it has a basic reaction. Drop carefully into the solution some hydrochloric acid, until neither the red nor the blue paper is affected by it. If you put the liquid in a warm place a salt will be deposited in small cubes; you readily perceive, both by the shape of the crystals and by the taste, that it is common salt. Carbonic anhydride escapes with effervescence.

Experiment 8.-To a little water in a test-tube add a drop of hydrochloric acid or a grain of a soluble chloride, such as common salt, and then a few drops of a solution of silver nitrate (lunar caustic); a white cloudiness is formed which does not happen in pure water. This cloudiness or precipitate is due to the formation of silver chloride, which is insoluble in water, but it may be dissolved by adding some solution of ammonia. Nitrate of silver is a most accurate test for hydrochloric acid or for chlorides:

AgNO,+ NaCl = AgCl + NaNO3.

Bromine is a deep brownish-red, heavy, and very volatile liquid. Its name is derived from the Greek word ẞpoμos, signifying a disagreeable odour. Bromine, at common temperatures, emits yellowish-red fumes, which have a penetrating and offensive odour, resembling that of chlorine. It produces a yellow colour with starch, is sparingly soluble in water, but very soluble in ether. Its specific gravity is 3.

Bromine occurs in many mineral waters, some of which, as the Kreutznach spring, are comparatively rich in it, and form the source from whence it is obtained on the Continent. But in this country the chief supply is derived from seawater. A large quantity of common salt is obtained by evaporating sea-water, and it is from the residual liquid, which is technically called bittern, that bromine is obtained. The bittern is mixed in a retort with manganese peroxide, and hydrochloric acid. On the application of heat the chlorine liberated from the acid decomposes the magnesium bromide contained in the bittern, and bromine, mixed with water, distils over:

MgBr,+ Cl2 = MgCl2+ Br2.

The bromine is separated from the water by shaking it with ether. The ethereal solution, which has a brown colour, floats on the water and can be drawn off. The bromine is then extracted by a somewhat complex process.

Experiment 1.-The processes for the preparation of bromine may be imitated by the student by dissolving a few grains of potassium bromide in a little water contained in a long test-tube; this may represent the bittern. A little chlorine water will liberate the bromine, and the solution will become brown. If a drachm or two of ether is then added and the mixture violently shaken for a minute, the ether will remove all the bromine, and on standing a little while will float as a dark layer on the surface of the water. Pour off the dark-coloured ether into a porcelain basin, and add a few drops of potassium hydrate (caustic potash); it will become colourless. Heat it gently until all the liquid is driven off and a white substance will remain behind, which on cooling may be mixed with a few grains of manganese peroxide, and two or three drops of sulphuric acid, and again heated. Free bromine will then be evolved as brown vapours, very readily seen against the white sides of the basin.

Experiment 2.-Pour a few drops of bromine into a small phial with some distilled water, and shake the mixture well. The bromine will partly dissolve and form a brown solution. This may be preserved and labelled “Bromine solution."

Experiment 3.-Add a few drops of the above solution to a little very weak mucilage of starch, made by mixing a few grains of starch with a little cold, and then adding a considerable quantity of boiling, water with continual stirring. A pale yellow colour will be produced, owing to the formation of bromide of starch.

Experiment 4.-To a drop of bromine contained in a wine-glass add a minute fragment of phosphorus, which must be cut off under water, as it is very inflammable, and carefully and quickly dried in a piece of blotting-paper. The best plan is to drop the phosphorus from the point of a knife on to the bromine. The phosphorus will be immediately inflamed, and a smart explosion will occur.

Iodine is a black solid of metallic lustre; it smells somewhat like chlorine, has a pungent taste, and stains the skin brown.

It occurs in small quantity in sea-water, from which it is separated and assimilated by the various sea-weeds, which thus accumulate a considerable quantity; and it is from the ashes of certain kinds of sea-weeds that iodine is always obtained, for sea-water contains much too small a quantity to render its extraction profitable. The sea-weed is burnt and the ash, or kelp, as it is called, contains the iodine in the forms of magnesium iodide, MgI2, and sodium iodide, NaI. The kelp, after some preliminary treatment, is heated with black oxide of manganese and sulphuric acid, and yields iodine just as the chlorides or bromides yield chlorine and bromine respectively when treated in the same way.

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Experiment 1.-To a few grains of potassium iodide, or some other iodide, in a test-tube, add an equal weight of black oxide of manganese, and a drop or two of sulphuric acid, and heat gently. Beautiful violet vapours of iodine will be produced, and will condense on the sides of the test-tube as black, shining spangles. The following change occurs: 2KI+MnO2 + 2H2SO. K2SO4 + MnSO1+ 2H2O+ I2. Experiment 2.-Dissolve a grain or two of potassium iodide in a little distilled water in a test-tube, and add a little solution of silver nitrate. A light yellow precipitate (silver iodide) will be thrown down, which will not be redissolved on the addition of solution of ammonia, thus clearly distinguishing it from the similar white precipitate obtained with chlorides.

Experiment 3.-Put 24 grains of iodine into a flask, and pour over them half an ounce of strong alcohol; if the iodine is pure it will entirely dissolve. This dark brown solution is called tincture of iodine. Water dissolves only a trace of iodine, but yet is rendered yellow by it.

Experiment 4.-Put a little iodine upon a knife, and hold it over the flame of a lamp; the iodine melts, and is afterwards converted into a violet-coloured gas-vapour of iodine.

As the iodine fumes are nearly nine times heavier than common air, they sink in it. Iodine owes its name to the colour of its vapour, the Greek word iúdŋs meaning violetcoloured. The vapour appears more beautiful when the iodine is heated in a small flask. After cooling, the walls of the flask become lined with small brilliant crystals of solid iodine, affording an example that regular crystals may be formed when bodies pass from the aeriform into the solid state.

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Experiment 5.-Boil one grain of starch in a test-tube with one drachm of water, and add to the thin paste thus obtained a few drops of tincture of iodine; the iodine combines with the starch; the combination is of a deep blue colour. blue colour disappears on careful heating, but returns again on cooling. If one drop of the starch paste is mixed with one quart of water, even at this extreme dilution, the iodine tincture will impart to it a violet tinge. Consequently it is an exceedingly delicate test for detecting starch, and starch, on the other hand, for detecting iodine. If a little tincture of iodine is dropped upon flour, bread, potatoes, &c., the presence of starch in these substances will at once be indicated.

COMPOUNDS OF BROMINE AND IODINE WITH HYDROGEN.

Hydrobromic Acid, HBr, and Hydriodic Acid, HI.-Both of these acids closely resemble hydrochloric acid. They are colourless gases, which fume strongly in air, and are readily soluble in water, forming acid solutions. With bases they form iodides and bromides:

Both bromine and iodine are faithful companions of chlorine; wherever common salt occurs, whether in the earth, the sea, or mineral springs, small quantities of them are present, not in a free state, however, but combined with metals. The different sea-weeds attract these combinations from the sea-water, and from these sea-weeds iodine and bromine are extracted. Both have poisonous properties.

FLUORINE.

Symbol, F = 19. Formula unknown.

Fluorine is unknown in its isolated state. When liberated from its compounds it acts energetically on all substances of which vessels are ordinarily made. The mineral known as fluor-spar consists of fluorine and calcium.

Hydrofluoric Acid, HF.

Experiment 1.-Fashion a small basin out of a piece of thin sheet lead, place in it about a quarter of an ounce of powdered fluor-spar, and half an ounce of strong sulphuric acid, and apply a gentle heat. Fumes of hydrofluoric acid will arise, which are extremely irritating to the eyes, and which resemble those of hydrochloric acid. Fluor-spar (calcium fluoride) is decomposed by sulphuric acid just as common salt is:

CaF2+H2SO1 = CaSO, + 2HF.

Hydrofluoric acid is intensely corrosive, and it attacks and destroys glass and earthenware and most other materials. But it does not act upon lead; therefore vessels made of that material must be used to prepare it in. The most interesting property of hydrofluoric acid is its power of corroding glass, and it is often used in the arts to etch designs upon glass, which is done in the following manner.

Experiment 2. Thoroughly warm a small square of window glass, and then rub over one side of it with a piece of wax, so as to make a smooth coating. When the glass has become cold and the wax hard, scratch any design with a pointed instrument on the coated side of the plate, taking care to cut quite through the wax. The glass plate thus prepared is then laid with the waxed side downwards, so as to cover the leaden basin in which the hydrofluoric acid is being prepared as directed in Experiment 1.

If, after being exposed to the acid fumes for a few minutes, the plate is removed and cleaned from the wax with a rag and a little turpentine, it will be found corroded wherever the marks have been made, and the design will remain engraved on the glass.