the reducing flame it gives a yellowish glass while hot, but when cold it first takes a red tint, and finally becomes a very fine blueish violet. A large quantity renders the colour so opaque, that it appears black, but does not assume the appearance of an enamel. This colour may be made to disappear in the exterior flame. Its reduction is effected better on charcoal than on the platinum wire; but requires even on charcoal a sustained fire. The addition of tin much facilitates the reduction of oxide of titanium. If the oxide of titanium contain iron, or if iron be added to the glass coloured by oxide of titanium, the violet colour disappears, and the glass becomes red in the reducing flame.

Soda dissolves oxide of titanium with effervescence, forming a transparent and deep yellow glass, which does not sink into the charcoal, and becomes white by cooling. This glass possesses the property of crystallizing the instant its ignition ceases. The oxide of titanium is not reducible on charcoal, even with soda.

With solution of cobalt, oxide of titanium takes a black or greyish-black colour.

Oxide of Uranium.-Alone, blackens, but does not fuse.

With borax it fuses into a deep yellow glass, which becomes dull green in the reducing flame. The colour can be restored by exposing it to the oxidating flame on the platinum wire. On charcoal, the same operation is very difficult.

With microcosmic salt it gives a transparent yellow glass on the platinum wire, the colour of which is lessened on cooling, and finally becomes straw-yellow

with a tint of green. In the reducing flame it gives a fine green glass, which becomes yet more beautiful on cooling.

Soda does not dissolve it. With an extremely small quantity of the flux, some signs of fusion may be perceived. The mass, with a larger quantity, becomes a deep brown.

Oxides of Cerium.-Alone, the peroxide becomes protoxide, which latter does not change.

Borax dissolves the oxide in the oxidating flame, giving rise to a fine red or deep orange glass, which becomes lighter, and finally takes a yellow tint, which becomes enamel-white on flaming. In the reducing

flame it loses its colour.

With microcosmic salt the oxide gives by fusion a fine red glass, which on cooling, loses its colour, taking the limpidity of water. In the reducing flame the glass becomes colourless.

With soda it does not fuse; the flux, however, passes into the charcoal.

The reactions of oxide of cerium much resemble those of iron, especially when the cerium is combined with silica. The oxides of iron and cerium do not behave in the same manner with the fluxes, excepting when they are combined with silica, as before stated, in which case it is impossible to detect cerium by means of the blow-pipe.

Oxide of Manganese.-Alone, is not fusible, but becomes brown in a strong flame.

With borax it forms a transparent glass, having the colour of amethyst, which becomes colourless in the

reducing flame. If much oxide be present, the glass must be poured on a cold body, at the instant the blast The colour returns by a slow cooling.

ceases.

With microcosmic salt it fuses readily, forming a transparent glass, which is colourless in the reducing flame, and amethystine in the oxidating flame. If the glass produced by the union of oxide of manganese with phosphoric acid contain so little of the former as to give no sensible re-action, it can be rendered evident by plunging into the bead a crystal of nitre. The bead swells and foams, and the froth becomes on cooling an amethystine or pale rose tint, according to the quantity present.

With soda, the oxide fuses on platinum foil or wire, forming a transparent green glass, which becomes on cooling a blueish green. This assay is best made on platinum foil. One-thousandth of oxide of manganese gives a very perceptible colour with soda.

Oxide of Zinc.-Alone, becomes deep yellow when heated. This assay must be made by day-light. It re-assumes its white colour on cooling. It does not fuse, but gives off a vivid light during incandescence. It is gradually evaporated in the reducing flame, during the continuance of which a white ring is deposited on the charcoal.

With borax it fuses readily, and gives a transparent glass, which becomes milky by flaming, with a large proportion of oxide. It assumes an enamel-white appearance on cooling. In the reducing flame the metal sublimes, and covers the charcoal with a white film.

With microcosmic salt it behaves as with borax, except that the metal sublimes less readily with the first than the second.

Soda does not dissolve it; but acted on by this re-agent on charcoal, it is reduced, and covers the charcoal with a coating of oxide.

With solution of Cobalt it assumes colour.

a fine green

Oxide of Cadmium.—Alone, in the oxidating flame, on platinum foil, undergoes no change. On charcoal it is very soon dissipated, at the same time covering the charcoal with a red or orange-yellow powder. This phenomenon is so decided in oxide of cadmium, that minerals, as carbonate of zinc, for instance, containing only two per cent. of carbonate of cadmium, on being exposed for a moment to the reducing flame, deposit, at a slight distance from the assay, a yellow or orange-yellow ring of oxide of cadmium. The cooler the charcoal is, the better it is observed. This ring forms before that of zinc, and the insufflation must not be long continued, otherwise the coloured ring will be covered by the deposit of oxide of zinc, and the operator be inclined to believe that the mineral contained no cadmium.

Borax dissolves a very large quantity on the platinum wire, forming a transparent glass, whose yellowish colour disappears on cooling. If the glass be nearly saturated, it becomes opaque by flaming, and if quite saturated, it is enamel-white on cooling. On charcoal, the cadmium is reduced, covering the former with its characteristic yellow film.

Microcosmic salt also dissolves a very large quantity,

forming a transparent glass, which, when saturated, forms a milk-white enamel on cooling.

Soda does not fuse it on the platinum wire. It is reduced on charcoal, with the production of the orangeyellow coating.

Oxide of Iron.-Alone, undergoes no change in the oxidating flame; but in the reducing flame, it blackens and becomes magnetic.

With borax it gives a dull red glass in the oxidating flame, which brightens on cooling, and finally takes a yellowish tint, or even becomes colourless on cooling. If the bead contain a very large proportion of oxide, it is opaque in the liquid state, and on cooling, becomes a dull impure yellow. In the reducing flame, it becomes bottle-green; and if the reduction be forced to the highest possible extent, assumes a lively blueish-green tint, exactly like protosulphate of iron. Tin very much accelerates the reduction of the peroxide to the state of protoxide.

With microcosmic salt it behaves as with borax, but the green colour disappears more completely, and may be entirely got rid of by the application of tin.

Soda does not dissolve oxide of iron, but causes it to be absorbed by the charcoal, in which it is easily reduced, and may be obtained as a grey, magnetic, metallic powder.

Oxide of Cobalt.-Alone, suffers no change.

With borax it readily fuses, forming a fine transparent blue glass, which does not become opaque by flaming. A very small quantity colours the glass completely blue; and a large quantity imparts so deep a colour, as to make it appear black.