872 



COBALT 



The varieties I. and II. occur in considerable quantities at Schneeberg, in Saxony, 

 associated with silver, copper, and other pyritic ores, quartz and hornstono replacing 

 sulphate of baryta, fluor, and spathic carbonates ; also at Eiecholsdorf, in Hesse ; in 

 Bohemia, Sweden, and in a few localities in the United States. They have also been 

 found in Cornwall ; among other places, at Wheal Sparnon, and Saint Austell 

 Consols. The nearest natural mineral in approach to type No. I. contains about 

 23 per cent, of cobalt ; as a rule, however, the nickeliferous varieties are the more 

 common. The predominance of one or other metal may be determined by exposing 

 the specimens to damp air, when a green crust of arsenate of nickel forms on the 

 varieties in which nickel is most abundant, while a pink incrustation is produced on 

 those richest in cobalt. Type No. III. is the mineral known as arsenical pyrites, 

 which, in reality, often contains a little cobalt, and is treated as a cobalt ore. 



2. Cobaltine, Grey Cobalt, Bright Wldte Cobalt, or Cobalt Glance (CoS l + CoAs) 

 (CoS- + CoA 2 ) differs from Speiss cobalt chiefly by having part of the arsenic 

 replaced by sulphur. It crystallises in the cubical system in forms similar to those 

 of iron pyrites, is of a white colour, with a slightly bronze-red tinge, and a brilliant 

 metallic lustre. Its hardness is less than that of felspar, and specific gravity about 6. 

 The typical composition is : cobalt, 35'5 per cent. ; arsenic, 45'2 per cent. ; sulphur, 

 19 4 3 per cent. The purest natural varieties contain about 33 per cent, of cobalt; 

 these occur in Sweden. At Siegen, in Ehenish Prussia, a variety is found containing 

 only 8 or 9 per cent, of iron, forming three quarters of the whole amount of bases 

 present. Unlike the preceding species, it does not contain nickel. 



3. Linnaite or Cobalt Pyrites. This, although crystallising in the cubical 

 system, is analogous in composition to copper pyrites, being represented by the for- 

 mula CoS + Co 2 S 3 (CoS + Co 2 S s ), with 58 per cent, cobalt and 42 per cent, sulphur : 

 part of the base in either term may be replaced by copper, nickel, or iron. It is the 

 richest of all cobalt ores, some varieties containing as much as 53 per cent, of that 

 substance. It is, however, rare, being found to a small extent only in the Siegen 

 district, and in Sweden. 



Among-the products of the alteration of the above, minerals, are 4. Cobalt Bloom, 

 of the composition SCoO.AsO 5 + 8HO (Co"As 2 O 8 + 8H 2 O) with 37i per cent, of oxide 

 of cobalt : and 5. Earthy Cobalt Ore, a variety of the substance known as Wad or 

 Bog Manganese, which at times contains as much as 15 or 20 per cent, of the same 

 oxide, together with the oxides of iron, manganese, and copper. 6. Cobaltic Bismuth 

 Ore, is a finely crystalline mixture of Speiss cobalt and bismuth-glance, found occa- 

 sionally in the Schneeberg district, containing 10 per cent cobalt and 4 per cent, 

 bismuth. The ores of cobalt, as they come into the hands of the smelter, are, as 

 a rule, so much mixed up with those of nickel, that they are worked for both metals. 



See NICKEL. 



The use of cobalt in the arts is 

 mainly confined to the production 

 of glasses coloured blue by oxide 

 of cobalt, which, when finely pul- 

 verised and levigated, are used 

 as pigments under the name of 

 smalts. Oxide of cobalt, in a pure 

 state, is also prepared, to a certain 

 extent, for the use of porcelain 

 manufacturers. The first point to 

 be considered, therefore, is the 

 production of the oxide, and next 

 the fusion with a sufficient quan- 

 tity of siliceous matter. Earthy 

 cobalt ore may be used in the 

 fusion process, without any further 

 preparation; but those that con- 

 tain sulphur aud arsenic must be 

 subjected to a preliminary calci- 

 nation. Fig. 484 is a horizontal, 

 and fig. 485 a vertical section of 

 the roasting furnace employed for 

 this purpose in the Saxon smalt 

 works. The fire-grate is placed 

 on one side of the hearth, which 

 is of irregular form, being about six feet in breadth at the further end of the furnace, 

 diminishing to 27 inches at the working door. Wood is the fuel employed. The 

 arsenical vapours givpn off during roasting, pass out through the openings, a, a, by a 



484 



485 



