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).

10

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 bo part; for assays of gold from gramme (7.71 grains) as the unit = 1000 parts to part.

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 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 denar, 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 × 7000=14,000,000 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.]

VI. Tools and Implements.

19. GENERAL REMARKS.

We will only consider the tools and implements required for the dry method, as those for the wet method1 do not differ from those used in analytical chemistry (stands, forceps, crucible tongs, cork drill, etc.).

20. FURNACE TOOLS.

The following tools are used in attending the furnaces. Shovels with perforated blades for handling the fuel; large and small iron pokers and scrapers for cleansing the grate and muffle, poking the coal, etc.; coal and ash sieves with meshes respectively 1 centimeter (0.39 inch) and 3 millimeters (0.11 inch) wide; iron boxes filled with water for cooling the tools, etc.

21. IMPLEMENTS.

The following are required:

A. For preparing the assay sample.

1. Sampling.-Iron spoons having a diameter of 4 centimeters (1.57 inches); shovels; troughs, wooden boxes, etc., for the reception of the assay samples; files and cold chisels; hollow chisels; drills; hollow cylinders of sheet iron for small ore; magnifying glass, etc.

2. For drying the samples (p. 26).—Drying pans of sheet iron or copper; drying frames; iron spatulas ; dry

1 Neuere Geräthschaften in Fresenius' Ztschr. f. analyt. Chemie.

ing disk (Fig. 2, p. 26); water-baths (Fig. 1, p. 26); airbaths; desiccators (Fig. 17a, p. 43), etc.

3. For comminuting the samples (p. 27).—Grinding plate and rubber; mortars; hammers; anvils; rolls; common scissors and plate shears; files; rasps; pliers;

rise, etc.

4. For sifting.-A series of sieves of from 20 to 100 meshes to the inch, for sifting ores, fluxes, etc. A box sieve, consisting of a round tin box, into which a sieve can be snugly fitted, is very useful, as in sieving the pulverized ore there is no dust. If desired, a tin cover can be made to inclose the whole.

5. For washing (p. 28).—Beaker glasses; glass cylinders; wooden vanning troughs (Fig. 4, p. 29), etc.

6. For weighing.-Brass pincettes with fine ivory points for taking up small weights, metal buttons, etc., and others with blunt or broad points for lifting larger weights and heavier buttons of precious and base metals; brass mixing spoons, 18 centimeters (7.08 inches) long and 2 centimeters (0.78 inch) wide, having on one end a spatula 1.2 centimeters (0.48 inch) wide; camel's hair and bristle brushes; watch-crystals; small glass or porcelain vessels ; glass tubes, one end fused shut and the other closed with a cork or glass stopper; glazed paper; artistically closed cornets of fine letter paper of different colors. They are used for the reception of shavings, granules, etc., of alloys, etc.

7. For charging.-Mixing scoops (Figs. 6 and 6a, p. 32); mixing spatula of brass or horn; bristle brushes; measuring spoon for granulated lead; touch stones and touch needles, etc.

B. Implements for transporting the assaying vessels and for manipulating the same in the furnace.-Iron tongs (Fig. 46) for catching hold of the vessels. For large muffle-furnaces they are 80 to 100 centimeters (31.49 to