Test-fur′nace.
（Metallurgy.) One form of refining furnace for treating argentiferous alloy, such as that of lead rich in silver. It is of the reverberatory kind, a being the fire-grate, b the fire-bridge; c is the cupel or test, consisting of an oval ring of iron provided with cross-bars, into which a bone-ash mixed with water containing a small proportion of pearlash is packed, so as to form a reservoir for the molten metal. The test, when packed, is secured to an iron ring built into the masonry, and a low heat is applied to expel the moisture; this is afterward increased until the test becomes heated to a cherry red, when the argentiferous lead previously melted in another furnace is poured in. This soon becomes covered with a grayish dross, and on increasing the heat litharge begins to form. The blast is now turned on, sweeping the litharge from the surface of the alloy and over the breast, where it is received in a proper vessel. As the metal decreases in volume, more is added, and the operation continued until that remaining at the bottom of the test is sufficiently rich to be drawn off; unless this be done at the proper point, a proportion of the silver is carried off with the litharge. When all the argentiferous alloy has been thus treated, it is again subjected to cupellation in the same or a similar furnace, by which the lead is converted into litharge, the silver remaining at the bottom of the cupel, which is then allowed to partially cool, is removed from the furnace, and the plate of silver detached. See alloy; amalgamation; assay; parting; cupel.
 |
| Test-furnace. |
