. A manual of mechanical dentistry and metallurgy . into a clean crucible lined on the insidewith borax, and placed in the furnace. As soon as themetals are fused, the crucible should be removed and thecontents poured cjuickly but carefully into the ingot-molds;the latter being conveniently near the furnace, as the moltenmetals soon become chilled on exposure to the open pouring, the molds, if made of iron, should be mod-erately heated and oiled, or coated with lamp smoke byholding their inner surfaces over the fiame of an oil lampor gas-jet. 20 S MECTTANICAL DENTISTRY AND METALLURG
. A manual of mechanical dentistry and metallurgy . into a clean crucible lined on the insidewith borax, and placed in the furnace. As soon as themetals are fused, the crucible should be removed and thecontents poured cjuickly but carefully into the ingot-molds;the latter being conveniently near the furnace, as the moltenmetals soon become chilled on exposure to the open pouring, the molds, if made of iron, should be mod-erately heated and oiled, or coated with lamp smoke byholding their inner surfaces over the fiame of an oil lampor gas-jet. 20 S MECTTANICAL DENTISTRY AND METALLURGY. Ingot-molds.—Aarions sul)stanccs are used for the con-struction of ingot molds, Ijut those in most common use aremade of iron, and, for gold, are generally about two inchessquare and from ^ to ,• of an inch thick (Fig. 174). Theyshould be slightly concave on their inner surfaces, to com-pensate for the greater shrinkage of the gold in the centerthan at the margins of the ingot. Soapstone is sometimes employed for the same purpose, Fig. and is preferred by some. Molds made from this substanceshould also be warmed and oiled before pouring the are also made from charcoal, which is highly recom-mended for the purpose, though it requires to be frequentlyrenewed. Charcoal Ingot-molds may be very easily and quicklymade. Select a close-grained compact piece of charcoal ofsuitable size, cut through it w^ith a saw% and then rub thedivided surfaces together until perfect coaptation is required size and shape of the mold is then cut out inone section of the block; the two pieces are then secured inplace by binding with wire, or with the use of clamps. Asbestos Molds.^—Comparatively inexpensive, and at thesame time more convenient and (lural)le contrivances de-signed for the same puri)ose. combining both crucible and GOLD. 209 ninld. and eni1)raciiTi^- the s])ecial advantages claimed forcharcoal, may he ohtained at the dental depots. One of thesimples
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