20 to 30 parts finely blended copper (made by reduc lion of oxide of copper with hydrogen or precipitation from solution of its sulphate with zinc) are made into a paste with oil of vitriol. To this add 70 parts mercury and trit urate well; then wash out the acid with boiling water and allow the compound to cool. In 10 or 12 hours, it becomes sufficiently hard to receive a brilliant polish and to scratch the surface of tin or gold. When heated it becomes plastic, but does not contract on cooling.

Alloy, "Oroide." This is made of pure copper 100 parts, tin 17 parts, magnesia 6 parts, sal ammoniac;; parts, quicklime parts, tartar of commerce 9 parts. The copper is first melted, then the magnesia, sal-ammoniac, lime, and tartar in powder are added little by little and briskly stirred for half an hour. The tin is lastly mixed in grains until all is fused. The crucible is covered, and the fusion maintained for 35 minutes, when the dross is skimmed off and the alloy is ready for use.