SULPHIDES, METALLIC, formerly known as sulphurets, are combinations of sulphur with a metal. Many of them occur native, and form highly valuable ores. They are all solid at ordinary temperatures, and, with the exception of those of potassium, sodium, calcium, strontium, barium, and magnesium, are insoluble in water; they are, moreover, conductors of electricity. Many of them, especially of those that occur native, exhibit very brilliant and characteristic colors. The same metal may have sev eral sulphides, and in general there is a sulphide for each oxide. The sulphides are, however, sometimes the more numerous. Most of these compounds may be fused at a heat a little above redness, and if the air be excluded, the protosulphides (those contain ing one atom of sulphur and one atom of metal) remain unaffected; but many of the higher sulphides, such as the bisulphide of iron (FeS,) and the bisulphide of tin give off an atom of sulphur, and are reduced to protosulphides. If, however, there is a free admission of air or of oxygen gas to the heated sulphides, they are all decomposed, the sulphur becoming oxidized, and passing off as sulphurous acid while the metal usually remains in combination with oxygen. When heated before the blowpipe, most of the sulphides evolve an odor of sulphurous acid, and very small quantities of soluble sulphides may be detected in neutral or alkaline solutions by the addition of a solution of nitroprusside of sodium (Na,,Fe,CyGNO, 4Aq), when a magnificent purple color, which, however, is not permanent, is evolved. It has very recently been discovered by Mr. Barrett, and announced in his paper, "On some Physical Effects produced by the contact of a Hydrogen Flame with various Bodies," in the Philosophical Magazine for Nov., 1865, that the sudden appearance of a blue color when the hydrogen flame is 'brought in contact with a body containing sulphur, is a most delicate test for the pres ence of this element, detecting it even when the nitro-prusside of sodium test fails. By this test Mr. Barrett detectedof a grain of sulphur.
The sulphides, are preparer i':'"Various ways, of which it is sufficient to notice the most important. (1.) The protosulphides of the metals of the alkalies and alkaline earths
may be obtained by decomposing their sulphates by igniting them in closed vessels with charcoal, the oxygen being removed in the form of carbonic oxide. (2.) Many of the metals, when heated with sulphur, combine directly with it; sulphide of iron, for example, is kaually prepared in this manner. (3.) Hydrated sulphide of tin, titanium, molybdenum, tungsten, arsenic, antimony, bismuth, copper, lead, mercury, silver, gold, and platinum with its allied metals may be obtained by passing a stream of sulphuret- ted hydrogen through neutral or acid solutions of their salts, when they are precipitated i in an insoluble form; and the hydrated sulphides of zinc, iron, manganese, cobalt, and nickel may be prepared by double decomposition, by mixing a solution of the salt of the metal with a solution of a sulphide of one of the metals of the alkalies, as, for exam ple, sulphide of potassium: thus, sulphate of zinc, if mixed with sulphide of potassium, yields sulphate of potash, which remains in solution, and sulphide of manganese, which falls as an insoluble precipitate. " In many cases," says prof. Miller, " the atoms of these hydrated sulphides are characteristic of the metal; for example, the hydrated sul phide of zinc is white; that of manganese, flesh red; those of cadmium, arsenic, and persulphide of tin are yellow; that of tersulphide of antimony is orange red; and that of hydrated protosulphide of tin is chocolate brown. The sulphides of molybdenum, rhodium, iridium, and osmium are brown, each with its peculiar shade, while in a large number of instances—including the sulphides of iron, cobalt, nickel, uranium, vana dium, bismuth, copper, lead, silver, mercury, gold, platinum, and palladium—the pre cipitated sulphides are of a black, more or less Chemistry, 2d ed. 1860, p. 322. A recollection of the colors of these precipitates will save the young chemist a large amount of labor in testing for the presence of the metals.