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with their hydrogen, forming hydrochloric acid, their carbon being consequently set free as soot: this is well shown by the introduction of paper dipped in turpentine, or of a lighted taper, into a jar of chlorine.

(d) It imparts no colour to starch-paste.

The specific gravity of chlorine gas is 2:44; being thus much heavier than atmospheric air, it may be collected in vessels filled with that fluid, by allowing it to issue from a delivery-tube at the bottom of the jar to be filled ; in virtue of its superior density it immediately occupies the floor of the jar or bottle,and, gradually rising, buoys up the air upon its surface, until it finally expels it wholly.

Chlorine gas is soluble in cold water; its maximum solubility is in water at 8° C., 1 volume of water at that temperature dissolving 3.04 volumes of the gas; at 50° C., 1 volume dissolves only 1.09 volume; and at 100° C., the temperature of boiling water, it dissolves nothing. In collecting chlorine over water, then, the temperature of the latter is an important point.

As a chemical agent, chlorine is among the most powerful with which we are acquainted, its affinity for the basic elements being so great, that many metals when introduced into the gas in the form of leaf or fine powder, burst into flame from the great energy of their chemical combination: the basic element hydrogen also, when mixed with this gas and exposed to the bright light of the sun or of the voltaic arc, explodes from the same cause. By reason of these powerful affinities it is a very dangerous gas to breathe, since the fine structure of the lungs is very liable to injury from exposure to energetic chemical agents.

II. BROMINE=Br. The non-metallic element, or salt-radical bromine, is a reddish-brown liquid, boiling at 63° C., and becoming solid at -22° C.

Bromine is an element of somewhat rare occurrence in nature; it is chiefly found in combination with sodium (Na), magnesium (Mg), and calcium (Ca), in sea-water and some mineral springs, and more rarely as the mineral, bromide of silver (AgBr). The method for its isolation is the same as that adopted in the case of chlorine; hydrobromic acid being at first set free, is imme

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with their hydrogen, forming hydrochloric acid, their carbon being consequently set free as soot: this is well shown by the introduction of paper dipped in turpentine, or of a lighted taper, into a jar of chlorine.

(d) It imparts no colour to starch-paste.

The specific gravity of chlorine gas is 2:44; being thus much heavier than atmospheric air, it may be collected in vessels filled with that fluid, by allowing it to issue from a delivery-tube at the bottom of the jar to be filled ; in virtue of its superior density it immediately occupies the floor of the jar or bottle,and, gradually rising, buoys up the air upon its surface, until it finally expels it wholly.

Chlorine gas is soluble in cold water; its maximum solubility is in water at 8° C., 1 volume of water at that temperature dissolving 3.04 volumes of the gas ; at 50° C., 1 volume dissolves only 1.09 volume; and at 100° C., the temperature of boiling water, it dissolves nothing. In collecting chlorine over water, then, the temperature of the latter is an important point.

As a chemical agent, chlorine is among the most powerful with which we are acquainted, its affinity for the basic elements being so great, that many metals when introduced into the gas in the form of leaf or fine powder, burst into flame from the great energy of their chemical combination: the basic element hydrogen also, when mixed with this gas and exposed to the bright light of the sun or of the voltaic arc, explodes from the same cause. By reason of these powerful affinities it is a very dangerous gas to breathe, since the fine structure of the lungs is very liable to injury from exposure to energetic chemical agents.

II. BROMINE=Br. The non-metallic element, or salt-radical bromine, is a reddish-brown liquid, boiling at 63° C., and becoming solid at -22° C.

Bromine is an element of somewhat rare occurrence in nature ; it is chiefly found in combination with sodïum (Na), magnesium (Mg), and calcium (Ca), in sea-water and some mineral springs, and more rarely as the mineral, bromide of silver (AgBr). The method for its isolation is the same as that adopted in the case of chlorine; hydrobromic acid being at first set free, is imme

diately decomposed by black oxide of manganese, Mn, 0,, which oxidizes its hydrogen, liberating the bromine, which condenses in the liquid form: by this process the student should prepare a small quantity of bromine and observe

(a) Its physical characters, such as its colour, odour, great volatility, and its solubility in water.

(6) Its bleaching power, somewhat inferior to that of chlorine, (y) Its far less powerful action on hydrocarbons.

(8) That, when brought into contact with starch-paste (made by boiling starch in water), it produces a beautiful series of colours, varying from pale yellow to the richest orange, according to the amount of bromine present.

In the liquid state bromine has a density of 2.966, in the gaseous, of 5:39. .

One part of water at 15° C. dissolves •03003 of liquid bromine. The bromine escapes from its aqueous solution on heating, just as chlorine does.

Bromine is a substance which, in its chemical relations, bears a striking resemblance to chlorine, forming compounds with the various metals possessed of chemical and physical properties almost identical with those of the chlorides. What we, for convenience sake, call the power of chemical attraction, is, however, less between the bromine and the basic element than that manifested by chlorine, which latter element consequently, in many circumstances, removes bromine from its combinations, taking its place. Bromine vapour, although not so injurious to the human organism as chlorine, nevertheless, if breathed in any quantity, acts very detrimentally; and the liquid bromine, if left in contact with the skin, produces a wound very difficult to heal.

III. IODINE=I. The non-metallic element, or salt-radical iodine, is a solid at ordinary temperatures, of a metallic grey colour, and somewhat resembling in appearance the substance known as plumbago or black-lead. Iodine crystallizes in rhomboidal plates, and also in rhombic octahedra, which belong to the same system.

Iodine occurs in nature associated with bromine and chlorine, in the waters of the sea and of various mineral springs, being chemically combined with sodium (Na), calcium (Ca), and magnesium (Mg): it is also sometimes met with combined with silver (Ag). Its great source, however, is the ash obtained by burning sea-weeds: these plants extract the very minute quantity of iodine contained in sea-water, and by continually storing it up in their organisms, succeed in accumulating, comparatively speaking, so large a quantity of iodine as to repay the cost of extraction. It is prepared in precisely the same manner as the two former elements, hydriodic acid being in the first place produced and immediately submitted to the action of black oxide of manganese (Mn,02). The student should prepare a small quantity of iodine by acting with sulphuric acid (H, SO2) and Mn, 0, upon some iodide of potassium, and observe

(a) Its physical characters both in the solid and gaseous condition, its colour and odour, the crystallization of the solid iodine from the vapour on cooling, and its solubility in water.

(3) Its bleaching power, far feebler than that of chlorine or bromine.

(y) Its comparatively feeble action on hydrocarbons.

(8) The very fine and characteristic blue colour which is produced when iodine and starch-paste are mixed.

Iodine melts at the temperature of 107° C., and boils at 180°C., but it passes into the gaseous state long before it reaches its boiling-point, appearing as a violet vapour of exquisite colour. Its density in the solid state at 17° C. is 4.948, and in the gaseous condition 8.716.

Iodine is less soluble in water than bromine, one part of water dissolving .007 of its weight of iodine.

This element bears a strong general likeness to the two preceding elements in its chemical characters; it also resembles them in odour, &c. Its chemical affinities are, however, weaker than those of bromine, and it is displaced from its combinations by that element, just as bromine itself is expelled by chlorine.

IV. FLUORINE=F. The non-metallic element, or salt-radical fluorine, has not yet been isolated.

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