Coke, the material from, which the ordinary lighting and battery carbons are made, is usually a by-product of the process of petroleum oil refining, being the solid that remains in the stills after the oils have been evaporated. Coke carbon obtained from other sources can of course be employed for the purpose. The coke is in the form of irregular chunks of black porous material, somewhat lighter than coal-coke, and is ground in a vertical bark mill to what is known as pea-size, and, by means of belt elevators, is taken to large iron storage tanks above the retorts, being drawn from there into small iron cars which run along the top of the retorts, and discharge their contents directly into the calcining ovens. Here the coke is subjected to a high temperature by the burning of coal gas, the ovens being kept closed; all the volatile matter and other impurities are consumed.the residuum being pure carbon. After cooling to a certain degree, the doors are opened and the material is hauled out; it falls into a metal trough in front of the retort, a link belt couveyer in the trough conveying the carbon to an elevator. This raises the material and allows it to fall through flexible chutes, which deliver it in even layers over a floor, where it is left to cool.

The carbon, when cool, is passed through grinding mills, either vertical or horizontal; the latter resemble the burr-stone mills employed in grinding grain. The powdered carbon is separated into different grades in a set of bolting machines, the coarser grades being afterwards re-ground. Following the bolting process, the material is delivered to a number of steam-heated revolving iron barrels or boxes, in which the carbon powder is incorporated with the binding material; this is prepared by a special process and is ground and bolted in much the same manner as is the carbon. Being suitably mixed, the material is got ready for the moulding or forcing process. In the shaping of the arc-lamp carbons and battery plates, one of two processes is followed; one is known as the moulding process, and the other as the forcing. In the former the material is carefully weighed, and then placed in the moulds, which consist of grooved plates of steel containing from twelve to eighteen forms, depending upon the diameter of the pencils to be moulded. Ihe material is carefully packed and adjusted, and then smoothed off with a straightedge, and the second or upper part of the mould is then pressed upon the lower one.

The tilled moulds are placed on endless chains, which convey them in the direction of the hydraulic presses. Before reaching the latter they are led over a slow-running conveyer which passesthrough a gas-heated furnace; on emerging from this the moulds are placed upon the head of the vertical plungers of the presses. After having been subjected to great pressure, they are released and the formed pencils, which are held together by a thin web of material, are removed and placed on a corrugated pan. The moulds must be oiled before refilling. The pencils are held straight on the corrugattd pan until cool, when they are broken apart by hand and fed one at a time into the strippers, which automitically draw them through very rapidly and shave off the portions of the web that may adhere to the sides of the pencils. The scrap is returned to the mills to be ground and treated again. Before describing the baking process through which the pencils next pass, the forcing method of forming the pencils must be touched upon.

The mixture of powdered carbon and binding material is hydraulically pressed into compact cylinders, and these are fed, one at a time, into the Jumbo presses; in these large cylinders are plungers, which force the material through dies, upon the size of which must of course depend the size of the resultant pencils. The material is forced out into grooved trays and broken off into lengths of about 4 ft. When cool, these are passed through a machine and further cut to the desired lengths. Pencils produced either by the moulding or the forcing method are baked in the same manner, being carefully piled in the firebrick furnaces in regular rows; a small thickness of carbonising material is placed between each layer of pencils. When the furnace is full it is covered with a kind of clay that vitrifies in the baking process and, covering the bed with a scale, prevents the gas employed as fuel coming in contact with the carbon pencils. The baking lasts for eight or ten days. at the end of which time the top of the oven is removed and the pencils, when cool, lifted out with implements resembling hay-forks. The pencils for the electric arc lamps are then sorted and tested for straightness, being allowed to roll down an inclined steel plate.

Any crookedness is made apparent by light rays between the pencils and the steel plate. After being sorted into about three qualities, the pencils formed by the forcing process are pointed in machines. Cored carbons are filled with the special preparations by machinery, the material in the form of a thick metallic paint being forced into the cavity of the carbon by hydraulic pressure.