ing at the same time, for instance, silica and oxide of cobalt, as in picked ores, no green is obtained with soda, but a bluishcolored mass, consisting of silicate of soda and dissolved oxide of cobalt, which perfectly destroys the reaction of manganese. But if the silica is previouly removed from the substance under examination, the slightest trace will again be perceptible. The manner of proceeding is as follows:-If the substance to be treated contains metallic sulphides and arsenides, it must be roasted and melted to a pearl, in proportion to the quantity of silicic acid, with an equal part of soda, and twice its volume of borax, on charcoal in the reducing flame. If arseniated metallic oxides are in the assay, they become reduced, and cohere, forming a readily fusible metallic globule. This is generally the case with cobalt or nickel ores, where arsenic-cobalt, arsenic-nickel, or the three metals, are obtained in combination. On cooling, the glass is separated from the reduced metallic arsenides, powdered, dissolved in hydrochloric acid, and perfectly evaporated to dryness; the metallic chlorides dissolved in water, and separated from the silicic acid by filtration; oxide of cobalt, oxide of nickel, protoxide of iron, protoxide of manganese, et cetera, precipitated from the solution by potassa, in an excess of which the alumina dissolves. The precipitate, separated by filtration, washed, and dried, is examined for manganese with soda and nitre, as already described.

§ 3. ZINC-Zn-Presence in the Mineral Kingdom, and in the Scoria of Smelting Furnaces.

Zinc is found in nature :

a. With Sulphur, as in Zinc Blende [Zn S], which is often contaminated with other Sulphides; exempli gratia, Sulphides of Iron, Lead, Cadmium, Silver, et cetera.

b. In an oxidized state, with Earths, or other Metallic Oxides, as with Alumina, Magnesia, and Protoxide of Iron, also Aluminous Oxide of Zinc, in Automalite or Gahnite, which is an Aluminate of Zinc and of Iron. By some mineralogists it is considered as a variety of Spinel, and as it contains twenty-five to

thirty per cent. of the Oxide of Zinc, it has been called Zinciferous Spinel,

=

Zn O

O

[Mg Al O3]; some varieties contain Silicic Acid, and traces of Manganese, Lime, Sulphur, and Cadmium; with a small quantity of Iron and Manganese, in Red Oxide of Zincusually mixed with some Red Oxide of Manganese-and with a large proportion of Iron and Manganese, in Franklinite, or Zinc Oxydé Ferrifère. The formula, according to KOBELL, is Mn O Mn2 [} N 03]. This formula, supposing the Manganese to exist

Fe

Zn

Fe2

in the state of Red Oxide, can be represented as follows:

Fe O (Mn3 04

Zn Of Fe2 8]. According to GRAHAM, Red Oxide of Manganese [Mn3 O1] is a double oxide, being a compound of single equivalents of Protoxide [Mn O] and Sesquioxide of Manganese [Mn2 O3]. It forms the mineral Hausmanite, which differs from Manganite in having Protoxide of Manganese in the place of Water.

c. As an Oxide, with Sulphuric Acid and Water, in Sulphate of Zinc [Zn O, S O3 HO+6 aq];

d. As a Carbonate, in Calamine [Zn O, C O2]; and with Carbonic Acid and Water, in Zinc Bloom [2 (Zn O, 3 H 0) + 3 (2 Zn O, C 02) ]; and,

e. In combination with Silicic Acid and Water, in Silicious Oxide of Zinc [2 (3 Zn O, Si O2) + 3 aq]; Zinc is also found as an accompanying ingredient in many Silver, Lead, and Copper furnace products; as in the Rohstein,—the product of the first smelting of Copper Ores ;-Bleistein,-which is a similar product, obtained in the smelting of cupriferous and other Lead Ores,-Kupferstein,-obtained by smelting wasted Bleistein with the slags deposited in the Rohstein process, or with Quartzose Copper Ores. It contains from twenty-eight to forty per cent. of copper, and is principally composed of the Sulphides of Copper, Lead, Iron, and Silver ;-Tutty, et cetera. Zinc is also met with in Bleiglanz, Voltzite, Rothzinkerz, Kieselzinkerz, and Jeffersonite.

Examination for Zinc.

This examination is very simple; the substance either containing much or little sulphide of zinc, or else this metal in an oxidized state, is treated with a sufficient quantity of carbonate of soda, upon charcoal, in the reducing flame. Metallic zinc volatilizes, but on coming in contact with the air is again oxidized. When a considerable quantity of this metal is present, the zinc flame is produced, and the charcoal becomes coated with flowers of zinc ; but if a small quantity only, the charcoal is covered with an oxide at a short distance from the assay, and no alteration is observed in the flame.

The sublimate, which when hot is yellow, and after refrigeration white, gives, when treated in the oxidating flame with a few drops of cobalt solution, a beautiful characteristic green color, which is properly recognized only on cooling. When the assay contains much lead, or if an operator is examining metallic lead for zinc, he will find, on treating the substance in the reducing flame, that the oxide of zinc sublimate is not deposited so far from the assay as the lead one, but it may often occur that the lead sublimate is mixed with zinc. To determine if such has taken place, heat the sublimate with a solution of cobalt in the oxidating flaine; the lead, if any is present, becomes reduced by the glowing charcoal, and volatilizes, while the oxide of zinc remains, and gives the characteristic green tinge. Too strong a blast must not be directed upon the moisture, or else the zinc will separate from the charcoal, and is therefore apt to be blown away. This can be avoided by rubbing the spot upon the charcoal where the sublimate generally rests, with a few drops of a cobalt solution; a single drop of the liquid is sufficient for ascertaining the presence of a very small proportion of zinc. When this metal is present in minute quantities only, a strong flame must be deflected upon the substance, which will then become a pyrophorus, and if the assay contains lead or bismuth, it will volatilize.

§ 4. COBALT-Co-Presence in the Mineral Kingdom, and in the Scoria of Smelting Furnaces.

Cobalt is found in the following states :

a. Metallic, mixed with other metals, as with Arsenic, and sometimes traces of Iron, Copper, and Sulphur, in White Cobalt [Co, 2 As], at times [Co, 3 As]; with Arsenic, Iron, and sometimes a little Manganese, in Tin-White Cobalt [Co As + Fe As]; with Selenium and Selenide of Lead, in Selenide of Lead and Cobalt [Co, 2 Se + 3 (Pb Se) ], et cetera ;

ROSE's analysis of the Selenide of Lead and Cobalt :

b. As a Sulphide, in Cobalt-kies [2 Co, 3 S], often with traces of Sulphide of Iron, and Sulphide of Copper; and with Arsenic and a trace of Iron, in Bright White Cobalt [Co, 2 S + Co, 2 As];

c. As an Oxide, with Manganese and water, in variable proportions, in black, brown, and yellow Earthy Cobalt ;

d. As Oxide, with Sulphuric Acid and Water, in Red Vitriol [3 Co O, S 03 + 8 aq]; WINKELBECH analyzed a compound which gave the following formula,-[Mg O, S 03 + 3 (Co O, S 03) + 28 aq];

e. Also in an oxidized state, with Arsenic Acid and Water, in Cobalt Bloom [3 Co O, As 05 + 6 aq ], and Nickelochre.

This metal also occurs, in a small proportion, in different furnace products; namely, in such as are produced from ores. To these belong, Lead and Cobalt Speiss, the principal constituents of which are Nickel and Arsenic, and perhaps also many Iron, Lead, and Kupfer-steins, which fall with the slags, et cetera.

Examination for Cobalt.

Cobalt is a metal which is oxidized with great facility, and in

this state it imparts to the glasses of borax and microcosmic salt a beautiful blue color, both in the oxidating and reducing flames; but simple and complex combinations cannot be treated in this

manner.

If, in the previously described minerals, selenide of lead and the selenide of lead and cobalt are excepted, this metal can be easily determined, if those which are combined with sulphur and arsenic are first roasted upon charcoal, and their fused assays treated with borax in the oxidating flame. The minerals and products containing neither manganese nor iron, give immediately a beautiful blue glass, which, if a great addition of the substance is present, appears black and opaque. If a large quantity of manganese or iron is present, the glass in the first case will be violet, and then green; but if it is operated upon in the reducing flame, the red color of the manganese and the yellow of the iron disappear, the bead acquires a bottle-green tinge, and then becomes either pure blue from cobalt, or greenish-blue from iron and cobalt. If copper or nickel forms a part of the mineral, the oxides of these metals also dissolve in the borax, and color the flux so intensely that the characteristic cobalt blue is not perceptible. If such a glass be treated sufficiently long in the reducing flame, these oxides are deposited in the metallic state, and the blue cobalt color appears, which, if iron is at the same time present, is mixed with a bottle-green hue.

The selenide of lead and selenides of lead and cobalt, also easily fusible furnace products, in which cobalt forms only a small constituent, are treated alone; but the difficultly fusible furnace products are mixed with two or three times their volume of proof lead, and treated with borax on charcoal in the reducing flame, until the glass partakes of the color imparted to it by the readily oxidizable and non-volatile metals. If the glass be covered with the apex of the reducing flame, so as to allow a free access of atmospheric air, only cobalt, iron, and manganese oxidize, these dissolve in the flux, and a more certain determination is effected. In the treatment of a substance containing cobalt, iron, and manganese, the iron is converted into black oxide, giving a bottlegreen color, and the manganese becomes protoxide, and dissolves