meters (3.14 inches) wide on the top, and 50 millimeters (1.96 inches) on the bottom, have a clear height of 74 millimeters (2.91 inches), and a total height of 90 millimeters (3.54 inches).

Soapstone crucibles, if gradually heated, are adapted for all smelting purposes. They are infusible, not affected by alkalies, and become harder by burning.

Fig. 42.

2. Vessels with feet. Crucibles for lead and copper smelting (a, Fig. 42). -The latter are more refractory than the first. They are 25 to 32 millimeters (0.98 to 1.25 inches) wide on the top, 40 to 50 millimeters (1.57 to 1.96 inches) in the centre, 83 to 85 millimeters (3.26 to 3.34 inches) high in the clear, with a total height of 110 to 120 millimeters (4.32 to 4.71 inches). Sometimes there is a depression in the bottom for the reception of the regulus, and the foot, when broken off, may serve as a cover.

a

Fig. 43 shows a crucible for smelting iron, lined with powdered charcoal (see above). These crucibles are 45 millimeters (1.76 inches) wide, and 55 millime

ters (2.16 inches) high in the clear, with a total Fig. 43. height of 90 millimeters (3.54 inches).

3. Other clay vessels.-In this category belong muffles (p. 49), retorts, and tubes.

B. Wrought-iron vessels. Crucibles for assay

of lead, with or without lip.—These are from 8 to 12 centimeters (3.14 to 4.72 inches) high, and 5 to 8 centimeters (1.96 to 3.14 inches) wide. The sides are from 10 to 12 millimeters (0.39 to 0.47 inch) thick, and the bottom from 2 to 3 centimeters (0.78 to 1.18 inches). Other iron vessels used are, tubes and retorts, and cast-iron muffles.

C. Vessels of bone-ash: Cupels (Fig. 44).-They are

Fig. 45.

B

made either of bone-ash alone, or with an addition of a little wood-ashes, or pearl-ash, to the water Fig. 44. used for moistening the bone-ash, which addition decreases their power of conducting heat. The bones are burnt white throughout, are then powdered and washed. The dried powder, which should be about as fine as coarse wheat flour, is used for the principal mass, while a finer flour is reserved for a final coating. The cupels are formed by filling and driving the prepared bone-ash into a mould made for the purpose (Fig. 45), B, the pestle; A, the mould; or they are pressed.1 Ordinary Freiberg cupels for ores consist of 3 volumes soap-boilers' ash, and 1 volume bone-ash. Their outer diameter is 35 millimeters (1.37 inches), diameter in the clear 24 to 25 millimeters (0.94 to 0.98 inch). They are 10 to 12 millimeters (0.39 to 0.47 inch) high in the clear, with a total height of 18 millimeters (0.7 inch). Fine or mint cupels consist of 2 volumes soap boilers' ash, and 3 volumes bone-ash. Their total diameter is 26 millimeters (1.02 inches), with a clear diameter of 18 millimeters (0.7 inch); their total height is 14 millimeters (0.55 inch). Cupels in order to be perfect should dry very slowly, and be thoroughly ignited before they are used. They should be white, and, besides a certain degree of solidity, should possess the requisite porosity to absorb litharge (when taken up with the tongs they must not crumble, but it should be possible to crush

A

1 B. u. h. Ztg. 1868, p. 154.

them with the fingers). They must neither undergo any perceptible change, nor crack, when exposed to a white heat, and should develop no gases and form no chemical combinations with the substances fused in them. When too solid they crack easily, absorb the litharge too slowly, cupellation being thereby prolonged, which causes a loss of silver. If, on the other hand, they are too porous, they absorb too much silver and gold with the lead oxides. (A loss of metal can never be entirely avoided in the assay.)

D. Vessels of other materials.-Cupels in the form of a prism about 2.5 centimeters (0.98 inch) high and 4 centimeters (1.57 inches) thick are chiselled out of charcoal, or turned from hard wood and then carbonized. Coke cupels are made of powdered and sifted coke, which is kneaded with liquid pitch. The stiff mixture formed after the mass has become cold, is pulverized, and some more powdered coke added to it (4 parts of coke to 1 part of pitch). The entire mass is then passed through a hair sieve, heated, and stamped in a cupel-mould about 2.5 centimeters (0.98 inch) high, with a diameter of 3.7 centimeters (1.45 inches) on the top and 3 centimeters (1.18 inches) on the bottom. The finished cupels are then ignited, the air being excluded during the operation.

16. ASSAY VESSELS FOR THE WET METHOD.

1. For assays by gravimetric analysis.-Articles of glass: digesting-flasks or matrasses, beaker-glasses, funnels, watch-glasses, wash-bottles, stirring-rods, retorts, tubes, apparatus for generating sulphuretted hydrogen, etc. Of porcelain : crucibles, evaporating dishes, tubes,

etc. Of other materials: forceps, crucible tongs, wire triangles, wire gauze, etc.1

2. For assays by volumetric analysis, see p. 43.

3. For assays by colorimetric analysis.-Tapering glasses or tubes of a uniform diameter for comparing colors; graduated measuring vessels of glass or porcelain, divided into centimeters, ounces, etc.; dissolving vessels, etc.

V. Balances and Weights.

17. BALANCES.

Of these will be required

1. An ore balance, for weighing ores and the regulus of base metals. This should be capable of carrying from 30 to 50 grammes (1.05 to 1.76 ounces), and, with 5 grammes (77.19 grains) in each pan, must be distinctly sensitive to an addition of 1 milligramme (0.015 grain).

2. Bullion or button balance, inclosed in a case, for weighing gold and silver beads and alloys of precious metals. It should be capable of carrying 5 grammes (77.19 grains) at the utmost, and must distinctly turn with to milligramme when both pans are loaded with 1 gramme (15.43 grains).

3. An apothecary balance, for weighing larger quantities. It should be sensitive to 5 milligrammes (0.077 grain).

4. A rough scale, for weighing approximately larger quantities (fluxes, etc.). A grocer's scale will answer the purpose.

Dreiecke und

1 Muencke's Klemmvorrichtung in Dingler, ccxxv. 387. Tiegelzangen mit Porzellanarmirung in Fresenius' Ztschr. 1879, p. 259. Doppelaspirator, Dingler, ccxxv. 619.

18. WEIGHTS.

The following are used:—

1. The gramme weight, from 50 to 0.001 gramme (771.61 to 0.015 grains); for silver coins from 1 gramme (15.43 grains)=1000 parts to Tobo part; for assays of gold fromgramme (7.71 grains) as the unit = 1000 parts to part. 10‰ō

2. Centner.-1 assay centner = 5 grammes (77.19 grains) (Upper Harz) or = 3.75 grammes (57.89 grains) (Freiberg) = 100 pounds, which is divided into 100 parts of pounds, or the quint, the smallest weight being 1⁄2 of the quint.

=

=

=

In Austrian smelting works, etc., 1 assay centner = 10 grammes (154.38 grains), which is divided into 100 parts, called pounds; the pound is divided into 32 loth, the loth into 4 quentchen, and this into 4 denär, the smallest weight being 1 denär — 0.195 milligramme (0.003 grain).-English grain weight. The unit is usually 1000 grains (64.8 grammes). The smallest weight for gold and silver buttons is 0.001 grain. For an assay of ore, generally a sample is taken weighing 400 grains. The divisions of this system are as follows: 1 ounce 480 grains 20 pennyweights (24 grains to the pennyweight).-American assay weight. 1 assay ton 29.166 grammes (450.26 grains); 1 pound avoirdupois (commercial weight) = 7000 troy grains (apothecaries' weight); 1 ton 2000 pounds avoirdupois; 2000 700014,000,000 grains troy in 1 ton avoirdupois; 480 grains troy : 1 ounce troy; 14,000,000 480=29,166 troy ounces in 2000 pounds avoirdupois; one assay ton contains 29,166 milligrammes, therefore, 2000 pounds are to 1 assay ton as 1 ounce troy weight to 1 milligramme (0.015 grain). If, for instance, an assay ton yields 1 milligramme (0.015 grain) of gold or silver, the result will be 1 ounce troy in 2000 pounds avoirdupois without further calculation.

÷

[For general practice, it is far preferable to use the French metric system of weights, instead of the arbitrary and varying German systems. The simplicity and convenience of the American assay ton leaves nothing to be desired.-TRANSLATOR.]