of the semimetals, according to Cronstedt, of a whitish-grey colour, nearly resembling fine hardened steel, and of the specific gravity of 6.000; but according to others, of a bluish grey, or reddish white colour, and of the specific gravity of 7.700. It is as difficult of fusion as copper, or even gold; and when well purified, scarcely yields to iron itself in this respect. When slowly cooled, it crystallizes, forming on its surface small bundles of needles, or needle-formed prisms, laid on one another, and united into bundles; greatly resembling, according to Mongez, a mass of shaken basaltes. In order to succeed in this crystallization, it is sufficient to melt the cobalt in a crucible till it suffers a kind of ebullition; and, after having taken it from the fire, to incline the vessel while the surface of the semifetal is congealing. By this inclination the portion of metal still fused is poured out, and that which adheres to this kind of geode formed by the cooling of the surfaces of the cobalt is found covered with the crystals sought for. When melted with borax it affords a blue glass, which is the most obvious method of distinguishing its ores amongst all others. It cannot be calcined without considerable difficulty; and the calx, though black in appearance, is in reality of a deep blue. This calx melted with borax, or potash and siliceous sand, affords the blue glass called fumé, very much used in enamel painting and tinged of other glasses, being the most fixed of all colours in the fire.
Cobalt, when calcined along with the calx of arsenic in a gentle heat, assumes a red colour. The same is naturally produced by way of efflorescence, and is then called the bloom or flowers of cobalt. When cobalt and arsenic are melted in a strong fire, they burn with a blue flame. It does not mix either with mercury by any means hitherto known, nor will it form any union with bismuth without the addition of some medium. It is easily soluble in spirit of nitre, and the solution either in this or any other acid is of a red colour; and it is observable that the colour of the acid solutions of this semifetal, instead of fading by dilution with water, becomes more vivid. It is precipitated of a pale red colour from its solutions by acid of sugar, which has the greatest attraction for it; though acid of tartar likewise precipitates it.
Cronstedt, in speaking of this semifetal, makes mention of native cobalt; but other mineralogists assure us that it has never been found perfectly pure in the bowels of the earth. What passes for such, is said by Kirwan to be mineralized by arsenic. That called the grey cobalt ore comes nearest to the purity of the native semifetal, but always holds some quantity of arsenic and iron. It is found in Sweden, Saxony, Norway, and England, particularly at Mendip hills in Somersetshire, and in Cornwall, where Dr Lewis says it has lately been dug up in large quantities. Here it is sometimes found in conjunction with bismuth, and sometimes without it, resembling very much in appearance the Saxon ores from Schnuberg in Münsterland, and produces the finest blue colours by proper management. An arsenicated grey cobalt ore has also been found at Chatelaudren in France.
This kind of ore is solid, heavy, and compact, sometimes dull and sometimes of a bright appearance, crystallized frequently in a teffular and sometimes in a dendritical form; being generally hard enough to strike fire with steel, when an arsenical smell is perceived. It grows black in the fire, is soluble with effervescence in the nitrous acid, from which it may be precipitated by the marine, and affords the Sympathetic Ink mentioned under the article Chemistry, n° 822. This and the blue colour communicated by it to glasses are indeed the two characteristics by which the ores of cobalt are distinguished from other arsenical ores.
The most common ore of cobalt is that called the black or vitreous ore, and Kobalt Mulm or Schlacken Kobalt by the Germans. It is found in a loofe powdery form, sometimes resembling lamp-black, sometimes of a grey colour, in which state it is called cobalt ochre; but when in scoriform half vitrified masses, it obtains the name of vitreous or glaify ore. When this kind of ore contains any sulphur or arsenic, they are only mechanically mixed with it. A small portion of copper, however, is sometimes found in it. It is frequently embodied in stones or sands of a black colour; sometimes it is contained in argillaceous earths of a blue or green colour. Talc, chalk, and gypsum, impregnated with it, are called by the same name; and by some spiegel cobalt.
3. Cobalt mineralized by the arsenical acid, is found either loose and pure, or mixed with chalk or gypsum, or indurated and crystallized in tetrahedral crystals. It is also found in a stalactitical form. It melts easily, and then becomes blue. It frequently invets other cobaltic ores; and is found sometimes in stone and sand. From the experiments of Bergman it appears, that the arsenical acid, and not the calx of arsenic, enters into this combination; for cobalt is never red but when united to an acid. Flowers of cobalt, mineralized by arsenic without any silver, and intermixed with galena, have also been discovered in France.
The flowers or efflorescence of cobalt are often found of a red colour, like other earths, spread very thin on the cobalt ores; and is, when of a pale colour, erroneously called flowers of bismuth. A white cobalt earth or ochre is said to have been found, and examined by a celebrated mineralogist, who found it to resemble the cobalt flowers in every respect except the colour; and indeed it is possible that in these flowers the colour might by length of time, or some other accident, have lost their colour. The indurated flowers of cobalt are commonly crystallized in form of deep red semitransparent rays or radiations. It is found at Schnuberg in Saxony.
Cobalt, mineralized by fulphurated iron, is of a colour nearly resembling tin or silver. It is sometimes found in large masses, sometimes in grains crystallized of a dull white colour, and frequently has the appearance of mifpickle. It has no mixture of arsenic. By calcination it becomes black and not red, which distinguishes it from the pyrites; and it contains so little fulphur, that none can be extracted from it. When dissolved in aqua regia the solution is yellow, but becomes green when boiling hot; which alternation, says Kirwan, is peculiar to marine cobalt. A coarse grained kind of this ore, found in Sweden, becomes flimsy in the fire, and sticks to the iron rods employed in stirring it while calcining. The flaggy kind contains a large quantity of iron, and affords a very beautiful colour as well as the former.
Cobalt mineralized by fulphur, arsenic, and iron, has a great resemblance to the harder kinds of grey cobalt ore, formerly mentioned; but it is never hard enough to strike fire with steel, and sometimes may even be scraped with a knife. The most shining kinds of this and the former species are called cobalt glanze.
The great consumption of cobalt is for the permanent blue colour which it communicates to glasses and enamels, either upon metals, porcelains, or earthenwares of any kind. It is the same blue prepared in a very cheap way by the Dutch, chiefly from the coarse glas or blue glas of cobalt, and called azur de Hollande by the French, and which is employed by laundresses. dresses. But although cobalt is applied to few or no other purposes, the quantities consumed in this way afford sufficient profit to those who have cobalt mines in their possession.
Ores of cobalt, as has already been said, are met with in many parts of Europe. The greatest quantities are found near Schnauberg in the district of Münich in Saxony; also at St Andreasberg in the Upper Harz, where large quantities have been met with for upwards of 30 years past. Formerly an iron ore only was found in this place; but about the beginning of the 14th century, on sinking deeper, it was succeeded by a very rich ore of silver; which also being in length of time exhausted, gave place to cobalt ores. Some pieces, however, are still found in these mines, that contain silver and gold.
The general method of preparing cobalt ores in the large way seems confined to Saxony alone; from whence all other parts of the world, even the East Indies, are constantly supplied. It is supposed that the Chinese, and more particularly the Japanese, had formerly mines of excellent cobalt, with which the fine blues of their ancient porcelains were painted; but it appears that these mines are now exhausted, and that the inferior blues of their present wares are painted with the Saxon zaffre imported to them by the Dutch. For the management of the ore in such a manner as to fit it for giving the desired colour, see the article ZAFFRE.
When cobalt is united to bismuth, by means of nickel, the compound is called speiss. This name is also given to a mixture of cobalt, nickel, bismuth, sulphur, and arsenic.
In Germany and Saxony, the word cobalt is applied to the damps, arsenical vapours, and their effects on the miners; which has induced the vulgar to apply it to an evil spirit whom they suppose to dwell in the mines.
Regulus of Cobalt, a kind of semimetal prepared from cobalt, of a whitish colour inclining to red. See ZAFFRE, and CHEMISTRY, no 1294, &c.