according to its quantity is precipitated as a black powder, or remains in solution, imparting a brown color to the liquid. On heating this, the characteristic vapors of iodine are obtained.

Free iodine produces with starch-paste, a blue combination; if it is in minute quantity, however, the result may be a violet or rose-red tinge.

Bromine and iodine may be separated by adding to the liquid containing them, a solution of a subsalt of copper-sulphate of copper to which sulphurous acid has been added, serves the purpose; a dingy-white precipitate of subiodide of copper falls down, which may be filtered off, and the filtrate tested for bromine by adding strong sulphuric acid; if the slightest coloration occurs, the presence of this element is indicated.

§ 8. FLUORINE-Fl—Presence in the Mineral Kingdom.

Fluorine is always found in combination. The minerals in which it forms an essential or secondary ingredient have been cited under Soda, Lithia, Lime, Magnesia, Alumina, Yttria, and Cerium. Traces of Fluorine have been found in the teeth, and also in the bones, of different animals.

Examination for Fluorine, or for Hydrofluoric Acid.

Hydrofluoric acid is not so readily eliminated by heat, from substances in which fluorine forms an essential ingredient, exempli gratia, Fluor Spar, Topaz, Cryolite, et cetera,-as from those in which it sometimes occurs as a contingent one, as in Mica and Hornblende, when it is expelled generally as hydrofluosilicic acid.

If a small quantity of hydrofluoric acid be held in feeble combination, in a mineral containing water, it is necessary to heat it in a test tube, and appply a strip of moistened Brazilwood paper to its mouth. As the temperature augments, fluosilicic acid will be evolved, a silicious circle formed at a short distance from the

assay, and the Brazilwood paper tinged straw-yellow, by the hydrofluoric acid.

According to the experiments of BONSDORF, Brazilwood paper is likewise colored straw-yellow by phosphoric and oxalic acids, but not by sulphuric, nitric, arsenic, or boracic acids. As phosphoric acid, however, is not volatile in such an examination, the tinge acquired by the paper will indicate the presence of fluorine. This test is so delicate, that it is only necessary, at times, to moisten the compound fluoride with hydrochloric acid, on a watch glass, and then to apply the reagent paper. When a substance under examination for fluorine produces no etching upon the glass, and affords no reaction with the Brazilwood paper, the following method must be adopted :-Mix the assay with metaphosphate of soda,-formed by heating the microcosmic salt to incipient redness,—and heat the mass in the end of an open glass tube, in such a position that there will be an access of hot air from the flame; by this procedure aqueous hydrofluoric acid is formed, which can be recognized by its smell, being more suffocating than chlorine, and also by the etching produced by the condensation of vapor in the tube. Moist Brazilwood paper, applied to the extremity of the tube, will be instantly colored.

The subjoined is MERLET'S method for the detection of this acid :-Pulverize the substance for examination, then triturate it to an impalpable powder, and mix it with an equal part of bisulphate of potassa. Heat the mass gradually in a moderately wide dry test tube. The judicious application of heat must be strictly observed, for if the operator first heats the part of the tube where the assay rests, the whole may be lost, on account of the glass being shattered. The spirit flame must first be applied to the fore part of the tube, and then made to recede slowly, until it fuses the assay. After the mixture has been for some time kept in a molten state, the lamp must be withdrawn, and the part containing the assay severed with a file. The fore part of the tube must then be well washed, and afterwards dried with bibulous paper. Should the fluorine contained in the substance be significant, the glass tube, when held up to the light, will be

found to have lost its transparency, and to be very rough to the touch. Of all known substances, hydrofluoric acid is the most destructive to animal matter. When a drop of the concentrated acid comes in contact with the skin, instantaneous disorganization ensues, and a deep ulceration of a malignant character is produced. On this account, the greatest care is requisite in its preparation. It acts energetically on glass, the transparency of which is instantly destroyed, heat is evolved, the acid boils, and in a short time entirely disappears. A colorless gas, commonly known by the name of hydrofluosilicic acid gas, is the sole product. This compound is always formed when hydrofluoric acid comes in contact with a silicious substance.

§ 9. CARBON-C-and CARBONIC ACID-C 02-Presence in the Mineral Kingdom.

Carbon occurs in nature in a pure state, as Diamond; and in combination with other bodies, in Anthracite, Graphite, Stone Coal, Brown Coal, et cetera.

Carbonic Acid occurs in minerals combined with bases which have been included in former sections of this work; it is also met with in the gaseous form, in mines and volcanic regions, and places where the earth contains large quantities of carbonate of lime; but as the examination of free gases does not come within the province of the Blowpipe, it is not requisite to enumerate the different places where this gas is exhaled.

Examination for Carbon and Carbonic Acid.

The diamond is so difficult to burn, that the ordinary Blowpipe is not sufficiently powerful. It may be heated to whiteness, in a covered crucible, without injury; but it begins to burn, in the open air, at about the melting point of silver-703.2° C.,-and is entirely converted into carbonic acid gas. It is more quickly consumed in fused nitre, when the carbonic acid is retained by

the potassa: this is a simple mode of analyzing the diamond, by which it has been proved to be perfectly pure carbon. Some varieties of charcoal, when ignited with anhydrous alum in the oxidating flame, leave a recrementitious mass, consisting of ferruginous and earthy particles. When they are pulverized, mixed with nitrate of potassa, and heated strongly in a platinum spoon, they detonate, and afford carbonate of potassa.

The presence of carbonic acid is detected by the gas being eliminated with effervescence on heating a mineral containing it before the Blowpipe. It is also readily detected by moistening the substance with a few drops of hydrochloric acid-effervescence likewise ensues.

§ 10. BORACIC ACID-B 03—Presence in the Mineral Kingdom.

This Acid occurs combined with Water in Native Boracic Acid; also in several minerals in combination with various bases. Those in which it forms an essential or secondary ingredient have been already adverted to, under Soda, Lime, Magnesia, and Alumina.

Examination for Boracic Acid.

According to BERZELIUS, Native Boracic Acid of Tuscany produces the following reactions:-Moistened with water and placed on Brazilwood paper, it bleaches the paper in about half an hour; a solution in alcohol applied to curcuma paper imparts a brown tint.

Per se, on charcoal, it melts to a clear glass; should it contain gypsum, the assay will be opaque when cold.

TURNER has recommended the following method for the detection of boracic acid in salts and minerals. Reduce the substance to an impalpable powder, and mix it with a flux consisting of four and a half parts of bisulphate of potassa, and one part of finely powdered fluor spar. Knead the whole into a paste, with a few drops of water; then place the moist assay on the platinum

ring, and fuse the mass with the apex of the blue flame. During the fusion of the assay, fluoboric acid gas is liberated, which communicates a pure green color to the outer flame. Great care must be taken, when only a small quantity of boracic acid is present, for the coloring will be momentary. MERLET remarks that the reaction will be more certain, when three to four parts of the flux are used with one of the substance.

§ 11. SILICIC ACID—Si O2-Presence in the Mineral Kingdom, and in Furnace Products.

Silicic Acid forms a principal ingredient of the solid parts of our globe. It is found in nearly a pure state, in Berg-Crystal, Quartz, Chalcedony, Hornstone, Cornelian, Flint, et cetera. When any of the preceding minerals are colored, it is generally owing to the presence of Iron or Manganese. The native silicates have been cited under the Earths and Metals. Lastly, it is considered as an essential ingredient of dressed Ores and Slags.

Examination for Silicic Acid.

The Berg-Crystal and Milk-Quartz comport themselves with the fluxes, like pure silicic acid. The other varieties of Quartz, as regards their solubility in the fluxes, behave in the same manner; but the colors imparted to the borax or microcosmic glasses by the metallic oxides are more or less visible, according to the one contained.

The silicates are recognized by means of microcosmic salt and soda. They are decomposed in such a manner by the former, that their bases combine only with the free acid in the flux, and the silicic acid separates. This examination is generally performed on a platinum wire. The microcosmic salt must first be fused into a bead, the silicate added, and the whole treated in the oxidating flame. The glass bead, while hot, is clear, and the separated silica floats through it in a collected state. As glasses are obtained by numerous silicates, which are perfectly clear while