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QUICKSILVER.

VARIETIES OF ORE, ITS GEOLOGICAL OCCURRENCE, AND METALLURGY.  

THE recent discovery of quicksilver-bearing ores in this country, is a matter, the importance of   which, in a commercial point of view, is not yet fully recognised. So littlo, moreover, is known of this mine- ral, and its mode of treatment, that a record of the ex- periences gained elsewhere may probably prove use- ful in assisting in the development of this new colonial industry.

This paper is intended to show what geological conditions are necessary for the existence of quick- silver ores, the most favourable of those conditions and specially to point out the improved modern ap- pliances for its metallurgic treatment. Of the quicksilver ores in this colony little is at present known ; at Cudgegong it exists in talcose, and argil- laceous schists, indentical with the ores of Almaden in Spain, and California. Native mercury has been found at Frederick's valley creek, in the great water hole at Ophir, and at Muckerawa. Cinnabar ores occur in tho Abercrombie, and some good specimens have come from Queensland. Some years since, mercury was found near the Burning Mount Wingen.

Tho occurrence and mode of treatment are not so

generally known as might be desired ; and it is only of late years that the subject has been so carefully studied, as to enable us to treat the poorest descrip- tion of ores successfully and profitably : it is to Ger- many that we owe improvements in the methods of reduction, enabling su to work ores of ¼ per cent, and under. Water-dressing is a thing of the past ; poor ores will not wash, rich ores do not require washing: with poor ores the cost of extraction by fire is less than the cost of water-dressing. Particular attention has been called to the necessity of testing the ore before raising the bulk to the surface, and simple directions afforded. The immense quantity of ore that can now be treated in a simple and inexpensive operation has been made a prominent feature. The old aludel oven has been invented littlo over a cen

tury, but is being quito superseded in point of cosi of production, and magnitude of operation, by new and improved appliances. The section on thc varieties of ore teaches us that the quality of cin nabar ores cannot bo judged by the appearanco pre sented to tho eye. The purification of mercury and its chemical relations have been excluded, not being pertinent to the object of this paper.

To simplify the subject, and render it as intelli gible and easy for reference as possible, the matter is arranged under separate headings.

As tho description of apparatus used may alone be unintelligible, it hos been thought desirable to fur nish drawings of the most approved plans in UBO.

The information contained in this article is mostly derived from tho works of Percy, Muspratt, Miller, Keri, the British Encyclopaidia, Dana, Watts, Knight, and some other British and foreign sources ; and it is hoped that tho compilation and arrangement may prove moro useful than the materials can possibly do while scattered in hooks which to many are unknown

or inaccessible

1. VARIETIES OF QUICKSILVER ORES. Cinnabar.-Colour, bright vermillion. Iodic Mercury.--Reddish Brown.

Selenid of Mercury.--Dark steel grey.

Horn Quicksilver.-Light yellow or greyish.

Hepatic Ore.-Liver-coloured, with bitumen and

other impurity.

It also occurs in chemical combination with grey copper, containing antimony and silver. Likewise, native, and as an amalgam with silver in variable proportions up to 86 per cent.

2. MODES OF OCCURRENCE-SHEWING IN WHAT FOR

MATIONS THE ORES ARE KNOWN TO EXIST.

Tho richest ores, particularly cinnabar, associated with native and horn quicksilver, occur, not as lodes, but in beds, in sedimentary formations, not younger than the carboniferous. Cinnabar, in Idria, occurs in rocks of carboniferous formation. In Almaden, in Spain, it forms partly lodes, partly layers, in Devonian rocks-consisting of clay -- slates, and quartzitos, containing iron pyrites. In Huancavelica, in Peru, in sandstone and clay beds, of the carboniferous age. According to Silliman, it is found with bitumen, seldom with iron pyritos, in irregular lodes, with quartzose and sparry gangues; sometimes in cal careous beds, but seldom in earthy beds of chalk age, as botween tho bay of San Francisco, and Monterey,

in California.

Of tho deposits of cinnabar, w layers, tho more important aro confined to transition and carboni ferous Btrata, as at Idria, Almaden, Huancavelica, California, &c At Kaernthon, at Kuppel, in green and red metamorphic slate; at Bucholz Proben, and Richenda, in transition slates ; in Bohemia, at Hergovitz, and Komarow, with iron ores, in tran- sition rocks: only unimportant beds occur in the youngest geological formations-for instance, Conna, in Portugal, in alluvium; at Montpelier, pleisto- cene, calcareous sandstone and marl, occurring mostly in native state, with small quantities of chloride and iodide. The only formations above the carboniferous, where quicksilver occurs, are in the lias at Dobshaw, in Hungary, where cinnabar and "Fahlerz" (grey copper) occur in a lode; and in the chalk at Solvena, in Italy. The most important beds are almost wholly free from admixture with other ores, ex cepting iron ores and particularly iron pyrites. In lodes, a way in which quicksilver ores, unlike other metals, seldom occur, other ores are more abundant. Quicksilver with Fahlerz, grey copper, occurs in diorito, at Kremnitz in Hungary ; in porphyritic diorite, at Schenmitz; in talcose schist, at Szlana ; in suphotide with cinnabar and iron pyrites, at Kottemback and Porcas. At Dobshaw, Fahlerz and cinnabar occur in lias; at Rheim nlatz there is an exception to the rule, as it ocexu-s with Fahlorz, iron pyrites, copper pyrites, malachite, nativo silver, anet blue carbonate of copper in a clay lode in carboniferous formation. Similaily in Sie benbürgen cinnabar occurs with a little blendo and galona, in lodes traversing trachyte and Carpathian sandstone. At Vallalta in the Venetian Alps, cinna

bar in diffused through various rocks, viz : Conglo merate, red sandstone, red quartz, porphyry, talo slate, blaok clay slato, and gypsum. In Tuscany cinnabar penetrates a bod of ordinary mica schist, passing gradually into -white silky talcoso schists, penetrated by many quartz voins. At tho Rhonard Mino in tho "Westphalian Alps, cinnabar has been found in tho Devonian formation. Beyond doubt the largest deposits of cinnabar occur in tal- cose and argillaceous schists, generally of a yellow or ochreous character, as at Almaden, in Spain, in California, and at Cudgegong in this colony ; and mostly in tho carboniferous formations. A dark brown or black schist is occasionally met with, strongly impregnated with native mercury and cin- nabar ; but with but little visible.

3. DRESSING OPERATIONS.

Most of the ore is treated without dressing, as will be hereafter shewn, since new modes of reduction have been adopted, under which ores containing as little as one eighth of one per cent., aro now treated on a large scale to a profit. Poor and finely dissemin- . ated ore is treated direct to avoid the cost of dressing, and tho loss that would result therefrom. The inexpensive operations adopted for the reduction of very poor ores, result in a loss, bearing a relation to the quality of material treated; as will be shewn in a table, compiled by Muspratt-tho result of a large experience. But, with a rich quality of oro, it is sometimes desirable and economical to subject it to more expensive, and moro perfect distillation, to avoid that percentage of loss which would otherwise result. Hence, the ores containing a notable quantitj' of massive cinnabar are carefully sifted, hand-picked, or occasionally washed. Tho fine crystalline cinnabar saved therefrom is treated in a closed retort, specially constructed for tho purpose, by which about 98 per cent, of the assay contents are extracted, and the remainder is treated in the large way. The pro cesses will be here described.

4. TESTS ADOPTED FOR ASCERTAINING PER CENTAGE

OF ORE BEFORE TREATMENT.

Few things are more important for ensuring the success of a quicksilver mine, than to have at com- mand a ready means of ascertaining the quality of the ore produced in different parts of the workings. "When we take into consideration that tho ore exists

in so may different forms, and that many materials may be very rich without a particle of the ore being visible to tho eye, even with the aid of a glass, such a necessity becomes more and more obvious.

It being previously ascertained hotu poor an oro will pay to treat, it must bo evident than the ex traction of an ore inferior to that standard, involves a waste of labour (i.e. money) ; while anjr ore of higher standard, if left untouched in the mine, im plies waste of valuable material. If, therefore, tho ore is not tested in tho progress of the workings, both these sources of error and loss may be expected to aiise, and worse than all, to be perpetuated.

But by neglect of this precaution a far greater trouble immediately follows : the ore raised indis criminately, will probably be subjected to the pro cess of reduction indiscriminately. Not knowing the percentage of metaUic contents before treatment, it is of course impossible to ascertain if any loss has aiisen in the reduction, besides the risk of treating material which may be worthless. It is plain that if the precaution be taken, and a loss should occur in reduction, the cause may be at once ascertained, and a remedy supplied ; while in the other case the loss may be continuous without its existence being suspected.

To test a moderately rich ore, take from five to fifty ounces, mix with half an equal weight of black flux, distil with slowly increasing heat, in an earthen' or iron retort, or tubej-let your tube be at least BÍX or eight feet ; condense in wet linen sacks tied at the end of the tube, and dipping into water: the underpart of the retort neck must be kept cool, by wrapping round it wet rags or paper. At close of operation, tap retort neck, to detach adhering glo bules of quicksilver ; dry the quicksilver with quick lime and bibidous paper, and take the mean of four or five tests. Take special care, in case the end of tube should dip in water, that in the event of any regurgitation, on tho cooling of the retort, only a small quantity of water can be drawn up, otherwise an explosion will "probably result. This danger may be easily guarded against, by so immersing tho end of tho pipe that, on the least suction, air will got access. Avoid too high a temperature, or the cinnabar will sublime. Tho fluxes generally used oro iron, alkalies, lime, &c. Alkalies decompose cinni bar at a lower temperature than iron or limo. Tho poorer the ore, the less accurate will be the result of the test. In ores containing a tenth of one per cent, up to half per cent, the loss is considerable. The yields of mercury on distillation, from different quali- ties of ore, have proved to be as follows : Ores containing [Percent of actual contents.]

0.01 to 0.1 mercury, yield from 0 to 47 0.1 to 0.2 " " 41 to 59 0.2 to 0.5 " " 02 to 91 0.5 to 0.6 ,. " 86 to 93 6.0 to 24.0 " " 95 to 98 24.0 to 48.0 " " 96 to 98

48.0 to 86.0 ,, " 95 to 97.

The composition of cinnabar by weight is "203 mercury to 32*2 sulphur, so that every 100 grains of pure cinnabar will contain a little over 86 grains of

mercury.

At the mines in Idria (in Camiola) an oven is employed to test the quality of the ore before treat

ment.

Eight trials are made on each assay. The oven is 6 feet 8 inches in height ; the side containing grate 36 inches broad. At each side aro 13 openings for re ception of tubes, ff, for testing;.length of asconding hoarth, /, 3 foot ; fire bridge 10 inches above bars, à; grate'15 inches broad, 22 inches long; ontrance into flue, t, 3 feet 3 inches above the ground at h ; tho eight middle tubos only, on each sido, aro used, as it is found that those nearest tho firo and nearest tho flue do not givo trno results. In each tube is placed £ lb. of powderod oro, mixed with two or threo spoonfuls of powdered limo. Tho process is ended when tho empty tubes aro strongly red-hot, and tho mean of tho eight trials is taken as a re sult. Tho bulk when operated upon should yield the result of this avorago. Tho precautions as to condensation, previously explained, have to bo rigidly observed. For this class of ore, tho Idrian test process is most gonerally approved.

Fahlerz ores which frequently contain quicksilver, and sometimos cinnabar,. accompanied by other metals, are tested in Hungary as follows :-tho ore is mixed with an equal quantity of iron turnings, heated in a small glass retort, supported in an earthen pot in a small galley oven. Tho quicksilver distillod thorefrom condenses in tho neck of the retort, and may bo detached with a slight tap, or with a wisp of straw, united with any that may havo come over, and weighed. Tho residue is found fused to the glass.

Lastly, poor quicksilver ores, amalgams, residues from retorts, native mercury, &c., should bo treated with aqua rogia, filtered, washed, evaporated to dry noss, (on water bath,) mixed with three times its weight of black flux, and distilled in a glass rotort at a very low temperature. The mercury which has been converted into a chloride, is much moro volatile than tho sulphide Iron and limo would not do, as they require a high temperature. Tho black flux must bo intimately mixed-any limo pro -sent, (as from rotort residues), may bo removed with

acetic acid.

{¿¿J;-. 5. METHODS or EXTRACTING QUICKSILVER.

Roasting in heaps in tho opon air, (Hungary) ; in pit ovens, (Idria, Spain, Tuscany, Vallalta) ; in revorberatory furnaces, (Idria) ; distilling in iron retorts, &c. Tho ohoico depends on tho quality of tho oro, richness, scale of working, cost of labour, &c. Smalls aro usually worked in closed vessels, or reverboratory furnaces ; coarse ore in pit ovens.

6. CONDENSATION OF QUICKSILVER VAPOUR..

Various methods of condensing haye been adopted at different mines, but this department of tho work is still susceptible of improvement. Earthen or iron receivers aro used at Rheimbaiern; pear-shaped earthen vessols, called aludels, in Spain; conical receivers in Liebenburg ; masonry chambers, in Idria, Spain, and California ; iron tubes, cooled by water, at Idria ; wooden ones, at Vallalta ; and the new method of Formbar s, of condenser with Cagnia dello and Sucker. Chambers are preferred to aludels, but tubes cooled with water are considered

still better.

In erecting quicksilver plant, and proportioning tho condensers, it must bo borne in mind that 200 lbs. of mercury in vapour, will occupy a space of 460 cubic feet, or, in other words, a cubic foot of quicksilver vapour contains nearly half-a-pound of metal. This fact is most important, because inattention to it may bo productive of great loss, and dangor. In treating tho material in closed retorts the knowledge of this fact teaches us to leave as little vacant space as possible, in .the retort, as that space will at the close of tho operation contain mer cury vapor unless suction is employed to draw it into the condensing chamber. Suppose for instance tho rotort is 6 feet in length, 15 inches high, 18 inches broad-the tray containing tho material for treat ment, 3 inches deep. You have then a vacant space of 9 cubic feet. If we then treat one hundred pounds weight of cinnabar oro, containing 6 per cent, of mercury, the probability is that we may obtain 2 lbs mercury, the remainder being in the form of vapor on opening the rotort, and escaping into tho air. Take, however, the case of ono charge contain ing 50 lbs mercury : under an injudicious application of heat the whole of this may be converted into vapor in a very short .time ; and if an excessive heat bo maintained and tho arrangements for conden sation aro not of the most perfect character-this vapor will require at least 100 feet of space, until it has had time to condense. If thero is not that space for tho accommodation of tho vapor (under tho circumstances abovo described)-it will force its way into the atmosphere. Tho inhalation of this vapor is exceedingly dangerous to the workmon. Tho main points aro tho regulation of tho heat, which should always be low ; and the perfect cooling of the chambers through which tho vapor passes.

7. QUICKSILVER. SOOT, OR " STUPP."

Some chemical reactions always tako placo, pre venting tho whole of tho minorai hoing converted into a metallic state. " Stupp " is an intimate mixture of finely divided quicksilver, cinnabar, calomel, oxido of mercury, soot, &c, which doposits on tho -walls of tho condensation chambers or retorts, and in the tubes ; the metallic quicksilver ia separated from it, at Almaden, hy manipulating it on an inclined plane, whereby most of the metallic quicksilver flows off. Tho material is then treated with hot ashes, brought in contact by means of a perforated scraper, to disengage a further quantity ; and the residue utilized in an oven specially con structed for the purpose. Tho theory of tho pro duction of "Stupp".is complicated, but it is neces sary to state that the presence of cinnabar with it, indicates that too high a temperature has been em ployed 5 and the oxide is occasioned by atmospheric air, coming in contact with the hot vapor. Accord ing to Proust, the composition of quicksilver black, found in tho earthen alúdela, differs from that found in cast iron pipes used for condensation.

The composition is as follows :

Eartlion Cast Iron aludols. pipes.

Finely divided morcury

ana oxido . 66 per cent. 44 per cont. Chlorido of mercury .... 18 " 3.3 " Sulphide of mercury .... 1 " 6.3 " Sulphates] of iron and

alumina, potassium, am monia, HmOjCarbon, sul

phuric acid, and water 15 " 46.4 "

100 " 100. "

In Borne cases a larço quantity of thia material is formed, necessitating its frequent removal from tho pipeB to avoid obstruction.

8. RETORT OVENS.

Tho decomposition of cinnabar, by dosulphuration in »ctort ovens, is a process which, only pays with the richest ores, of winch thoro is visually a small yearly production. Itdomands a larger expenditure of time, labour, and fuel than tho roasting mothod, since the oro for decomposition requires a higher and moro protracted temperature. In consequenco of tho confined space in tho condensers, tho condensa tion takes placo with difficulty ; tho material how ever is more perfectly treated than by tho roasting process, and tho workman have moro protection against fumes. Tho ovens constructed for continuous uso, and omployed at Lansburg, Siobonburg, Cali fornia, and Tuscany, pormit cheaper and larger pro duction than tho older form of galley oven, adopted only for occasional use, and employed in tho old methods, at Rheimplatz, Siobonburg, and Bohemia. In comparison with tho pit oven, tho production of tho ordinary retorts is loss, because owing to tho largo dimensions of tho retorts, the heat cannot per fectly penetrate, and tho quicksilver vapour escapes with greater difficulty. Roasting ovens as used in California obviate tins difficulty ; but are more ox ponsivo than pit ovens, on account of tho greater consumption of fuel, tho requisito comminution of the ores, and the necessity of perfect.admixture with the decomposer. At Rheimbairn, poor and rich cin ! nabar ores aro treated in iron retorts with limo.

I Retorts are 3 feet long, and IC inches broad in tho

belly, flask shaped. 30 to 50 of such retorts fit in two rows ono abovo ariother, on both sides of tho

J furnace (fig 2) in the vault of winch holes are left,

communicating with earthen receivers, B, outsido tho furnace ; these rocoivors aro 14 inches long-luted contain water, and aro emptied every ton hours. Each of these retorts contains from eighty to one hundred pounds of ore, (rich and poor,) mixed with 15 to 18 lbs. bumed crushed lime. Tho Bro of wood or charcoal is kept going ten hom-s, tho receivers are then emptied into earthen vessels filled with water, and washed. The quicksilver is saved, tho " stupp" gets washed away. Tho average production of 80 or 100 lbs ore is 1 lb quicksilver ; the fuel consumed

20 to 30 lbs.

At Lansburg to effect moro convenient charging and better condensation, tho continuous apparatus of Uro fig 3 is employed ; the working of which

treats from 6 to 7 cwt. ovory throo hours. « is a retort over a fire, set in masonry, furnished at ono end with a tuho b, and on the other with an air-tight plato. / is tho opening of tho tuho b, for removal of tho "stupp," through a screw aperture. Cis o cast iron condenser 18 inches in diameter, 20 feet long, containing water :-the tuho b is fitted with a water valve to prevent tho water hoing sucked up. Around the condenser is a wooden trough through which a continuous stream of cold water is always flowing. The condonser is furnished with tubes for conveying tho condensed quicksilver into a closed vessel, from which it is run into an iron chest, tho top of which is secured by a padlock. There is an iron float wlrich shows the lovel of tho quicksilver. Notwithstanding the continuous flow of water, tho apparatus has boen condomned in practice, as with any irregularity in the application of heat, tho vapors expand, the lutes will not hold, and the mercury escapes

into tho air.

At Siebenburg cinnabar is worked in ovens superior to tho old galley ovens, with earthen retorts, causing tho completo expulsion and conden sation of all the quicksilver ; the consumption of fuel is loss, tho loss of mercury less, and they are con tinuous. The quicksilver is discharged into a woodon cheBt 8 feet long, 1 foot wido, 9 inches high; it stands in a water trough, each three retorts have ono chest. Limo usod 25 to 30 per cent. ITiring occupies 2j to 3 hom's.

At New Almaden in California, quicksilver is dis tilled with lime in iron retorts, using wood fuel : also by roasting. 400 lbs of rich oro, 40 por cont., is mixed with 600 lbs bumed limo, heated to faint redness, 21 to 32 hours, according to quality of wood. The vapour is condensed in vertical conical receivors, kept cool by a stream of water; tho quicksilver is drawn off after every oporation. For 100 parts, 40 per cont, ore, 100 ports

of nir-driod wood is used.

Vortical retorts, 8 toot long, have boon tried, con taining 125 lbs. oro, mixod with lime, working off in four hours, and discharging vapors under water; but thoy havo not given satisfaction. To increaso the rate of production larger roasting retorts have come into use, "3 feet long, 2^ foot wide, which work off the same quantity as tho vertical retorts in two hours. ^ Experiments made for tho sake of com parison, with ordinary retort ovons, and pit ovens, with continuous uso, show that in tho reduction of ono ton of oro, tho cost by tho rotort oven is 12 dol ara moro than by tho pit oven ; so that unless the ©tort oven extracts at least 30 lbs. moro quicksilver

thtin the pit oven, the work may ho performed more economically in tho lattor. Hence tho retort oven is used almost wholly for the reduction of oro of tho finost quality, or picked oro.

9. BOASTING IN FURNACES, KILNS, &c.

Tho rationale of tho process is that tho sulphur is converted into sulphurous acid hy roasting with access of air, provontion of oxidation of morcury at high temperature, thus ensuring its romoval in tho form of vapor. The various kinds of apparatus ora ployedfor tho operation aro, stadels-pit ovens, with intermittent or continuous uso, and rovorhoratory furnaces ; for condensation-tubes, chambors, earthen vessels, and aludcls are used.

Roasting has tho advantages of cheapness, groater production, smallor expondituro of fuel and timo ;: but its disadvantage is, that tho condensation is not perfect, on account of tho hot products of combus tion ontering tho condensers at tho samo timo as tho quicksilver vapors, and causing a strong draught.

A. ROASTINO IN STADELS.

This method is principally employed in tho treat ment of Fahlorz ores, containing quicksilver; but on account of the enormous quantity that may be troated by this process, tho extremely small cost of the operation, tho small per contage of loss| and tho simplicity and inexpensiveness of the apparatus, it is desirable to describe tho process. At Altwasser and Iglo, in Hungary, the method is employed in roasting Fahlorz ores containing quicksilver, but tho quicksilver is a byo-product. Tho stadcl is simply a brick chamber open at tho top, 42 feet long, 20 foot broad, 4¿ feet high, tho bottom of tough clay firmly stamped ; at a height of 6 or 8 inches abovo tho ground thero aro several draft holes, G inches high, and 14 inches long. From the bottom, up to the level of tho air holes, poor residues, not thoroughly exhausted and small oro, aro put ; abovo that aro ranged, 3 feet logs, at right anglos to walls of stadol, so as to canso a smart draft ; in the middle of tho stadel aro placed throe wooden logs, joining each other at tho top, to assist a draft. Charcoal is then strewn over the stadel, thon layers of mid dling and best ore, mixed with any oro which has been previously treated, but not thoroughly ex hausted, in a layor 3 to 5 inches high ; upon this layer, arranged in rows round tho walls, 2 feet broad and 6 inches thick, is another layer of slimo oro, or smalls, for chocking tho draft ; tho middle being Ailed with poor ores, 6 inches high. Tho stadol is thou filled up with middling and best ores, to a height of 4 inches above tho surfaco of masonry falling, however, towards the middle, so as to leave a depression of about 4 in. below surfaco of masonry, Two openings in tho sido of tho stadel servo for charging and emptying samo. To keep down the loss as much as possible, tho richest ore is put in the middle, tho poor near the draught passages. Fire is kindled by putting lighted charcoal in the draught holes ; it generally spreads uniformly, and sets fire to tho ore rich in sulphur. The quicksilver vapour formed. condenses in drops, on tho upper colder layers ; hot places which would evolve quick silver vapour, and glowing parts, aro care fully covered with fresh oro. Roasting occupies about 3 weeks ; tho upper layor containing mor cury is cautiously removed with shovels, washed in wooden tubs, and the mercury collected in a hand trough. The mean por centage of 1.63 mercury, as found by testing, yields by this method 94 per cent, of assay contents, so that for this class of ores it has driven all other methods out of tho fiold in point of cheapness. Lately 17 round stadels on a largo scale have been introduced, each containing 150 tons of oro, in layers 22 to 24 inches high, giving an aggre gate of two thousand five hundred ions for treatment in ono operation. After removing tho upper layers

as deep as ono can seo the mercury, the ores in tho under part of tho roasted stuff are assayed, and have occasionally to he treated again. 10,000 lbs. oro (100 centners) con taining 1.64 per cent, mer cury hy assay, yield 1.36 per

cont, metal. The cost of

working 1 centner (100 lbs.)

ore is 8.30 kreutzers or about

3d. Tho expense of extract ing 100 lbs. mercury is 10 florins 23 Itreutzers, equal to 16s. Gd. sterling.

B. - BOASTING IN PIT

OVENS.

By this process a larger extraction of mercury, and

moro porfocfc consumption of fuel are ensured than hy A (stadols). Lumps arc better than slime, or smalls, for this method ; tho latter, unless worked in a reverberatory furnace, must bo introduced into the pit ovens, on clay or cast iron trays, being pre

viously mado into cakes with clay and dilute sulphu

ric acid. There aro two kinds of pit ovens, con tinuous_ and non-continuous; former being most economical in use. Pear-shaped earthen tubes, or aludels, (as at Almaden), aro used for condensing in tho first stage ; tho vapour thence passes into .well built masonry chambors, dry, or cooled outside with wator, (the last named plan boingadopted at Idria, Ripa, Almaden, and California). Water is rarely al lowed to stroam into tho chambers, as at Castellaraza ; or tho vapours aro conducted into canals, or tubes, coolod with running wator. Chambers being very spacious and expensivo, and absoi'bing somo quan tity of morcury vapoui', have boen substituted by cast iron tubes, coolod externally with water, (as at _ Idria),. but as these woro found to bo easily attacked by acid vapours, thoy havo been advantageously superseded by wooden tubes (as at Vallalta). Formhals latoly invented a condonsing apparatus, in which mercury vapours are drawn by suction, through a ,systorn of water-cooled iron pipes, and then brought into contact with wator.

1. Pit ovens not continuons in their operation : Those must bo cooled beforo emptying, thereby causing loss of much timo and fuel :-the changes of temperature crack tho walls of the chambors-there by allowing tho morcury vapour to escape

(«) Tho Spanish bustamonto or aludel ovon is of this class ; but as thoso havo boen much impi'oved on, it is tmnocessary to describo them in detail. Thoy consist of a fire-placo or grate, a pit containing the ore over which tho heated vapours travel ; tho pro ducts of combustion and morcury vapours thon pass through earthen aludels, 10 inches in bolly, and 6 inches wide at the end, {joined ono in another, and arranged in six rows, terminating in a condonsing chamber. (A plan of this oven may bo soon in Miller's Chemistry.) The longth of entire apparatus

is 65 foot :-a strong fire is kopt going ton hourt' during which time frosh supplies of oro are admitted from above ; tho oven is left to itself diuing tho night, Aro stirred up noxt day, allowed to cool on third day, and cleaned out on foni'tli. Tho process is expensive, loss of quicksilver considorablo, aludels freq uontly break, and tho method is unhoalthy for tho workmen. Tho chargo of oro is about 12 tons.

(/>) Tho old Indian ovens, (Leopold's) : Those also havo boon superseded by other and bet tor ovens, though thoy aro still used in sovoral - of tho Spanish works. Tho quantity thoy can treat is far greater than tho aludel oven, but tho yield is not so good. Tho furnaco is ol' masonry ; tho liro-placo in tho middlo, and directly over it some 50 or GO tons of oro aro laid in such a way as to allow tho heat to play through: thoro aro six or sovon condensing chambers on each sido, through which tho fumes pass with thc vapour : those chambers communicate alternately by openings above and below, and at tho bottom of oaeh chamber is a gutter, mado air-tight with wator, into which any condonsod morcury can flow to tho receiver. Tho pit containing tho oro is fur nished with throe arches ; on tho lowor ono is placed tho poorest oro ; on tho middle ono tho richest, and some smalls ; and on tho upper, dust and slime on earthen trays. A cherry heat is maintained 10 or 12 hours, aided by powerful draught. It is thon allowed to stand'five or six days, cleaned out, swoop ing walls thoroughly, and working tho " stupp " in next chargo. Tho avorago richness of tho oro worked is 3.26 per cont., tho yield of mercury 2.3G por cont. This largo loss however, can bo avoided, by tho uso of some of the improved furnaces to bo presently described.

In practico it is found that coai-so oi*e, and smalls or slimes aro bettor worked in scparato ovens ; a french ovon, invented for tho latter, is in throo com partments with 1800 trays, oach tray contains 40 lbs. slime, from which 85 to 90 per cont, of the contained morcury can bo oxtracted. Sometimes coarso ore is worked in Hahners continuous ovens, and smalls in Albert's rcvorberatory ovons.

For four years, cinnabar, occurring in carbonato of iron stono has boon worked at Miorco, in tho pro vince of Oviedo in North Spain, in Idrian ovens, with 1G instead of 12 condensing chambers. Tho dotails di (1er but slightly from thoso alroady described-tho only important foaturo hoing that tho ore only con tains half per cent, of mercury. 3000 tons of ore are worked yearly, and produco 12¿¡- to 15 tons morcury.

2. Pit ovens for continuous tvorkiny, and with condonsing chambers, or iron, or wooden condonsing tubes, or with water condensation, and uso of a suction apparatus (Formhall's.)

(«) Ovens with chambors : Lately at Idria Hahn er's pit ovons have been used for ti'oalmont of larger oro, containing 3 to 4 per cont, morcury instead of Loopold's ovons. For poor ores containing J to 1 per cent., thoy uso rovorbatory furnaces.

Hahnor's pit ovens consist of a cylindrical oven pit l-l metros high, (tho meti'o is 39 inches) 1.2 metro wide ; at tho top of tho cylinder is a funnel for continuously supplying the oro and fuel, in such proportions as may be found necessary ; below is an oblique grato, thi*ough which tho exhausted ore ia allowed to fall, by partially withdrawing tho bars. Tho morcury vapour passes thence successively into four condonsing chambers 6.7 metres high, 1.8 motres broad, and 2.2 motrcs long ; thence into a fluo containing 3 compai-tmonts. Tho condonsing chambers aro closed abovo, with an iron plato, on which continually flows coldwater. At tho floor of each of tho condensers is an opening, through which tho mercury flows into a receiver.

(ô) Ilahcor's improvod ovens : At Castollaroza, in Tuscany, Hahnor's ovens have boon furnished with a much improved condonsing apparatus.

(«) Oven pit 2.2 metres high above tho grato b,

and 0.1G metro wido.

(c) Canal 1.2 metros long, 0.1G metro high, lead ing to 3 masonry chambors cl of 2 metro high, and 0.75 metro wide, in communication.

(c) Hemispherical floor from which tho condensed mercury escapos, through / into the vessel ff.

(li) Long canal 0.3 metro high, and 7 to 7J metro long, abovo which in tho horizontal part is a body of

wator.

(«t) Condensing chambers, 1 metre wide, 1.5 th high, into which at tho mouth of the pipe, R, a jet of water plays. .

!w) Canal for escape of carbonic acid. lp) Fluo, 19 metres wide.

With this oven it has boen found profitable to work ores containing only 3 or 4 per mille ; it collects much rich "Stupp" in tho first three chambers, while much puro and fluid bitumen, and a creosote like oil collect at tho canal under water.

(c) FormhalTs oven : A very complete, compact, and economical apparatus in use at San Francisco. Tho continuous pit oven, with grate, is closed abovo,. Tho charge is introduced through a sido passage underneath tho closed ovens mouth; a tube opposite to this conveys tho mercury va pours into tho condensers ; this consists of a cast-iron cylinder, in tho upper half of which is a number of upright tubes with# seivo-like bottoms, and surrounded with flowing wator. Through those tubes tho morcury vapours pass, and become for tho most part condonsod, collecting at tho bottom of tho cylindor. Tho gases and incom bustible vapours escapo, through a single exit, in tho under half of tho condenser, through a sido tubo, into a hermetically closed spaco, in which a caghia dello moves in water ; this removes tho gases and vapours, and brings thom, in theil* passage through tho windings, into intimate contact with water, causing as porfoct a condensation as possible. Tho uncondensed vapours from tho cagniadelle pass through a tubo, curved downwards at tho end into a

receiver partly filled with water,-hore pass through tho water, and oacapo finally through a tubo in tho roof of'-tho receiver. Thia apparatus obviates tho inconvenience of ordinary condensers of morcury vapours. Whilst tho walls of tho condensers of tiio now Almaden, absorb about 4000 lbs. morcury, this absorbs none. With tho continuous working- of tho lattor, tho expansion and contraction of tho oven is avoided, ¡ind thc timo of reduction lessoned. Whilst tho old brick chambers have boen worked with a consumption of 100 tons fuel per week, costing about 30,000 dollars, thc new apparatus of similar capacity costs not over 4000. Tho cost of reduction is scarcely half of tho bustamcntc and aludel oven.

(rf) Ovens with condensation tulles at Vallalla : in Venetia, pit ovens, 35 feet high aro used. Vapours

pass Hiiries.sivdy into li, ¡¡nil c, thence into il, wot wood lillies ; clumibcrij <\ f, and ij, wood tubo //, chambers ¡, and /<., through / and ni, into wasto tube o, communicating with water drum , ot' wliich tho p.nuclc snout, //, is provided willi water, hy tho chan nel, j). The drum uncles tho combustion products from tho oven, and thc hist trace of vapour is con densed in the (-humid ol' thu water drum, liv this perfect and economical apparatus, thc doublo oven will decompose I ¡J l<> 20 tons of oi-u, by tho aid of four mon, in twenty-four hours, with scarcely 8 cwt. fud, and without injury to workmen. Ores con taining only ono riijhth. nf uar per catt, aro treated profitably by this method.

In this colony, ores containing ono per cent, of murciiry, if worked by this pi'oeess, would yield, for every charge of twenty tons ol' oro, .lOlbs. of mercury, worth 2s. per

pound_'. i'll 0 0 "While tee espouses would be for

liaising and Mining, 5s. per ton £5 0 0 I jabour of four men, 7s. (id. per

day.-_ 1 10 0 Fud, say 1 ton. 0 5 0

- G 15 0

Leaving a profit for thc days work

of. £37 5 3 On tho working of a single furnace, with this poor quality of ore.

C.-ROASTING IN RKVUUHEKATOUY FUIINACES.

This mothod is essentially for smalls, which would choko draught in pit ovon.

1. Continuous oven used at Idria : Albert's rovor boratory (fig. G), givos good results.

(«) Flat brick hearth, for reception of ores, in thrco divisions. ",

(b) Opening for admitting 2 J tons of ore, in lumps of-2 or 3 cubic inches, first placed in division fur thóst'.froni tho lire, advanced later to socond and first divisons, and shovelled about for throo hours.

(c) Outlet botweon hearth and firc-placo for dis charging tho ore.

(d) Front chambers.

(<..) Tubes from which cold wator trickles on tho cast-iron condenser tubes, /, /.

(rf) Condonsing chambers which communicate through tho tubes /, with a fluo k, divided by par

tition walls.

From ff, tho mercury vapours pass through tho canal r, into upper condensing chambors ;/', //', into tubes,/',/', into chamber rf', through fluo k into tho air. Most of tho mercury vapours aro condonsod in tubos /', /'.

(m)' Closable opening loading to condensing

ohiunbers.

(5) Crano for opening and closing hopper, b.

Stupp collects hi tho tubes, wliich aro regularly cleaned out. Tho doublo oven works daily 10 tons of smalls. Of tho assay contents about -10 per cont, comos ovor as morcury, about same quantity is con verted into "stupp," &c, for furthor treatmont, and is only used for smalls and slime.

2. Non-continuous oven, used at Now Abandon, California: This oven will work 30 to 55 tons, and consists of a fii'o-placo for wood, 3 to 5 foot high, communicating by an opening in a masonry wall, with nn oro chamber 7 foot long, 4 feet broad, 5 feot high; tin's again communicates 8 or 9 con donsing chambors of equal size, built of stone, plastered inside, provided with gutters on tho floor for conducting away tho condensed morcury from tho masonry chambers. The vapours pass into wooden chamberí, in which a continuous shower of

water ia kept up; anti what is then uncondonsed passes away through a wooden chimney. Tho fur nace is kopt going sovon days. To prevent tho morcury soaking into tho ground, tho ovons Btand on douhlo archos of stono, and in theso lio iron plates. "With tho old fashioned oven tho mercury has hoon known to ponctrato tho gound 25 to 30

foot.

j 10. Inox AND WOODEN TUHES.

Experience has shown that iron tubes get worn through in about a year. Wuodon tubes cost less last longor, and afford "stupp" freo from iron ; but on account of their low conducting power, conden sation can only bo oflectcd by tho water percolating inside; this occasions loss by tho water carrying away somo of tho fino froth containing morcury

Globules.

S. Li. JJENSUSAN.

Sydnoy, 24 Deecmbor, 18C9.

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