METHOD OF MANUFACTURE. The familiar lead pencil of every-day use consists of a round or polygonal stick of graphite mixed with clay, surrounded by a cedar case. The graphite is first reduced to an impalpable powder by grind ing. Water is then added and the substance is run through mixers in a fluid state, the proper amount of finely powdered clay being put into the mixture and thoroughly blended with it. A little lampblack is sometimes added to the com position to increase the blackness. The more clay used, the harder will be the pencil. The mixing is performed by specially constructed ma chinery. After thorough mixing the mass is placed in filter presses to exclude the water and reduce the mixture to a doughy consistency. The material is next passed through dies, consisting of successive plates with holes of varying di ameter. Great pressure is used, causing the mixture to ooze forth in doughy strings. This process is repeated several times. The final dies are of the same diameter as the finished lead. The graphite in this form is straightened, cut into three-foot lengths, and allowed to dry. It is next cut into pieces of the required length, usually about seven inches. These pieces arc
packed in crucibles and burned for several hours, to extract the moisture. The graphite is now ready to be inserted in its wooden case. Some times the plumbago is calcined before being mixed with clay. For some varieties of drawing pencils the leads are immersed for a minute in very hot melted wax or suet, before being mounted.
The leads are usually incased in the wood before it is shaped into a pencil. Little slabs of cedar, two, four, or six pencils wide, are passed through a machine which cuts out semicircular grooves, the diameter of the pencil. , Into the grooves in one of these slabs the leads are laid and another grooved slab is glued to it, thus completely incasing the graphite. The slabs are now passed through machines which divide them into pencils, with their sides shaped in hexagonal or curved form. After the processes of polishing. varnishing, and stamping, all of which are per formed by machinery, the pencils are ready for shipment.