Second process for making artificial pencils, somewhat different from the preceding

—All the operations are the same, except that some lamp-black is introduced along with the plumbago powder and the clay. In calcining these pencils in the crucible, the contact of air must be carefully excluded, to prevent the lamp-black from being burned away on the surface. An indefinite variety of pencils, of every po ible black tint, may thus be produced, admirably adapted to draw from nature. Another ingenious form of mould is the following: Models of the pencil-pieces must be made in iron, and stuck upright upon an iron tray, having edges raised as high as the intended length of the pencils. A metallic alloy is made of tin, lead, bismuth, and antimony, which melts at a moderate heat. This is poured into the sheet-iron tray, and after it is cooled and concreted, it is inverted, and shaken off from the model bars, so as to form a ma of metal perforated throughout with tubular cavities, corresponding to the intended pencil-pieces. The paste is introduced by pre ure into these cavities, and set aside to dry slowly. When nearly dry, the pieces get so much shrunk that they may be readily turned out of the moulds upon a cloth table. They are then to be completely desiccated in the shade, afterwards in a stove-room, next in the oven, and lastly ignited in the crucible, with the precautions above prescribed. M. Conté recommends the hardest pencils of the architect to be made of lead melted with some antimony and a little quicksilver. In their further researches upon this subject, M. Conté and M. Humblot found that the different degrees of hardne of crayons could not be obtained in a uniform manner by the mere mixture of plumbago and clay in determinate doses. But they discovered a remedy for this defect in the use of saline solutions, more or le concentrated, into which they plunged the pencils, in order to modify their hardne , and increase the uniformity of their texture. The non-deliquescent sulphates were preferred for this purpose; such as sulphate of soda, . Even syrup was found useful in this way.