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and the substance rest on charcoal. When the oxide of lead is mixed with a borax-glass, it can be reduced to the metallic state, upon charcoal, with as much facility in the blue as in the bright part of the flame. Even if a piece of tin be liquefied upon charcoal in the blue part of the flame, no oxide is formed, because oxidation cannot take place when atmospheric air is excluded from the surface of a molten mass. The foregoing results avail for

some, but not for all reducing tests upon charcoal. Positive indications are attainable only in the bright part of the flame. The reducing flame is much more difficult to form than the oxidating; for this reason, the following directions must be studied.

a. The wick should not be drawn too high out of the holder, nor must it be too short; because in the first case a smoky flame would ensue, impeding reduction, from the deposition of soot upon the assay, and in the second, the substance could not receive sufficient heat, if surrounded by the luminous part of the flame.

b. To ensure exact results, have the wick evenly cut, and perfectly free from all extraneous fibres, as in the production of the oxidating flame.

C. To secure success, when the reducing flame is produced, let it be kept uninterrupted.

And lastly,

d. The operator must use great precision as to the treating of a qualitative or a quantitative analysis. For qualitative examinations, a Blowpipe with an aperture narrower than that for oxidation is employed; but for quantitative researches, which should be always performed on charcoal, a Blowpipe with an opening rather wider is necessary. As, in many qualitative analyses, the flame has often to be altered, and a different point of the Blowpipe affixed, it is better to employ a point with a narrower orifice, because, with one of too large a calibre, oxidation is more easily effected than reduction.

IV. THE SUPPORTS.

1. CHARCOAL.-When a substance requires melting, it should be exposed to the flame of the Blowpipe upon a body that will

augment the heat, without combining with the assay. The best substance to employ for this purpose is well-burned pine. It should be cut with a saw into long pieces, partly in the shape of a parallelopiped, and partly four-sided like a prism. For qualitative analysis use the long sides of the charcoal, where the annular rings are on the margin; and for quantitative use the interior part.

B

Fig. 7.

A

2. PLATINUM WIRE.-A moderately strong wire of platinum, about two inches long, and curved at one end, may be employed in many qualitative examinations with great advantage.-Fig 7, A.-The curve serves as a support in all tests of oxidation and reduction, where alteration of color only is to be observed. This support can be relied on, for it is totally free from the false variations of color which are too often perceptible when the assay rests on charcoal. In the treatment of compound metals, or in such tests of reduction where a body easily melted is to be operated upon, charcoal must, however, be used. It is necessary to have at hand several platinum wires, so as to proceed without being obliged to take off with force the glass adhering, after the extraction of the bead, or to wait for its solution in hydrochloric acid,-which is the better mode.

Should it happen that the platinum curve melts with the reagents, it must be cut away, and a new one formed. A wire can be used for a very long time, and when it becomes too short to be held between the fingers, the straight end may be fastened into a cork, or a hilt containing a box for holding the rest of the platinum wires, until any of them are required.-See Fig. 7, B.

3. PLATINUM FOIL.-The use of platinum foil in qualitative examinations is very limited, but in some cases it may be successfully employed. Foil of thin drawn platinum, a few inches long, and half an inch broad, should be selected. This metal is such a bad conductor of heat, that when the assay is exposed to the flame of the Blowpipe at one end, the other may still, without inconvenience, be retained between the fingers. Bodies in

the metallic condition which are easily fused or reduced, should seldom be tested upon platinum foil, because, from its combining with them, a hole might be produced in the metal. Should this occur, the hole can be lopped off with a scissors, and then, if the platinum be found too short, it can be easily held by forceps. Salts, or substances containing manganese, can in general be melted upon platinum foil; by this means the alkaline and earthy salts are distinguished, and the presence of manganese is recognised by the dull green color communicated to soda, upon cooling.

4. GLASS TUBES.-When the volatile ingredients contained in ores and minerals were to be ascertained, BERZELIUS employed a glass tube, from three to six inches in length, a quarter of an inch in diameter, and open at the ends. The body to be analyzed is inserted at one end, and heat applied to that part of the tube. If the compound requires only a slight degree of heat, the flame of a spirit-lamp will suffice; on the contrary, if a strong heat is necessary, the flame of the Blowpipe must be used. The volatile bodies, liberated during the roasting, sublime in the upper part of the tube, where they can be examined.

5. GLASS FLASKS.-If the quantity of water, or gaseous ingredient, contained in any substance, be required, or if a body, when heated strongly, decrepitates, a glass flask must be used, of the form of Fig. 8. If the small alembic be sufficiently wide for the free circulation of air, the vaporized bodies will be easily obtained. Flasks must not be employed in the sublimation of sulphur, arsenic, et cetera, lest combustion should ensue.

Fig. 8.

A supply of glass tubes and small flasks should always be in reserve. After the roasting has been performed in a tube, the part containing the fused substance should be removed with a file, and the remainder of the tube cleansed with the aid of a spirit-lamp and a wire enveloped in soft paper. When the tube becomes too short, one end can be sealed, and it may be used for tests of sublimation only.

6. TWO PLATINUM SPOONS.-The form of these utensils is

shown in the annexed woodcuts.

Fig, 9.

Fig. 10.

The diameter of Fig. 9 is 9-16ths, and that of Fig. 10 3-8ths of an inch. The larger spoon has a handle of platinum, joined by rivets of the same metal, which can be encased in wood; the small one, when heated, may

be held with pincers.

The first is used for melting various substances with bisulphate of potassa, and for heating gold obtained in quantitative assays; and the second, for fusing substances with nitrate of potassa. In some cases, when bodies containing water are heated with nitrate of potassa, the platinum spoon becomes tarnished with the remaining particles of metallic oxides, these may be removed, either by a drop of sulphuric acid, or by a hot solution of bisulphate of potassa. Rubbing the platinum spoon with charcoal powder is however the most effectual method of removing stains.

Fig. 11.

7. CLAY BASINS.-In quantitative determinations, basins are employed for roasting the Ores, and for the reduction of the lead and tin oxides contained in calcined and uncalcined minerals, et cetera. These dishes are formed in the following manner :- -at first a fire-proof clay is kneaded into a stiff paste with water, and then the forming surfaces of the press, which are of box-wood, —Fig. 11, A B,—are rubbed over with a paintbrush dipped in oil. The width of A at the upper part, is 7-8ths of an inch, and the depth 5-16ths; and B is constructed of a diameter smaller by the 32nd of an inch. Over the middle of the concavity of the press, place a slip of paper, three inches in length, and a quarter of an inch in breadth, and upon this a small clay ball about half an inch in diameter. Then take part B of the press, and stamp it horizontally upon the

B

A

clay mass lying in part A, as far as is required. This being accomplished, the superfluous clay will have exuded, and B can be removed easily, by careful turning. With a small knife, cut away the clay which is driven out, and then examine the margin, to learn if the basin be uniform throughout, and sufficiently thin.

Fig. 12 shows the cross section of one of these Fig. 12. basins, which is only one thirty-second of an inch thick.

If the basin be thicker in one place than in an

other, B must be applied with greater force to that part. When the basin is ready to be taken from A, the convex part of the press must be carefully removed, and then the slip of paper gently pulled, to extract the clay dish. The utensil, with the slip of paper adhering, is now put away on a stone to dry, and the press is ready for the formation of others.

An operator unused to this work will find that sometimes the basins alter in shape after leaving the mould; but this can be remedied by pressing them with the fingers upon the convex part, B.

A few hours after drying, the slip of paper falls from the clay dish. When this occurs, the basin must be heated to redness over a fire, in a potter's vessel, or in a platinum crucible over a large spirit-lamp.

In calcination, when these vessels are used, one may often serve as a lid to the other; but, for this purpose, their edges must be ground with a file.

No labor should be spared in manufacturing these basins so as to make them sufficiently thin. The clay must be made neither too stiff nor too moist; the first fault will prevent the vessel assuming a proper form, and the second endangers its falling to pieces when removed from the machine. The true consistence of the clay can be ascertained by two or three experiments.

8. CLAY CRUCIBLES. These crucibles are employed with advantage in the performance of quantitative lead assays, and in cases where the compound to be examined consists of sulphides, arsenides, and selenides. They are easily manufactured with an iron instrument, consisting of a mould and a stamp ; the mould being composed of two parts, united by a ring.

C

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