FURNACE OF ASSAY. Under [Assay], I have referred to a furnace constructed by Messrs. Anfrye and d’Arcet, which gives some peculiar facilities and economy to the ancient process by fire. It had originally a small pair of bellows attached to it, for raising the heat rapidly to the proper vitrifying pitch. The furnace, 171⁄2 inches high, and 71⁄2 inches wide, made of pottery or fine clay, is represented [fig. 481.], supported upon a table, having a pair of bellows beneath it. The laboratory is at b, the blow-pipe of the bellows at d, with a stop-cock, and the dome is surmounted by a chimney a, c, in whose lower part there is an opening with a sliding door, for the introduction of the charcoal fuel. The furnace is formed in three pieces; a dome, a body, and an ash-pit. A pair of tongs, a stoking hook, and cupel, are seen to the right hand, and the plan of the stone-ware grate, pierced with conical holes, and a poker, are seen to the left. This grate suits the furnace represented under [Assay]. The following are comparative experiments made by means of this furnace:
| Numbers. | Silver employed. | Lead employed. | Time of Assay. | Standards. | Charcoal used. | |||
|---|---|---|---|---|---|---|---|---|
| 1 | 1 Grain. | 4 Grains. | 12 | minutes. | 947 | millièmes. | 173 | Grains. |
| 2 | — | — | 11 | 950 | 86 | |||
| 3 | — | — | 13 | 949 | 93 | |||
| 4 | — | — | 10 | 949 | 60 | |||
Each assay was therefore performed at an average in 111⁄2 minutes, and not much more than a quarter of a pound of charcoal was used. An experiment of verification in the ordinary assay furnace showed the standard to be 949 thousandths.
This furnace becomes a very convenient one for melting small quantities of metals in analyses, by removing the muffle, and closing the several apertures with their appropriate stoppers. A small pedestal may be then set in the middle of the grate, to support a crucible, which may be introduced through the opening h. Coak may also be used as fuel, either by itself or mixed with charcoal. For descriptions of various furnaces, see [Assay]; [Beer]; [Copper]; [Evaporation]; [Iron]; [Metallurgy]; [Ores]; [Silver]; [Tin]; &c.
FUSIBILITY. That property by which solids assume the fluid state.
Some chemists have asserted that fusion is simply a solution in caloric; but this opinion includes too many yet undecided questions, to be hastily adopted.
Fusibility of Metals, as given by M. Thenard.