COBALT.

307

For examplej should a house eminent in this line, such as that of Westleys, Friar-street, Doctor-s’-commons, receive 5000 volumes from Messrs. Longman & Co. uponMonday morning, they can have them all ready for publication, within the incrediblyshort period of two days; being far sooner than they could have rudely boarded themupon the former plan. The reduction of price is not the least advantage incident to thehew method, amounting to fully 50 per cent, upon that with leather.

The dyed cloth, being cut by a pattern to the size suited to the volume, is passedrapidly tluough a roller press, between engraved cylinders of hard steel, whereby it re-ceives at once the impress characteristic of the back and the sides, along with embossednesigns over the surface in sharp relief. The cover, thus rapidly fashioned, is as rapidlyapplied by paste to the stitched and pressed volume; no time being lost in mutual ad-justments ; since the steel rollers turn off' the former, of a shape precisely adapted to theJatter. Hard glazed and varnished calico is moreover much less an object of depreda-tlon to moths, and other insects, than ordinary leather has been found to be.

COBALT. This metal, being difficult to reduce from its ores, is therefore very little ,known, and has not hitherto been employed in its simple state in any of the arts; but its°kyde has been extensively used on account of the rich blue color which it imparts totdass, and the glaze of porcelain and stone-ware. The principal ores of cobalt arek°se designated by mineralogists under the names of arsenical cobalt and gray cobalt.he first contains, in addition to cobalt, some arsenic, iron, nickel, and occasionally sil- .er ; Ac. The oilier is a compound of cobalt with iron, arsenic, sulphur, and nickel.Among the gray cobalts, the ore most esteemed for its purity is that of Tunaberg inw eden. It is often in regular crystals, which possess the lustre and color of polishedaff 6 'i ^he s P ec ‘hc gravity of cobalt pyrites is 6'36 to 4-66. The Tunaberg variety^ orded to Klaproth , cobalt, 44; arsenic, 55-5; sulphur, 0"5 ; so that it is an arseni-a hi ® l * lers J however, contain much sulphur as well as iron. It imparts at the blowpipeUe color to bortix and other fluxes, and gives out arsenical fumes,anl 5 ore being picked, to separate its concomitant stony matter, is pounded fineSpr *! assed through a sieve; and is also occasionally washed. The powder is then2 om i on the sole of a reverberatory furnace, the flue of which leads into a long hori-Phu 31 chinme y- Here it is exposed to calcination for several hours, to expel the sul-l he ] ar senic that may be present; the former burning away in sulphurous acid gas,toarlf- beln S condensed into the white oxyde or arsenious acid, whence chiefly thewhoi etissu PP be <i Ibis article. This calcining process can never disengage theU Se j e these volatile ingredieats, and there is therefore a point beyond which it isdhent S l ° P usb ’ but tbe sma ^ quantities that remaia are not injurious to the subse-th eft °P ei 'ations. The roasted ore is sifted anew ; reduced to a very fine powder, andcal] e( j 1Xe d with 2 or 3 parts of very pure silicious sand, to be converted into what isels and 20 ^ 6- ^ 7 ith this product glasses are generally colored blue, as well as enam-Parefi P°tt er y ^ aze " In the works where cobalt ores are treated, a blue glass is pre-Thi s kh the zafl're, which is well known under the name of smalt or azure blue.Hess in' 116 * s ma( ^ e by adding to the zaffre 2 or 3 parts of potash, according to its rich-l brown Coba It>_and melting the mixture in earthen crucibles. The fused mass isBl °unted°f * Wbde h°t into water; and is afterwards triturated and levigated in millslump, \vl ° r K ,be Purpose. There remains at the bottom of the earthen pot a metallics Peiss, 11Cb Cunt ains a little cobalt, much nickel, arsenic, iron, &c. This is calledAs it i s .,

Impose of 5 0x y de of cobalt which has the coloring quality, the calcination serves theA finer coS! Z f. me . nt ’. as well as of expelling the foreign matters.

° r e in nit r ; ° . ox y de is procured for painting upon hard porcelain, by boiling the cobalt

lerent metat- 3 ^’ wb ‘ c b converts the arsenic into an acid, and combines it with the dif-a< hd, may fi 5 P resen t in the mineral. These arseniates, being unequally soluble in nitricas h i and th Se P ai ate ‘i >u succession by a cautious addition of carbonate of soda or pot-ior, and j s e p ar: ?, en ‘ ale . °I cobalt as the most soluble remains unaffected. It has a rosePoint, "p. Ukuy distinguishable, whence the precipitation may he stopped at the properuuded, with fro ° ve s °Iution should be much diluted, and the alkali should he cautiouslyThe eo^puum agitation.

jj e iron, cobalt' eS ’ r * cb * n n * c ^ e l> are exposed to slow oxydizement in the air, whereby. nickel conti arseIu . c > an< l sulphur get oxygenated by the atmospheric moisture, hutk'endcd beyond a*v S ln the meta Uic state. This action of the weather must not he1 ae : The ore hereh^ • 0tberw ‘ se tbe nickel becomes affected, and injures the cobaltSitudinal section _ r y „ 1Ilcrea s e s in weight, from 8 to 10 per cent. Fig. 291 is a

fir ®-b°ricks e hearU ""^ "

7 r>n level v?ith the.. 292 , a horizontal ^arth is composed ofIt is constructed for wood I^Va^ed in the roasll ^ n Cnt,° or

....CHS or tiles. The vapors and | ases d ® w c into the comm un dcr thetrough, the hues a a, into the channels b ^ tower s>f Altenher B5

poison chamber. See the representation ot the poi