« iepriekšējāTurpināt »
ore contains from two to three per cent. of cobalt, but is quite free from nickel, though this last metal not unfrequently exists without cobalt. As a coloring material, oxide of cobalt is seriously damaged by the presi ence of oxide of nickel; for these oxides produce colors almost comple: mentary to each other, and therefore tending, by their admixture, to yield a neutral tint, as is observable when their saline solutions are united. The great advantage of working an ore of cobalt free from nickel must consequently be obvious to all. The Keswick mine is, nevertheless, almost abandoned at the present moment, through sheer inability to find a market for its produce; though for the finer kinds of porcelain, and for enamel painting, the oxide of cobalt procured from it is worth fully a guinea per pound.
"In the hope of drawing attention to a raw material at once so unique and valuable, we give the following original process for extracting pure oxide of cobalt from the Keswick cobalt ore: Having carefully roasted a quantity of this ore, at a full red heat, in a muffle furnace, for two or three hours, it is next to be reduced to a fine powder, and then digested in muriatic acid of the specific gravity 1.10, or thereabouts; and for this use the waste acid of the soda maker is well adapted, even though it may happen to contain arsenic and iron. After a few hours' digestion, the acidulous solution may be poured off and fresh acid added, so as completely to exhaust the roasted ore, and dissolve all the metallic matter in it; then mix the solutions thus procured; and, having thrown in a portion of powdered hematite, or other form of peroxide of iron, evaporate the whole to dryness; next pour boiling water on the dried mass, and stir in an excess of chalk, whiting, or finely-powdered marble, and preserve the whole at a temperature of about 180 degrees Fahrenheit, until all evolution of carbonic acid ceases; then add a quantity of sulphate of soda, and throw the mixture on a filter, when a solution of chloride of cobalt will pass through, containing a small quantity of the sulphates of lime and soda, but altogether free from metallic contamina. tion. This solution must now be supersaturated with a caustic lye of soda, and the mixture boiled for a few minutes, in order to insure the rapid precipitation of the oxide of cobalt, which, after careful washing with hot water, is to be dried and heated red hot, in a crucible, to give it the character suitable for the English market. One pound of Keswick ore will require about eight ounces of muriatic acid, of the kind alluded to, with two ounces of hematite, three ounces of chalk, and the same quantity of salt cake or dry sulphate of soda. The explanation of this process is very simple: in the first instance, the metallic matters of the ore-consisting of iron, cobalt, arsenic, copper, and perhaps, also, leadare dissolved by the muriatic acid; and, as all of these are precipitated by carbonate of lime, except cobalt, the chalk might now be added at once, but for the fact that the Keswick ore contains an excess of arsenic, which carries down a portion of cobalt in the state of arsenite of cobalt. To remedy this evil, peroxide of iron or hematite must be added, so as to insure the existence of an excess of peroxide of iron in the solution, as this, on the introduction of the chalk, will unite to the arsenic, and thus prevent the precipitation of any cobalt at this stage of the operation.. The cessation of all effervescence indicates that the chalk has ceased to act, and that the iron, arsenic, copper, and lead are no longer in solution, but have been displaced by the lime of the chalk. To remove this
lime, sulphate of soda is employed, since this throws down nearly the whole of the lime in the state of sulphate; after which caustic soda, or potash, will precipitate nothing from the filtered solution but pure oxide of cobalt. Although apparently somewhat complex in detail, this process is extremely simple and efficient in practice, and possesses, more. over, the advantage of being equally applicable to the treatment of speiss or arseniurets of nickel, from which pure oxide of nickel may easily be procured; using, however, much more hematite than the quantity indicated above, in consequence of the absence of iron in speiss. From this latter circumstance, it must be obvious that cobalt and nickel cannot be separated in the way just described; for, as has been stated, they both remain in solution after the employment of the chalk; and, indeed, no process has yet been published by which a perfect separation of these two metals can be effected. Ordinary Swedish zaffre contains, on an average, fifteen per cent. of oxide of cobalt, mixed with about three per cent. of oxide of nickel-which latter seriously impairs the coloring power of the zaffre. Hence it is that we have entered thus fully into this ques tion; for, as it is almost impossible to purify cobalt when contaminated with nickel, it is a kind of national disgrace to Great Britain that, having a pure ore of cobalt in the very centre of the island, our manufacturers are unable either to compete with, or so much as contest for the palm of superiority in the formation of zaffre."
Iron Ores.-England is so justly celebrated for the manufacture of iron and steel, that it seems not inappropriate to the present report to dwell somewhat at large upon the character of her iron ores and the products of her furnaces, noticing at the same time such iron ores from other countries as seem peculiar or remarkable.
The mean richness of the ores of iron in the South Wales coal basin is estimated at 33 per cent. These are the richest ores of England, the average in the Staffordshire district being less than 30 per cent, and those in other districts rarely rising above 25 per cent. This, it will be perceived by all who are familiar with the ore beds in our country, falls far below us, some of our ore yielding as high as 70 per cent of pure iron. In England every ferruginous clay stone is considered an ore of iron when it contains more than 20 per cent of that metal, and the loss of weight experienced during the process of roasting varies from onefourth to one-third of that of the original crude ore.
To effect the calcination of the mineral, it is piled up in long heaps over a strature formed of large lumps of coal. The fire is afterwards applied to the windward end of the pile, and after it has advanced a certain distance the pile is prolonged with the same material in the opposite direction. The ordinary height of such a heap is from six to seven feet, whilst its breadth at the bottom may be about fifteen or twenty feet. When the ore treated, as is not unfrequently the case, contains a large proportion of bituminous matter, it will, when once ignited, readily burn without the addition of any other material; but when it is not naturally combined with a sufficient amount of combustible ingredients, its place is supplied by the addition of a sparing mixture of small coal.
Instead of this method of effecting the calcination of the ore in open heaps, it is in many localities roasted in a sort of furnace or kiln, similar to that employed for burning lime. In this case, if bituminous, the addition of any other fuel to the mineral is unnecessary; but if not in itself
combustible, it is interstratified, at certain regular distances, with layers, either of coal or anthracite.
The preparation of metallic iron from its various ores depends on the reduction of its oxides by carbonic acid gas, when exposed to its action at a high temperature. With us, especially in the rich ore of the northern and eastern States, and where charcoal is readily procured, metallic iron, in its malleable form, is procured at one operation. In England, however, where charcoal is never cheap, and where the problem sought is to obtain the largest possible per-centage of metal from the ore treated, several distinct processes are resorted to, so similar, however, to those in use by the iron-masters of Pennsylvania that they need not be described.
Among the numerous models exhibited in the mining and mineral department, there was a beautiful representation in miniature of the furnaces and other apparatus employed in the Ebbw Vale Works, near Abergavenny, in South Wales. At this establishment, the gases evolved from the furnaces-and which, from the amount of hydrogen, carburetted hydrogen, and carbonic oxide gases which they contain, are highly inflamable, and capable of developing a considerable degree of heat by their combustion are conducted by proper pipes and channels to the various places where heat is required, and, being then ignited with a due admixture of atmospheric air, they afford a part, by the use of which the amount of solid combustible employed is considerably diminished. The model exhibited not only afforded an illustration of the way in which these gases were applied to the generation of steam for the blowing engine, but also showed the details of the arrangement by which, at the Ebbw Vale Works, the same agent is made to supply the amount of caloric necessary to heat the blast forced into the apparatus to the temperature of about 400° Fahrenheit-which is that at which the air furnished to hot blast furnaces is commonly supplied.
The model further showed the blowing machine itself, and the engine by which it was set in motion, together with its various appurtenancessuch as a large air vessel for regulating the blast, and the nozzles by which it was admitted into the hearth.
Mr. J. James, of Abergavenny, exhibited a model of his invention, the purpose of which is to facilitate the processes of drawing off of the waste gases, with a view to their subsequent employment for heating purposes. It had, however, never been tried, and great doubts were expressed in regard to its practical working utility.
To return to the main subject before us, it is well known that the principal sources of the iron of commerce are the oxides and carbonates of the metal; which, mixed with variable quantities of silicious and earthy matters, are abundantly met with all over Great Britain. The anhydrous peroxide of iron, or red hot hematite, which also frequently receives the name of specular iron-ore, is very abundant. It occurs both in crystalline and stratified rocks, as with us; but the purer varieties are always found in the older formations. There were some five specimens of the red hematite, crystallized, exhibited from the island of Elba, from mines worked by the Romans. Very beautiful crystals of it were shown from Stromboli, as also from Elba, Vesuvius, and Etna, formed by sublimation from the fissures in those volcanic regions. Some of the raw ore was exhibited in the Saxonian department, ground fine for a
pigment, and for the purposes of polishing
As a source-perhaps the greatest source of the metal, this ore is of importance. Some of the varieties-the specular, for example-have the disadvantage of being somewhat refractory in the furnace; but this inconvenience is entirely obviated by a judicious admixture of other ores. At Newcastle uponTyne it is used to mix with poorer ores; at Ulverstone, the same; while, from the furnaces at Cleaton, there were specimens of iron made from the pure hematite of the specular variety.
Brown hematite, a peroxide, also, is found abundantly in Great Britain; it differs from the red hematite in containing a certain quantity of combined water, and possessing a darker color. This ore frequently occurs here in a friable state; and, when naturally mixed with a considerable quantity of earthy matter, it acquires a peculiar softness of texture, and is known by the name of yellow ochre.
Granular iron ore was exhibited in some fine amorphous masses from Cornwall, and from Sutton county, Ireland. It is not common, nor much employed as an ore, in Great Britain. In Normandy, however, (from which specimens were sent,) in Burgundy, Lorraine, and Berry, it yields an excellent iron when washed, for the purpose of separating the lighter impurities. In what is called the oolitic form, it supplies the greater number of the French iron works. It is said, however, that when the beds of oolitic iron are found to alternate with calcareous deposits, the metal produced is very brittle, (cold short,) and consequently unfit for many purposes. This peculiarity is attributed to the presence of phosphorous, derived from the organic bodies of which chalk is principally composed, and which has the property of rendering iron extremely brittle, even when present in very minute quantities.
The octahedral oxide, or magnetic iron ore, is not used in England, though one fine specimen of it was shown from the Roche Rock Mine, Cornwall. In Sweden, however, it is the common ore in use, and from it the most approved Swede iron is manufactured. It occurs in large quantities in our country, furnishing the basis of much of the best iron. from our forges.
The iron ore most in use in England, and indeed throughout the three kingdoms, is spathose iron, or the carbonate of iron. It is found in rocks of very different ages, and is frequently observed to accompany other metallic ores-such as those of lead or copper. Carbonate of iron is, however, most common in gneiss, grey wacke, and the coal formations. The extensive beds of Styria and Carinthia occur in gneissthat of the Hartz is found in grey wacke; whilst the English deposits, from which the greater portion of iron manufacture in that country is obtained, are almost exclusively confined to the coal formations.
This mineral is frequently extracted from the same pit by which the coal is raised to the surface; and it either occurs in reniform lenticular septaria, embedded in clay found in the vicinity of the veins, or forms distinct seams, alternating with those from which the coal itself is extracted. The facility thus afforded to the manufacturer by the presence, in the same locality, of the ores, and the fuel required for their extraction, is evidently one great cause of the number of iron works in Great Britain and the extremely low prices at which iron is exported. The principal deposits of this mineral in the United Kingdom are those of Dudley, the products of which are chiefly sent to Liverpool; those of the neigh
borhood of Glasgow, on the banks of the Great Northern Canal; and those of Wales, on the seacoast.
All coal formations in Great Britain, however, do not produce iron The Newcastle district, which is perhaps the richest in the world in fossil fuel, yields so little iron that the furnaces which are worked in that neighborhood are principally supplied by ores brought by sea from a considerable distance. The French coal fields do not yield, generally, a sufficient amount of carbonate of iron to render its extraction a matter of much profit, with the exception of the iron works of Decazenville, in the basin of Aveyron.
In relation to this ore is a fact worth the attention of our iron masters: that ore which contains a small proportion of manganese-say from eight to twelve per cent.-is found to produce the best iron for making steel, while the presence of a larger per-centage of manganese is regarded as unfavorable. That a small proportion of manganese tends to liquify the slag is undoubtedly true; but what further use it can form it is hard
The bisulphuret of iron, or iron pyrites, although never treated metallurgically for the metal it contains, and consequently, properly speaking, not an iron ore, is, nevertheless, an important mineral on account of the sulphur which it yields. Its component parts are 45.74 of iron and 54.26 of sulphur. It occurs in cubical crystals in slate rocks and coal. fields. It frequently also accompanies the ores of other metals. Some crystals from the Isle of Elba, extremely large and beautiful, and presenting pentagonal dodecahedrons of four inches in diameter, were exhibited. From the Cornish mines and from Sweden some gigantic octahedrons were exhibited.
Antimony. The ores of this metal, so far as their products become an article of commerce, are obtained from Schemnitz and Kremnitz, in Lower Hungary, and from the island of Borneo. Antimony in the market is obtained from the native sulphuret of antimony, often associated with ores of copper, silver, lead, zinc, and manganese. To obtain it in its crude state, the ore is placed in crucibles, having a hole at the bottom, and these are inserted in other vessels; heat is applied to the crucibles from above, and the ore, which melts from its gangue, flows down, and is collected in the pot beneath, wherever it becomes solid. By this treatment the ore is not altered in composition, but merely purified from the infusible substances with which it is associated.
To obtain pure antimony, the ore is carefully washed in a reverberatory furnace until it has become oxidized, and then this product is fused with some reducing agent-such as crude tartar. Antimony is largely used, when alloyed with lead and a little tin, in the manufacture of printers' type, for which it is eminently adapted, both on account of its fusibility and hardness, and also from the circumstances of its expanding in the mould at the moment of cooling.
Among the illustrations of this metal were some specimens of regulus of antimony from the Bistroers Smelting Works, in Hungary; three varieties of crude antimony from the works at Maegdesprung, in Saxony; sulphuret of antimony from the mines of Saragossa; and specimens of Montanto and Pereta, in the province of Grosseto, Tuscany.
Silver. The silver produced in England is chiefly obtained by the treatment of the ores of lead. The silver of South America is princi