688

IRON.

with occasional iridescence of surface. Neither nitric acid nor the blowpipe has anyaction upon it. Its specific gravity varies from 4-24 to 5-4 ; and its constituents are71-86 peroxyde, and 28-14 protoxyde, according to Berzelius ; or in 100 parts, 71-74 oimetallic iron, and 28-26 of oxygen. Assuming the prime equivalent of iron to bewith the British chemists, then an ore consisting, like the above, of two prime P r °P°'Itions of peroxyde, and one of protoxyde, would be represented by the number 116 =36; and would consist in 100 parts, of iron 72-4, oxygen 27-6.

Magnetic iron-ore belongs to primitive rock formations, and occurs abundantly 'J*Sweden, Dalecarlia, Norway, Siberia, China, Siam, and the Philippine isles; but it JSrare in England and France. It is worked extensively in Sweden , and furnishes an ex-cellent iron. *

The titaniferous oxyde of iron, or iron sand, is also attractable by the magnet. ^color is a deep black, with some metallic lustre; it is perfectly opaque ; its fractureconchoidal; it is hard and difficult to grind under the pestle into a dull black powd® jwhich stains the fingers when it is very fine; it melts at a high heat into a black ena®without lustre. All volcanic rocks contain a greater or less quantity of titanic iron- 0 jdisseminated through them, which may he recognised by its brilliant metallic lustre, aits perfect conchoidal fracture. ^

7. Fer oligiste, iron-glance, specular iron, and red iron ore.- —This ore has the colorpolished steel; and the light transmitted through the thin edges of its crystals appea r *a beautiful red. Its powder is always of a well marked brown-red hue, passing * fcherry-red, which distinguishes it from the black-oxyde ore. Its fracture is rough*vitreous in certain varieties; it breaks easily; but it is hard enough to scratch S' ass ',; 0 nusually contains from 60 to 70 of metallic iron in 100 parts ; the equivalent propo r j tof oxygen in the pure red oxyde of iron being 30 parts combined with 70 of metal-is a mistake to suppose any specular iron ore capable of yielding 85 per cent, of non,

100 parts of even protoxyde of iron contain only 77-77 parts of metal. ,

The compact variety comprises the crystals of the island of Elba , and of Fra®° n t j_the Vosges, which have a rough-grained fracture. It exists in very- great masses, c0tnling even entire mountains; in the cavities and fissures of these masses, the beacrystals so much prized by collectors of minerals, occur. j a r

The island of Elba is equally celebrated for its inexhaustible abundance of rich sp e .; ca Iiron ore, and for the immemorial antiquity of its mining operations. Fig. 581 is a ve

581

..slit!

IbioTai

section passing through the three workings, called Pietamonte (r>), Sangu ,na ^ e nd-Antenna (f), through an ancient excavation a, through the coast o, and the to the

ing at the canal of Piombino . The total height of the metalliferous mountainlevel of the sea, is no more than 180 metres, or 600 feet. hiancheH a ^

The rock which constitutes the body of this little mountain d l, is called . ^ chiefly

the workmen. It is a white slaty talc, slightly ochreous, or yellowish, consi °

of silica and alumina, with some magnesia. .... {

The ore of Antenna (f) is a very hard compact fer oligiste, of a ,,-ferous blo c H saspect. The workable bed has a height of 66 feet, and consists of Jneta i ro( ,j.y detr 1 'mixed confusedly with sterile masses of the rock ; the whole covered wi ^ t j,j s bed >-tus, under a brownish mould. From its.metallic appearance and tongnne. , ^ e ntir® *

called vena/errata, the iron vein. In Pietamonte the workable bed is co > jj 0 , v ocj> r 'of micaceous specular iron ore ( fer oligiste), with its fissures filled wi t j,j S pinThis bed rests upon the rock called bianchetta; the brilliant aspect oi orhas gained for it the name of vena lucciola. n( ] the WO»‘

The metalliferous hill d l, extends to the north-east, about a mile oe l . jn Cat ® 1ings D E F. The ore contains about 65 per cent, of iron, and is smei

forges. r ,nis extr^ d,na '

The following description of the figure will make the structure ot ln . jn2S . .

mine well understood, a, is a great excavation, the result of ancient w° r jn “ c()r resp on], 1 ; 2, 2; 3, 3, 4, 4, 5, 6, and 7, are roads for carrying off the rub *ence with the several working levels.