5. CHLORIDE OF MAGNESIUM. Mg Cl. Uses. The same as those of sulphate of magnesia.

6. SULPHATE OF IRON. Fe 0, SO3.

Uses. For indicating the presence of nitric acid; for this purpose a clean crystal is dropped into the solution under examination, and a little dilute sulphuric acid added; if nitric acid is present, the crystal immediately becomes coated with a brown areola. This reagent is also employed in solution for detecting hydroferricyanic acid, with which it gives a blue precipitate of ferricyanide of iron; when mixed with perchloride of iron and potassa as a test for hydrocyanic acid. If the precipitate thus produced dissolves with a fine blue color in hydrochloric acid, the acid in question is present. Sulphate of iron is likewise employed for reducing the salts of gold.

Uses. It is specially applied as a test for chromic acid and soluble chromates, producing a lemon-yellow precipitate of chromate of lead. When a piece of bibulous paper saturated with this reagent is held for a short time over a solution containing sulphide of hydrogen, it becomes of a dark-brown color, and is of great use for this purpose. Acetate of lead likewise produces precipitates with some other acids, but the principal ones are here given.

8. SULPHATE OF COPPER. Cu O, S 03.

Uses. As a test for arsenious acid, producing a precipitate of yellowish-green arsenite of copper; for arsenic acid, with which it gives a greenish-blue precipitate; when associated with caustic potassa, for distinguishing the former from the latter, arsenious acid and arsenites giving a red precipitate of suboxide of copper; when united with sulphate of iron, for detecting hydriodic acid, throwing down white subiodide of copper, Cu2 I; and, also, for indicating the presence of hydroferrocyanic acid, with which it gives a dark purple-red precipitate of ferrocyanide of copper, Cu2 Cfy.

9. SUBNITRATE OF MERCURY. Hg O, N 05. Uses. This reagent acts anologous with, and, in many cases may be substituted for, nitrate of silver. It is employed as a test for many acids, especially the hydracids; and also for the detection of substances easily capable of oxidation, as formic acid, which deoxidizes it, being converted into carbonic acid and water, with reduction and precipitation of metallic mercury.

10. OXIDE OF MERCURY. Hg O.

Uses. As a test for hydrocyanic acid, dissolving only in alkaline liquids when that acid is present.

11. CHLORIDE OF MERCURY. Hg Cl.

Uses. As a test for hydriodic acid, with which it produces a beautiful red precipitate of iodide of mercury, Hg I. On addition of this reagent to formic acid, it at first falls down as chloride of mercury, but is soon reduced to the metallic state. It serves as an oxidizing agent for chloride of tin, and other substances.

12. SULPHUROUS ACID. SO2.

Uses. As a very powerful reducing agent. It precipitates metallic mercury from solutions of mercurial salts; reduces chromic acid to oxide of chromium, and is employed for the conversion of arsenic into arsenious acid. For these, and many similar purposes, it may either be used in a state of solution, or may be generated when wanted for use by adding sulphuric acid to strips of metallic copper in a flask, and applying heat.

13. CHLORINE. Cl.

Uses.-In solution, for isolating iodine and bromine. It is also employed to decompose many organic substances; it effects this sometimes by withdrawing the hydrogen, forming with it hydrochloric acid, whilst the liberated oxygen enters into a simpler but more permanent combination with the other constituents. The chlorine is best obtained by heating one part of coarsely powdered binoxide of manganese with four or five parts of common hydrochloric acid.

E

14. SULPHINDIGOTIC ACID,

Is a solution of one part of indigo in seven parts of concentrated sulphuric acid.

Uses. As a test for nitric acid, which destroys its color. When the nitric acid is not in a free state, it must be liberated by adding sulphuric acid to the compound.

15. STARCH PASTE,

Is made by triturating starch with water till perfectly mixed. It should have the consistency of cream.

Uses. When paper moistened with starch-paste is exposed to the vapors of iodine-liberated by chlorine or strong sulphuric acid-it is immediately tinged violet. When bromides are treated in a similar manner, the paste assumes an orange-yellow hue.

REAGENTS IN THE DRY WAY.

FLUXES AND BLOWPIPE REAGENTS.

The three principal reagents, indispensable in examinations with the Blowpipe, are—

Carbonate of Soda;

Biborate of Soda, or Borax;

Phosphate of Soda and Ammonia, or

Microcosmic Salt.

These salts especially are to be provided in a state of purity, and will therefore be described separately.

1. CARBONATE OF SODA. Na O, CO2.

When a current of carbonic acid gas is passed through a saturated solution of carbonate of soda in water, bicarbonate of soda is precipitated in crystalline grains, which must be well affused with cold water, and dried. In this state it may be employed for qualitative, but when required in quantitative analysis, it must be calcined in a flat porcelain basin, to liberate the second atom of carbonic acid, and its water of crystallization.

WINKLER obtains the bicarbonate of soda free from sulphate of soda, in the following manner :-He dissolves 4 ounces of crystallized carbonate of soda in 8 ounces of distilled water, and adds to the solution 14 ounce of carbonate of ammonia; then heats the mixture to 132.8° Fahr. on a water-bath. After some time, a large quantity of bicarbonate of soda precipitates, which is separated from the supernatant liquor by filtration.

To ascertain whether the carbonate of soda contains any sulphate, mix two parts with one of pure silica, and fuse this mass upon charcoal, in the reduction flame; if the smallest quantity of sulphate of soda be present, the resulting bead will be of a deep yellow or red color, owing to the formation of sulphide of sodium.

A second method is, to heat a small quantity of carbonate of soda upon charcoal, in the reduction flame, until it is entirely absorbed. Cut out, with a small knife, this part of the charcoal, and digest it in water; to the solution, add a small piece of bright metallic silver; if sulphuric acid had been present, the surface of the silver would become first yellow, then brown, and finally black.

The carbonate of soda, in qualitative examinations with the Blowpipe, determines-first, whether a body fuses or is rendered soluble; second, the presence of silicic acid in combination.

In quantitative analysis, it serves as the means of rendering soluble, silicic acid, tungstic acid, and titanic acid combinations; and also for accelerating the reduction of different metallic oxides. The best method of preparing a large quantity of bicarbonate of soda is to pass a stream of carbonic acid gas over an atomic mixture of crystals of soda and the dry carbonate. Great heat is evolved during the process, owing to the rapidity with which the gas is absorbed.

2. BIBORATE OF SODA. Na O, 2 B 03.

This salt, which is met with in commerce in large masses, must be re-crystallized, to free it from foreign matters. If the crystals yielded are pure, they will give a transparent glass when heated upon the ring of a platinum wire. In quantitative analysis, owing to the crystals occupying so much space when heated, on

account of their intumescence, the borax must be employed in a calcined state. According to BERZELIUS, almost all substances dissolve when fused with borax, and form, with its ingredients, acid and basic combinations; for this reason it is such a valuable flux in Blowpipe experiments.

3. PHOSPHATE OF SODA AND AMMONIA. Na O, NH O, HO, POS.

It is best obtained by heating together, in distilled water, 100 parts of crystallized phosphate of soda, with 16 parts of chloride of ammonium. Chloride of sodium separates, and the liquid, when filtered and evaporated, affords the salt in fine crystals. When this salt is heated upon charcoal, or platinum wire, it loses its water and ammonia, and is converted into metaphosphate of soda, which, in consequence of its excess of acid, has the power of fusing almost every chemical compound.

This salt, in the liquid state, detects magnesia and the protoxide of manganese.

Besides the three reagents described, there are many others necessary to facilitate the fusion, or to effect the decomposition, of certain substances heated before the Blowpipe, and also to aid in the detection of particular elements; these are:

4. NITRATE OF POTASSA. KO, N 05.

This salt is obtained in small prisms, when the saltpetre of commerce is dissolved in hot water, and the liquid allowed to cool gradually.

a. The production of colors, in beads formed with borax or microcosmic salt upon the platinum wire, can sometimes be facilitated by the addition of saltpetre. A small crystal of this salt is supported near the lamp, upon a porcelain capsule, and when the bead is removed from the flame, it is instantly pressed upon the saltpetre. The globule immediately tumefies, and the oxidized metal exhibits its color on the exterior. If the Blowpipeflame is at all altered during this examination, the reaction will be destroyed. By this expedient, a portion of manganese, so minute as otherwise to pass unnoticed, can be readily discerned, by a beautiful emerald green color being produced.