142

OXYCHLORIDE OF CARBON.

by exposing them in the sun to the action of an excess of chlorine. Kolbe also found that a mixture of the vapour of bisulphide of carbon and chlorine, when passed through a porcelain tube heated to redness, yielded the same compound. It is a colourless liquid, which is insoluble in water, but soluble in alcohol and in ether; an alcoholic solution of potash decomposes it into chloride and carbonate of potassium 6 KHO + EC1, = 4 KCl+K,€Ð ̧ + 3 H ̧Ð. H2Ð. Tetrachloride of carbon becomes a crystalline solid of pearly lustre at -9° F. If passed through red-hot tubes it is decomposed into free chlorine and a mixture of ethylene-chloride and Faraday's sesquichloride of carbon.

2

(388) OXYCHLORIDE OF CARBON: Chlorocarbonic Acid; Phosgene Gas (EOC,, or C,O,Cl,=99); Theoretic Sp. Gr. 3'42; Observed, 3.68; Mol. Vol.-When equal measures of carbonic oxide and chlorine are exposed to the direct rays of the sun, they combine, and become condensed into half their volume. The combination takes place slowly in the diffused light of day; but no action occurs if the two gases are mixed together and kept in a dark room. There are other modes of obtaining this compound indirectly thus it may be prepared by transmitting carbonic oxide gas through heated perchloride of antimony; the action of light is not necessary in this case. This reaction may sometimes be usefully employed as a test for carbonic oxide when mixed in small quantity with other gases, the pungent odour of the oxychloride which is formed being very characteristic. The composition of the gas is the following:

:

Oxychloride of carbon is a colourless, suffocating gas, which is immediately decomposed by water into carbonic anhydride and hydrochloric acid: ЄOCl2+H2O=Є02+2 HCl. A similar decomposition occurs if it be treated with many of the metallic oxides, such as oxide of zinc, whilst a chloride of the metal is formed; ЄOCl2+ZnO = €0,+ZnCl2. If heated with arsenicum or antimony, the chlorine is removed and carbonic oxide is liberated. Oxychloride of carbon does not possess the characters of an acid; but if the gas be mixed with ammonia in the proportion of I volume of phosgene to 4 volumes of ammonia, both gases are condensed, and form a white volatile solid, which is neutral to testpaper, destitute of smell, and soluble in water and in alcohol slightly

EXTRACTION OF BROMINE FROM BITTERN.

143

diluted, but insoluble in ether. This substance consists of a mixture of chloride of ammonium and carbamide (urea; Natanson) :— 4 H2N+ЄOCl2=2 H ̧NC1+ H ̧Ñ‚¤Ð.

§ II. BROMINE: Br=80.*

Atomic Vol. of Vapour

; Theoretic Sp. Gr. of Vapour, 5'528; Observed, 5'54; of Liquid at 32°, 3'187; Melting-pt. 9°5; Boiling-pt. 145°•4•

(389) BROMINE, so named owing to its irritating odour (from ẞpúμoc a stench), was discovered by Balard in the year 1826, in bittern, which is the mother-liquor of sea water after the less soluble salts have been extracted by crystallization. Bromine exists in sea water in minute quantity, varying from one-third of a grain to about one grain in each gallon; the waters of the Dead Sea also contain bromine in even larger quantity than this: it appears to be combined with magnesium, as bromide of magnesium. Many saline springs, such as those of Kreuznach and Kissingen likewise contain bromine in quantity sufficient to render its extraction from them a source of profit. Indeed, few deposits of chloride of sodium exist in which traces of bromine have not been discovered. It has also been found in a silver ore from Mexico, and it is abundant in the mines of Chañarcillo, in South America; in both cases the bromide of silver is mixed with chloride of silver.

Preparation.-In order to obtain bromine, the mother-liquor from the brine, after all the salts separable by crystallization have been removed, is subjected to a current of chlorine, taking care to avoid an excess of this gas, which would occasion inconvenience by forming a compound with the liberated bromine. All the bromides are decomposed readily by chlorine, the attractions of chlorine being more powerful than those of bromine. In the foregoing operation chloride of magnesium is formed, and bromine is set free: MgBr, + Cl2 = MgCl + Br2; the bromine shows itself by giving to the liquid a beautiful and characteristic yellow colour. This yellow liquid when agitated with ether, parts with its bromine, which is dissolved by the ether. If the mixture be allowed to stand in a glass globe closed at the top by a stopper, and furnished with a glass stopcock at the bottom, the ether rises to the surface, where it forms a beauti

The molecular volume of free bromine being regarded as (Br Br) =

144

EXTRACTION AND PROPERTIES OF BROMINE.

ful golden yellow layer. The mother-liquor is drawn off by opening the stopcock, and the ethereal solution is agitated with a solution of hydrate of potash; the yellow colour immediately disappears; bromide and bromate of potassium are formed and dissolved in the water; 3 Br2+6 KHO=KBrÐ ̧+5KBr+3H2O; whilst the ether, after repose, rises again to the surface despoiled of its bromine, and may again be employed in a repetition of the process upon a fresh quantity of bittern. When the solution of potash has, by repeated charges of bromine, been nearly neutralized, the liquid is evaporated to dryness; the saline mass is gently ignited to decompose the bromate, after which it is mixed with peroxide of manganese and distilled in a retort with sulphuric acid: dense red vapours of bromine pass over, which may be collected in a receiver containing water, and kept cool by ice. The decomposition is of the same nature as that attending the liberation of chlorine from sea salt by means of oxide of manganese and sulphuric acid :

2 KBr+Mn→2+2 H2SO1=K2SO4+MnSO4+2 H2O+Br2.

In this operation a small quantity of chlorine passes over with the bromine, since from the manner in which the bromide of potassium is formed, it is always contaminated with a portion of chloride of potassium. The chlorine unites with part of the bromine, forming chloride of bromine, which is partially decomposed and dissolved by the water in the receiver, while the bromine is condensed in red drops. In order to obtain bromine free from chlorine it must be saturated with hydrate of baryta, which produces a mixture of bromide and chloride with bromate of barium: this mixture must be heated to redness in order to convert the bromate into bromide of barium, and the residue digested in alcohol, which dissolves nothing but the bromide. The bromide of barium is obtained by evaporation of its alcoholic solution, and when heated with black oxide of manganese and sulphuric acid it yields pure bromine.

Properties.-Bromine forms a red liquid, so deep in colour as to be nearly opaque. It has a sp. gr. of 2'966 at 60°: it is very volatile, and emits dense red vapours resembling peroxide of nitrogen in colour (vol. i. fig. 80). In smell it resembles chlorine, and is extremely irritating to the nose and fauces when respired, even if largely diluted with air. When swallowed it operates as a powerfully irritating poison; it acts rapidly on all the organic tissues, and renders the skin permanently yellow. Bromine boils at 145°4 F. (Pierre), and when exposed to a temperature of 9°5 it

BROMINE-HYDROBROMIC ACID.

145

forms a red crystalline solid. The properties of bromine greatly resemble those of chlorine, though they are less strongly developed. It bleaches many vegetable colours. Its vapour will not support the flame of a burning taper. Bromine is slightly soluble in water, and gives to it a yellow colour; it also forms with it a hydrate (Br, 5 H2O; Löwig), which crystallizes in octohedra at 32°. This aqueous solution of bromine is decomposed by sunlight into hydrobromic acid and oxygen. Alcohol dissolves bromine freely, and ether does so still more abundantly. Olefiant gas is rapidly absorbed by liquid bromine, and a liquid compound (Є,H,Br.), bibromide of ethylene, is formed. Bromine combines directly with phosphorus, and with many of the metals, forming compounds termed bromides (540), the act of combination being often attended with ignition, as in the case of antimony and of tin; even gold combines with it, though but slowly; its compound with silver furnishes a material of considerable value in photographic operations.

(390) HYDROBROMIC ACID (HBr=81); Theoretic Sp. Gr. 27986; Observed, 2731; Mol. Vol. -Bromine resembles chlorine in its power of combining with hydrogen, and forming with it a very powerful acid, which is a gaseous body consisting of equal measures of hydrogen and bromine vapour united without change of bulk. The mixture of bromine vapour and hydrogen cannot be detonated by the approach of flame, or by the electric spark, but the two elements may be made to unite slowly, by suspending a red-hot platinum wire in the mixture. If moisture be present the occurrence of combination instantly shows itself by the formation of white fumes, which arise from the union of the newly produced gaseous acid with the aqueous vapour.

Preparation.-1. Hydrobromic acid gas may be procured abundantly by decomposing bromide of potassium with a concentrated solution of phosphoric acid. If sulphuric acid be used for the purpose, the product is impure, since this acid itself undergoes partial deoxidation.

2.-It may also be obtained by decomposing bromide of phosphorus by means of a small quantity of water, when the following reaction occurs :—

phosphorous and hydrobromic acids being produced. This experiment may be easily performed with the aid of a tube bent as in fig. 299. In the bend p, a few fragments of phosphorus and moistened glass are placed, bromine is poured into b, and the

146

HYDROBROMIC ACID-BROMIDES.

tube is closed by a cork, c; on applying a gentle heat at b, the

FIG. 299.

bromine is distilled over and comes into contact with the phosphorus ; the bromide of phosphorus is decomposed by the water at the moment of its formation, and hydrobromic acid escapes by the bent tube, t.

Hydrobromic acid gas is colourless, it is not inflammable, it extinguishes flame, and possesses the usual irritating action of acid gases on the lungs. Faraday succeeded in liquefying the gas under strong pressure; and in a bath of solid carbonic anhydride and ether, he even obtained it in the form of a solid, which melted at -124°. The acid has the following composition :—

Hydrobromic acid gas is very soluble in water, forming, when concentrated, a fuming solution of greater density than hydrochloric acid. A solution of the acid of sp. gr. 1°486 (HBr, 5 H2O) contains about 47 per cent. of the anhydrous acid; it boils at 259°, and may be distilled without change. (See note, p. 151.) Chlorine decomposes it immediately; bromine being set free and hydrochloric acid produced.

The action of hydrobromic acid upon the metallic oxides is analogous to that of hydrochloric acid upon them; bromide of the metal and water being produced; thus hydrobromic acid and hydrate of potash form bromide of potassium and water; KHO + HBr yielding KBr+H2O.

pro

(391) Bromides.-The bromides are all solid at ordinary temperatures: most of them are fused by a moderate heat, and are partially volatilized; and the bromides of gold and platinum are decomposed. Most of the bromides are readily soluble in water. They are all decomposed by chlorine, and when in solution they may be recognised by the yellow colour of bromine which is duced by the addition of a few drops of chlorine water, taking care to avoid an excess of chlorine. On agitating this yellow solution with ether, the bromine is dissolved by the ether, which on standing separates as a yellow liquid, at the top of the colourless aqueous portion. If the quantity of the bromide is very minute, a small quantity of bisulphide of carbon may be advan