while hot, but becomes chrome-green during refrigeration, then almost colorless, and when perfectly cold it assumes its red color, unaltered. This change of color shows the presence of chromium.

With borax it dissolves with difficulty, even in a powdered state, to a clear, slightly yellowish, green colored glass, which does not become turbidly streaked.

It is dissolved by microcosmic salt with difficulty when in fragments, but fuses readily and perfectly, when it is employed in the state of a powder, to a clear glass, which has a reddish tint while hot, but during the refrigeration it becomes evidently, though slightly, of a chrome-green.

It is not dissolved by soda, but fuses to a vesicular mass without depositing a sublimate on the charcoal. Fused with soda on platinum foil, the presence of traces of manganese may be detected.

Solution of cobalt communicates a blue color to the fine powder.

From this behavior, we may conclude that, as the mineral dissolves with difficulty in borax, without producing a glass streaked with turbid lines; as by solution in microcosmic salt. no skeleton of silicic acid remains behind; as it does not dissolve when treated with soda, no sublimate being at the same time produced; and as the powder receives a blue color from cobalt solution-the mineral under examination is an aluminate, not a silicate, which contains neither oxide of lead nor zinc.

As the aluminates readily admit of decomposition, by fusion with soda and borax on charcoal,-as has been mentioned when speaking of the examination of such combinations for Magnesia, -the alumina and magnesia, and an unimportant constituent, with the silicic acid, may be recognized with certainty in the spinelle from Ceylon, by further treatment of the fused mass.

Y. SILICATES.

The Silicates can be divided into

a. Monobasic; and,

b. Polybasic Silicates.

The former may be readily recognized as silicates before the Blowpipe; and the base, as it consists of one earth or of one metallic oxide, may often be recognized at the same time.

The latter can also be recognized as silicates by their behavior before the Blowpipe; but the bases do not always admit of being so readily recognized.

In cases where the bases do not admit of being ascertained with accuracy during reactions before the Blowpipe, recourse must be had to the moist way, and the compound decomposed either by fusion with bisulphate of potassa in a platinum spoon, or by fusion with soda and borax on charcoal. The first method answers very well with monobasic silicates, silicates of alumina excepted; the second may be employed with more advantage with polybasic silicates.

1. Tabular Spar.

Heated on a bulb tube, it undergoes no change; it yields, however, a little water.

Held in the forceps, it communicates no tinge to the exterior flame, and fuses on the edges only to a semi-clear glass.

It is readily dissolved in large quantities to a clear glass, which does not become streaked with turbid lines.

It is dissolved by microcosmic salt to a clear glass, leaving a silicious skeleton behind. This glass when moderately saturated, becomes, during refrigeration, opalescent.

With an equal weight of soda, the powder fuses to a vesicular glass, which, on the addition of more soda, tumefies and becomes. infusible.

Solution of nitrate of cobalt renders it difficultly fusible, producing a blue color on the fused edges only.

From these results, we may come to the conclusion that Tabular Spar, as it leaves behind a skeleton of silica when treated with microcosmic salt, is a silicate; and that the base, as the mineral readily dissolves in borax, and as solution of cobalt communicates a blue color to it only where it fuses, must be lime.

To prove this fact more fully, it is only necessary to fuse the powdered silicate with bisulphate of potassa, and treat the fused mass in the manner already described under Lime.

2. Soap Stone.

Heated per se in a bulb tube, this mineral yields a little water, gives off an empyreumatic odor, and becomes black.

The mineral, when held in the forceps and heated in the oxidating flame, becomes white, contracts slightly, and fuses on the thinnest edges to a white enamel. It does not tinge the exterior flame.

Borax readily dissolves it to a clear class, which generally possesses a slight ferruginous tinge.

Microcosmic salt decomposes it, leaving a residue of silica. The clear colorless glass, thus produced, crystallizes on cooling.

With a certain quantity of soda, it fuses to a clear glass, which becomes turbid when either too large or too small a portion of the flux is employed.

Cobalt solution communicates to it a reddish color, when it is exposed for a sufficient time in the state of powder to the oxidating flame.

From these reactions it is quite apparent that Soap Stone is a silicate of magnesia.

As this mineral, however, sometimes contains a little alumina, which cannot be detected by the aid of the dry way alone, the finely pulverized soap stone should be fused with bisulphate of potassa, in order to be certain that alumina is present, and the fused mass decomposed in the manner given under the head of Examination for Magnesia.

3. Pyrosmalite.

Heated per se, in a bulb tube, Pyrosmalite undergoes no change, but yields a little water.

In the forceps it fuses on the edges only, to a black metallic shining slag, which becomes red in the reducing flame.

It is dissolved by borax in the oxidating flame, with a slight effervescence, to a clear glass, of an amethystine color. This color disappears in the reducing flame, and the glass, unless saturated, becomes colorless.

If is with difficulty decomposed by microcosmic salt. When treated in the oxidating flame, it affords an amethyst colored glass, which contains a skeleton of silica; it loses the color in the reducing flame.

With a little soda, it fuses to a black glass; if the flux be increased, a difficultly fusible black slag is formed.

Pyrosmalite is therefore a silicate, the base of which is oxide of manganese. But as it dissolves with effervescence in borax, carbonic acid is present, combined with the oxide.

4. Felspar.

Per se, in a bulb tube, it undergoes no change, and when perfectly transparent, yields no water.

In the forceps it is very difficultly fusible, melting only on the edges to a semi-clear vesicular glass. Like soda, it tinges the exterior flame yellow.

It is dissolved to a clear glass by borax, very slowly, and without effervescence.

It is perfectly decomposed by microcosmic salt, only when in the state of powder; a skeleton of silica being left behind. The glass becomes opalescent on cooling.

The powder fuses with soda very slowly, and with effervescence, producing a very difficultly fusible clear glass, perfectly free from

vesicles.

Solution of cobalt communicates a blue color to the fine powder, on the fused edges only.

Felspar is thus a silicate; and as it is very difficultly soluble in borax, coloring the exterior flame yellow, the base must consist principally of alumina, with a little soda; but it cannot be determined, by the Blowpipe alone, whether or not this silicate is combined with small quantities of other silicates.

About 75 milligrammes of the finely powdered mineral should

therefore be melted with soda and borax, on charcoal, to a clear bead, which should be pulverized, the powder treated with hydrochloric acid, and the solution evaporated to dryness; the chloride formed, dissolved in water; the clear solution separated by filtration from the insoluble silicic acid, and the filtrate examined for the different earths, in the manner given under the Examination for Baryta, Lime, and Alumina. In this way it will be found, that the solution contains a large quantity of alumina, with a trace of lime.

The constituents thus found show that the silicate must be a felspar; but whether it contains soda, or potassa with an accidental trace of soda, can be ascertained only by making a separate test for potassa, in the way given at page 103. Potassa-felspar appears to contain a trace of soda, as it generally colors the exterior flame more or less yellow. If a considerable precipitate of chloride of platinum and potassium is formed, in an alcoholic solution of the alkaline portions of the mineral, it is a potassafelspar, which contains only a trace of soda; but if no precipitate is obtained, it is a soda-felspar. A portion of the hydrochloric acid solution, prepared to examine for the earths, may be employed in testing for potassa, so as to avoid a second fusion of the substance with soda. An experiment may also be made in order to ascertain if fluorine is present.

5. Rohslag, from the Freyberg Smelting Works.

Per se, in the forceps, it readily fuses, retaining its black-green color, and tinges the exterior flame slightly yellow, from traces of soda.

It dissolves easily in borax to a clear glass, which is strongly colored by iron.

Microcosmic salt dissolves it to a clear glass, which is likewise tinged yellow, leaving behind a silicious skeleton.

It readily dissolves with soda on charcoal, with effervescence, to a black bead, which deposits no sublimate on the charcoal when