(9.) Bromine (Br).—The bromide of magnesium and sodium exists in many salt springs, and it is from these that the bromine of commerce is obtained. The metallic bromides give the same reactions on silver with the microcosmic bead and copper salt as the metallic chlorides. The purplish color which, however, characterizes the chlorides, is more inclined to greenish with the bromides. If the substance be placed in a flask or glass tube, and fused with bisulphate of potassa, over the spirit-lamp, sulphurous gas and bromine will be eliminated. Bromine will be readily detected by its yellow color and its smell. Bromine may be readily detected by passing a current of chlorine through the fluid, after which ether is added and the whole is agitated. The ether rises to the top, carrying with it the bromine in solution; after being withdrawn, this ether is mixed with potassa, by which the bromide and bromate of potassa are formed. The solution is evaporated to dryness, the residue is fused in a platinum vessel, the bromate is decomposed, while the bromide remains; this must be distilled with sulphuric acid and the binoxide of manganese. A red or brown vapor will then appear, indicating the presence of bromine; this vapor will color starch paste—which may be put in the receiver on purpose—of a deep orange color.
If, to a solution containing a bromide, concentrated sulphuric or nitric acid be added, the bromine is liberated and colors the solution yellow or red. The hypochlorites act in the same manner. The bromine salts are coming into use extensively in photography, in consequence of their greater sensitiveness to the action of light than the chlorides alone.
(10.) Iodine (I).—This element occurs in salt-springs, generally combined with sodium; it also exists in rock-salt; it has likewise been found in sea-water, also in a mineral from Mexico, in combination with silver, and in one from Silesia, in combination with zinc. As sea-water contains iodine, we would consequently expect to find it existing in the sea-weeds, and it is generally from the ashes of these that it is obtained in commerce.
When the metallic iodides are fused with the microcosmic salt and copper, as previously indicated, they impart a green color to the flame. This color cannot be mistaken for the color imparted to the flame by copper alone. When the metallic iodides are fused in a glass tube, closed at one end, with the bisulphate of potassa, the vapor of iodine is liberated, and may be recognized by its characteristic color. Those mineral waters containing iodine can be treated the same as for bromine, as previously indicated, while the violet-colored vapor of the iodine can be easily discerned. The nitrate of silver is the best test for iodine, the yellow color of the iodide of silver being not easily mistaken, while its almost insolubility in ammonia will confirm its identity. The chloride of silver, on the contrary, dissolves in ammonia with the greatest facility.
The reactions of iodine are similar to those of bromine with concentrated sulphuric acid and binoxide of manganese, and with nitric acid: The iodine is released and, if the quantity be not too great, colors the liquid brown. If there be a considerable quantity of iodine present, it is precipitated as a dark colored powder. Either of these, when heated, gives out the violet-color of the iodine.
With starch paste free iodine combines, producing a deep blue compound. If, however, the iodine be in very minute quantity, the color, instead of being blue, will be light violet or rose color.
If to a solution of the sulphate of copper, to which a small portion of sulphurous acid has been added, a liquid containing iodine and bromine is poured in, a dirty, white precipitate of the subiodide of copper is produced, and the bromine remains in the solution. The latter may then be tested for the bromine by strong sulphuric acid.
(11.) Fluorine (Fl).—This element exists combined with sodium, calcium, lithium, aluminium, magnesium, yttrium, and cerium. Fluorine also exists in the enamel of the teeth, and in the bones of some animals. This element has a strong affinity for hydrogen, and, therefore, we find it frequently in the form of hydrofluoric acid. Brazil-wood paper is the most delicate test for hydrofluoric acid, which it tinges of a light yellow color. Phosphoric acid likewise colors Brazil paper yellow, but as this acid is not volatile at a heat sufficient to examine hydrofluoric acid, there can be no mistake. If the substance is supposed to contain this acid, it should be placed on a slip of glass, and moistened with hydrochloric acid, when the test paper may be applied, and the characteristic yellow color will indicate the presence of the fluorine.
As hydrofluoric acid acts upon glass, this property may be used for its detection. The substance may be put into a glass tube, and sulphuric acid poured upon it in sufficient quantity to moisten it; a slight heat applied to the tube will develop the acid, which will act upon the glass of the tube. If the acid is retained in the mineral by a feeble affinity, and water be present, a piece of it may be put in the tube and heated, when the acid gas will be eliminated. The test paper will indicate its presence, even before it has time to act upon the glass. If the temperature be too high, fluosilicic acid is generated, and will form a silicious incrustation upon the cool portion of the tube.
If the fluorine is too minute to produce either of the above reactions, then the following process, recommended by Plattner, should be followed: the assay should be mixed with metaphosphate of soda, formed by heating the microcosmic salt to dull redness. The mass must then be placed in an open glass tube, in such a position that there will be an access of hot air from the flame. Thus 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 Brazil paper, applied to the extremity of the tube, will be instantly colored yellow.