Cobalt, one of the elementary metals. The word cobalt was formerly used to designate a whole group of worthless metals. The superstitious miners imagined that the genii of the mountains resisted all attempts to penetrate their mysteries, and threw all sorts of false ores and unripe metal in the way of the workmen, in order to discourage them from their undertaking. These mountain gnomes or sprites were called kobolds, and the miners gave their name to the worthless ore. The bright shining mineral that vexed the workmen so much was at one time supposed to contain bismuth, and was very little used. These are the first recorded notions, but there is little doubt that cobalt ores were used for coloring glass some thousands of years before in Nineveh, Thebes, and Pompeii, as specimens found in those places resemble the beads and ornaments of modern times. The first, really authentic discovery of cobalt appears to have been made in 1733, by the Swedish chemist Brandt, who called it "cobalt king." Chemical analysis had not at that time attained sufficient progress to enable any one to separate the constituents of ores with absolute certainty, and it was not till 1780 that the existence of cobalt was confirmed by Bergman. Cobalt is one of the metals found in the atmosphere of the sun and in meteorites.
It usually occurs associated with nickel, arsenic, and sulphur, and is frequently an incidental product in the working of copper, bismuth, and nickel ores. The best known minerals are smaltine, called also speiss cobalt, cobaline, glance cobalt, cobalt bloom, and earthy cobalt. The fact that some of the minerals contain arsenic has led to the application of the name cobalt to the black arsenic sold as a fly powder. - Metallic cobalt may be prepared from the oxide by heating two parts of the pure oxide of cobalt and one part of pure cream of tartar for six hours in a covered crucible lined with charcoal, and at a temperature sufficient to melt steel. The regulus obtained in this way is exceedingly hard and brittle, has the color of bismuth, is magnetic, and has a specific gravity of 8.43. By remelting in a clay crucible, it can be freed from carbon, and it then has a silver-white color and a specific gravity of 8.754, is softer than steel, very elastic, does not oxidize in air nor after several days' immersion in water, and is as magnetic as iron. Becquerel found that by electrolysis a brilliant white metal goes to the negative electrode when the chloride of cobalt is first neutralized with ammonia. Prepared in this way, it is quite pure, and is malleable and magnetic.
By treating an aqueous solution of the chloride of cobalt with sodium amalgam, an amalgam of cobalt is formed, from which the mercury can be expelled, and the cobalt obtained in the condition of a fine powder; it can afterward be fused to a pure regulus. The metal resembles steel with a slight red tinge, is very hard, and is said by Deville to be more tena-cious than iron. This latter property may hereafter give a value to wires made of cobalt, where it is required to attain great strength in a small compass. Arsenic and manganese render it brittle. Like pure iron, it requires a very high heat to melt it, and the temperature of fusion appears to be between that of iron and gold. Its specific heat is 0.1096, and its density ranges between 8.513 and 8.7. At a high temperature it burns with a red flame, yielding an oxide. Acids generally dissolve cobalt, nitric acid being especially adapted to this purpose. The metal decomposes water at a red heat, but not at ordinary temperatures. Plunged into fuming nitric acid, it is converted into the passive state, the same as iron, and the duration of this passive state is augmented by previously heating the metal. Antimony and cobalt fused together evolve heat and light, and afford an iron-gray alloy.
The alloy of cobalt and iron is exceedingly hard. Gold and cobalt yield a yellow and very fragile alloy. The alloy of platinum and cobalt is fusible. Cobalt amalgam is white, like silver, which is rendered brittle by it. Alloys of lead and cobalt and tin and cobalt have been made, but possess little interest. Many chemists suppose nickel to be an alloy of cobalt and some other metal. Fairbairn found that the tenacity of cast iron was greatly reduced by its admixture with nickel, and the same result is probable in the case of cobalt. The Litter metal is said to reduce copper from solutions. Weiske found that cobalt was contained in nearly every brand of commercial iron examined, sometimes to the extent of 7 grammes in 100 pounds. Finely divided metallic cobalt is soluble in a boiling solution of caustic potash, and yields a blue liquid, which is supposed to contain cobaltic acid. The finely divided cobalt for this purpose is prepared by heating an intimate mixture of pure oxide with 10 to 12 per cent, of starch meal, or by reducing the oxide with hydrogen.
Cobalt contaminated with phosphorus has a different color from ordinary metal, and loses its lustre in the air. - The oxides and salts of cobalt are distinguished for their beautiful colors, red, blue, yellow, and green; hence they were early used as pigments. If a little oxide of cobalt be added to melted glass, we obtain a mass which after cooling is intensely blue. "When this is ground to powder, it yields the well known smalt, which at one time was extensively employed by paper makers and in the laundry. The color is very fast, as it is not affected by the atmosphere, or by acids or other liquids; and this fact afforded a method of detecting adulterations, as sand or pulverized glass which was simply immersed in some coloring liquid could easily be washed clean by acid. Since the extensive and cheap manufacture of artificial ultramarine was established, the demand for smalt has greatly diminished. There is another blue color formed by the union of alumina and the oxide of cobalt, known as Thenard's blue, which has long been applied in the arts, but, in consequence of its high price, cannot compete with ultramarine.
It can be prepared by mixing 3 parts freshly precipitated moist phosphate or arsenate of cobalt with 12 to 15 parts, also freshly precipitated, of hydrate of alumina, and exposing after drying to a red heat. Thus produced, it is a compact insoluble mass, which can be ground to a fine blue powder. Rinmann's green is a compound of the oxides of zinc and cobalt. It is a much prized green pigment. A beautiful yellow color is produced by mixing the nitrate of potassium with a solution of cobalt; a double nitrate of cobalt and potash is produced, in the form of an insoluble yellow crystalline body, which is not only of value as a color, but offers a remarkably delicate test for the presence of cobalt in solutions. This yellow has been used sparingly, on account of its cost, in aquarelle and oil painting. By precipitating cobalt with phosphate of soda, we have a red-violet color, the shade of which varies according to the temperature at which it is prepared. A fine cobalt brown is produced by calcining a mixture of sulphate of cobalt, ammonia, and iron. Some of the salts of cobalt are red when they contain water, and blue when they are anhydrous. This property is made use of in what is called sympathetic ink.
If we write with a dilute solution of chloride of cobalt on paper, and allow the tracings to dry at ordinary temperatures, the letters will be scarcely visible. Upon the application of heat the writing becomes visible, with a blue color, or sometimes green if nickel be present; the color again disappears on the absorption of moisture. A fine green color is produced by precipitating cobalt from its solutions, by means of a mixture of prussic acid and potash; but the cost of production must prevent any extensive application of this color. Since the discovery of photography, the use of cobalt-blue glass has greatly increased. It is an interesting fact in optics that blue glass permits all the chemical rays of light to pass freely through it, while the yellow are intercepted. Pieces of blue glass are used to eliminate the yellow rays when the colors of flames are to be examined for the violet hue of potash, and in other cases of optical research. The oxide of cobalt, prepared by precipitating the chloride with potassa, has been employed in rheumatism; it is emetic in doses of 10 to 20 grains. The salts of cobalt are irritant poisons.
The employment of metallic cobalt in the manufacture of German silver would make that article too expensive for general use; but in small quantities it enters into alloys, in association with nickel, as an incidental component. The deposition of metallic cobalt by the battery can be accomplished the same as is now so extensively done with nickel, and this method is sometimes employed to procure small quantities of the metal. Some of the salts of cobalt are of great value to the chemist in his laboratory, as affording delicate tests for the presence of other bodies. One of the methods for the manufacture of oxygen from bleaching powders is founded upon the somewhat obscure formation and subsequent decomposition of cobaltic acid. A very small quantity of a solution of cobalt suffices to evolve all of the oxygen from a given quantity of chloride of lime. The ammoniacal compounds of cobalt were prepared and fully studied by Genth and Gibbs. The nitrate of cobalt is sometimes employed as a reagent for the blowpipe. The compounds of cobalt are easily recognized by the intense blue color which they communicate to a bead of borax in the oxidating flame.
Zaffre or safflor is a mixture of roasted ore and quartz, used in pottery.