a mortar ; it is sifted and sometimes treated with mineral acid, to free it from iron, &c., then washed, and thereafter calcined at a bright-red heat. To get it in the condition of fine division, it is mixed with water and poured into a vat, where the heavier particles sink. From this vat the water bearing the lighter particles passes into another at a lower level, and so into one or two more, in each of which the comparatively heavy particles sink, and only the still finer particles are carried over. That which sinks in the last of the series is in a condition of extremely fine division, and is used for pencils of the highest quality. The clay, which must be free of sand and iron, is treated in the same manner, and brought to a state of great uniformity and smoothness. Clay and graphite so prepared are mixed in varying proportions from about equal parts to two of day for one of graphite according as the pencils are to be hard or soft. They are thoroughly incorporated and ground to gether, then placed in bags and squeezed in a hydraulic press till they have the consistency of stiff dough, in which condition they are ready for forming pencil rods. For this purpose the plastic mass is placed in a strong xipright cylinder of brass, into which a plunger or piston works, moved by a powerful screw-press. The bottom of the cylinder consists of a thick bronze plate having in it a number of small apertures the section and size of the leads to be made. By the application of pressure to the plunger the graphite mixture is squeezed in continuous threads through the holes, and these threads are received and arranged in straight continuous lengths on a board, on which they are left to dry for some hours. For further drying by gentle heat they are placed in straight grooves in a grooved board, covered with another board, in which position they harden to stiff rods. These arc afterwards cut into lengths for pencils, which are packed with charcoal in a covered crucible and submitted to a high furnace-heat. The tvo elements which regulate the comparative hardness and blackness of pencils are the proportions of graphite and clay in the leads and the heat to which they are raised in the crucible. According as the proportion of graphite is greater and the heat lower the pencil is softer and of deeper black streak. The cedar in which pencils are cased is cut into two sets of rectangular slips of unequal thickness ; but so that a thick and a thin slip put together form in section a square. In the thick or body piece is formed the groove or depression to receive the lead, which perfectly fits and fills it. The thinner covering piece is glued on and the pencil rounded between revolving cutters working at great speed. The cutters leave the rounded surface perfectly smooth, and it only remains to stamp the finished pencil with name and grade, &c. Very many pencils but not usually good English qualities are lacquered or varnished, and have the names, &c., stamped in gold letters. Black pencils of an inferior quality are made from the dust of graphite melted up with sulphur and ran into moulds. Such, with a little tallow added to give them softness, are the pencils commonly used by carpenters. Coloiired pencils consist of a mixture of clay, with appropriate mineral colouring matter, wax, and tallow, treated by the Conte method as in making lead pencils. In the indelible and copying pencils which have come into use in recent years, the colouring matter is an aniline preparation mixed with clay and gum. The mixture not only makes a streak which adheres to the paper, but, when the writing is moistened w : ith water, it dissolves and assumes the appearance and properties of an ink. Nuremberg is the great centre of the pencil trade, possessing twenty-six factories which give employment to 5500 persons, the annual output of pencils numbering not less than 250 millions, of a value of upwards of 400,000. (J, PA.) PENDULUM. See CLOCKS, vol. vi. p. U, and MECHANICS, vol. xv. pp. 705, 718, 768. PENELOPE, the faithful wife of the Greek hero Odys seus (Ulysses), immortalized by Homer in the Odyssey. She was the daughter of the Spartan Icarius and Peribcea. Shortly before Odysseus left his native island of Ithaca to war against Troy, Penelope bore him a son, Telemachus. When her husband tarried long many chieftains of Ithaca and the islands round about wooed her to wife ; they behaved wantonly, wasting the substance of Odysseus, insulting his son, and corrupting the maidservants. The heart of Penelope yearned for Odysseus, and, to rid herself of the importunities of the wooers, she bade them wait till she had woven a winding-sheet for old Laertes, the father of Odysseus. But every night she undid the piece which she had woven by day, so that the web was always un finished. This she did for three years, till her maids revealed the secret to the wooers. Eobbed of her pretext for delay she was in sore straits, till she was relieved by the arrival of Odysseus after an absence of twenty years. He slew the wooers, and the long-parted husband and wife were united once more. Such is the story of Penelope in Homer. Later writers add other particulars about her. She was won by Odysseus in a race proposed by Icarius to his daughter s suitors. When Icarius would fain that Odysseus should bide with him in Sparta, or at least leave him his daughter, and Odysseus let Penelope choose whether she would go with him to Ithaca or stay with her father in Sparta, she silently drew her veil over her fiace. Her father understood her and let her go (Pausan., iii. 12, 20). Some said that she bore a son, Ptoliporth.es, to Odysseus after his return from Troy. Others (mar ring Homer s picture of her as a true and loving wife) said that in her husband s absence she bore Pan to Hermes or the suitors. Another story was that on his return Odysseus repudiated her as