hot, but opaline on cooling, the operator must carefully observe the flux in its molten state, for the presence of silica. The silicious appearance is generally observable with those compounds of silicic acid which have lime, magnesia, glucina, yttria, or oxide of zinc, for the base.

Silicates of Zirconia, as Hyacinth and Zircon, are with great difficulty acted upon by microcosmic salt. The preferable method for the detection of the acid in these minerals has been given under Zirconia. If a substance contains a small quantity only of silicate, or be intermixed with some quartz, a glass is obtained, in which no skeleton of silica appears, owing to the solution of the silicic acid; it can be detected, however, by the aid of the moist way, proceeding in the manner given in the examination of the different Earthy Silicates. The silicic acid is separated in such a condition by this method, that it can afterwards be recognized with a little microcosmic salt on a platinum wire, or with soda on charcoal.

The silicates dissolve imperfectly in soda, on a platinum wire or charcoal, with effervescence. If it be a compound, in which the oxygen of the silicic acid is at least double that of the base, a clear glass will be obtained by the judicious application of soda, which will remain the same when cold, because the glass of silicate of soda acts as a solvent on the free bases.

A silicate containing an infusible base, gives a clear glass with a little soda. With a slight addition of soda, the glass is opaque; and with another supply, the assay becomes intact.

By the first addition of soda, a part of the base separates, which is redissolved, and the glass is clear; but when a large addition of the flux is supplied, so much of the base separates that the whole assay becomes infusible.

Substances in which only a small quantity of a silicate is contained, which is not at all detectible by soda, must be treated in the moist way. This method also must be resorted to in the examination of dressed ores, often containing metallic sulphides and arsenides, for silicic acid.

¶ Examples of the Method of Procedure employed in Examining the different Compounds for all their constituents,

with the aid of the Blowpipe.

a. SALTS.

Salts come under the following heads :

a. Those which have Alkalies, for bases;

b. Those which have Earths;

c. Those which have Earths and Alkalies together;

d. Those which have Metallic Oxides; and

e. Those which have Metallic Oxides and Earths together. These different salts may often be distinguished from each other by their external characters, and thus immediately recognized; cases, however, occur, which cannot be so easily determined, and recourse therefore must be had to chemical analysis.

Such an examination can be easily performed with the Blowpipe, and the whole operation completed in a short time, if the proper method be undertaken; which will be shown in succeeding examples.

1. Sulphate of Potassa-K O, S 03.

If this salt be in the state of powder, it is not possible to determine, from external appearances, whether the base is an earth, an alkali, or a metallic oxide; the examination should therefore be conducted in the following manner:-A small portion of the salt is heated in a bulb tube, and examined in order to see if it yields water; if it be employed in a crystalline state, it decrepitates, but yields none. The pulverized salt is next mixed with soda, this mixture fused on platinum foil in the oxidating flame, and examined during the fusion, in order to see if the whole mass fuses clear, or if any thing is precipitated. Sulphate of potassa fuses with soda on platinum foil to a perfectly clear glass; the base, therefore, is an alkali. The particular alkali is determined by examining how the exterior flame is

colored, when a small fragment adhering to the moistened loop of the platinum wire is fused at the point of the blue flame. If the exterior flame exhibits a violet tinge, the presence of potassa is at

once seen.

If the acid also is to be determined, a small portion must be treated on charcoal in the reducing flame. The salt under examination fuses, and is absorbed by the charcoal, which it coats with a white substance, formed of a number of orbicles, similar to that produced by sulphate of potassa, or a combination of potassium, with chlorine, bromine, or iodine. If the mass absorbed by the charcoal be moistened with a drop of water, it gives off a strong hepatical odor, and when removed from the charcoal and placed on a slip of silver foil, it produces a black spot of sulphide of silver on being moistened with water.

By this simple examination, it is ascertained that the constituents of this salt are sulphuric acid and potassa.

2. Nitrate of Potassa-Saltpetre-K O, N 03,

If the salt cannot be recognized by its external characters, the examination is conducted in the same manner as the preceding.

Heated in a bulb tube, it fuses readily, giving a clear glass, and yields no water. By this test it is already known that the base is an alkali; the test with soda on platinum foil may consequently be omitted.

Kept in a state of fusion on platinum wire, it colors the exterior flame violet. The base is consequently potassa.

Ignited on charcoal, its surface becomes exceedingly vesicular. The acid is therefore nitric acid.

3. Iodide of Potassium-K I.

When a small quantity is heated in a test tube with bisulphate of potassa or sulphuric acid, purple vapors are given off, which communicate a blue color to starch.

4. Carbonate of Soda-Na O, C O2.

In the examination of this salt, the procedure in the commencement is similar; but it must be further treated, because the acid cannot be thus recognized.

The hydrated salt yields water in a bulb tube, which reacts neither acid nor alkaline.

It fuses to a clear glass with soda on charcoal. The base is consequently an alkali.

It fuses readily on platinum wire, and tinges the exterior flame strongly yellow. The base is consequently soda.

It melts on charcoal without detonating, is absorbed by the charcoal, but gives no sublimate. It is consequently not in combination with nitric, sulphuric, or hydrochloric acids.

It reacts alkaline with turmeric, or with reddened litmus paper.

It is now to be determined whether the soda is combined with carbonic acid. For this purpose, a small specimen of the salt should be fused with silicic acid on charcoal, and examined, in order to see if the two substances combine to form a clear glass with effervescence. This is the case with carbonate of soda, because its acid is evolved while the soda combines with the silicic acid. If the glass becomes of a yellow or a red color on cooling, the carbonate of soda is not free from an admixture of sulphuric acid.

5. Chloride of Ammonium-N H✦ Cl.

In testing for water in a bulb tube, if the salt sublimes without leaving a residue, it must be an ammoniacal salt. If it then be tested with soda, for ammonia, and with a microcosmic salt bead saturated with oxide of copper, for chlorine, results are obtained, which can be obtained with chloride of ammonium. only.

6. Sulphate of Soda-Na O, S O3 + 10 aq.

When heated in a test tube it gives off water; the residue is

infusible. On charcoal, the flame is colored of an intense reddishyellow. The residue gives off sulphide of hydrogen on being moistened with an acid.

7. Potassa-Alum-Al2 O3, 3 S 03 + K O, S O3 + 24 aq.

When this salt is pulverized, it cannot be recognized as alum, unless from the taste; nor can we determine, from its external character, whether the base is an alkali or an earth, or whether both act as a base. The operation must, therefore, be conducted in a manner similar to that given for sulphate of potassa.

In a bulb tube, alum fuses, tumefies, and yields water, which reacts neither acid nor alkaline. The dry mass ignited, gives an acid, which reddens moistened litmus paper placed in the upper part of the tube. By the further examination of the salt, this acid is determined.

It forms an infusible compound with soda on platinum foil when its water is driven off. The base, therefore, appears to be an earth. But if a small portion be treated per se on a platinum wire at the point of the blue flame, the exterior flame will be colored deeply violet, from potassa. So far it is thus known that the salt has two bases, of which the earthy one remains to be ascertained.

As the salt appears perfectly white after the removal of its water, it should be tested with solution of cobalt; when it becomes colored of a beautiful blue, if, in separating the water from the substance on charcoal, a pure oxidating flame has been employed. This shows the base to be alumina.

The acid only now remains to be determined. It is first tested for sulphuric acid, because, in testing the salt in the bulb tube, litmus paper was reddened. When fused with soda on charcoal in the reducing flame, the fused mass, when laid on silver and moistened with water, produces a black spot of sulphide of silver. The acid is consequently sulphuric: separate tests for other acids produce no reaction; the salt, therefore, consists of sulphate of alumina and sulphate of potassa.

S