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for five or six (5 or 6) hours, the cloth is converted into a tinder and afterwards scraped off the cullender by a brass brush.
In 1790 the "Freiberg,” or “ Barrel process,” of amalgamation was introduced at Halsbrücke, near Freiberg, in Germany. The ore contained, beside the silver, antimony, arsenic, copper, lead, iron, and zinc, and sometimes gold, bismuth, nickel and cobalt; in small quantities the silver varied all the way from 15 to 200 ounces per ton, these were mixed to make an average of 75 to 80 ounces per ton; latterly the rich and poor were kept separate, as it was found to be more economical to do so. It was required at least that 25 per cent. of iron pyrites be contained in
If the amount contained in the ore was less than this, addition was made either of pyrites or sulphate of iron, when the pyrites or other sulphides were in excess, the roasting was resorted to to get rid of it, as in the other processes. The ore was roasted in a state of fine division with salt, the oxidation of the pyrites causing the evolution of chlorine and hydrochloric gases, which coming in contact with silver sulphides and other salts of that metal, converts them into chloride; the ore was ultimately amalgamated in revolving barrels; a minute description of this process may be found in any of the standard works on metallurgy. This process was abandoned at Halsbrücke, in 1856, on account of its expensiveness and its unsatisfactory results when applied to certain classes of ore. Over half a century had changed the relationship existing between the prices of labour and fuel ; so that it was found to be advantageous to give up the amalgamation process and smelt the ores with others containing lead. This process has also been in use to a certain extent in the United States and also in Mexico. The amalgamation process employed at the Mansfield Copper Works to obtain the silver contained in copper matter was similar to this, but has since been abandoned for Ziervogel's process.
In 1859 the Washoe or Pan process was invented to treat successfully the ores of the great Comstock lode, situated at Virginia City in the Washoe District, State of Nevada. It received the name “Washoe" from its first being introduced in this district. It really owed its invention to the failure of both the Barrel and Patio processes, as both from metallurgical and climatological conditions these processes were unsuited for and proved a failure in the attempts made to apply them to the ore, which contained from $30 to $150 per ton of 2,000 lbs., besides zinc blende, galena, argentite, iron and copper pyrites, and sometimes stephanite and polybasite. The gold occurring to the amount of one-third of the total value of the ore, one portion of the ore only could be treated by the Barrel amalgamation process, and this was that 'portion which assayed above $150 per ton ; all the rest of the ore below this being treated by the Washoe process. In this process the ore is ground wet in stamp mills; after having been reduced to a suitable size for seeding, the ore passes off in suspension in water through sheet-iron screens and is collected in reservoirs from which it is removed to the pans to be ground with mercury and hot water, with or without the addition of cupric sulphate and common salt-the amount of this used varying in different works but generally consisting of from one to three pounds—to each charge of ore which consists in the old pans- those of Varney, Wheeler, Hepburn and Peterson-of 1,200 to 15,000 lbs. of ore, but in the later and larger pans—those, for instance of McCone and Mountain —the charge is 4,000 to 5,000 lbs. The description of this process and the machinery employed in it have been so voluminously treated of that it would be superfluous for me to again describe it. Suffice it to say that the benefit of the “chemicals” is doubted by some and the real action of them is not understood. As far as the conducting of the live steam into the pulp is concerned, either loose or in the shallow chamber, it appears to me that its principal effect and value is that it keeps to a certain extent the mercury from flouring. The Boss continuous process, patented by Mr. Boss of United States, is a modification of this process, in which a series of pans are employed, into which the pulp passes, instead of it passing directly into the separators.
Although amalgamation of gold ores was effected in the streaming mills, arrastras and Chilian mills for centuries, it was not until this century that amalgamation was effected in the batteries of stamp mills, and at the present time the greatest portion of the gold ores are treated in this way, amalgamation being cffected by the mercury added and the amalgamated copper plates fixed to the inside of the mortar boxes or caught on the amalgamated apron riffles of the sluices. A great many contrivances have been invented for the tailings besides the amalgamated rifles ; blankets, sluices were used, and also various jiggers, buddles, vanners, etc., for concentrating these tailings, which are afterwards treated in such machines as the Attwood amalgamator, the Eureka rubber pans, the Hungarian mill (which was used at Chemnitz and other localities), and various other inventions. Stamps themselves date far back as grinding inills, though not so as amalgamators. Various mills of late years have been invented as direct amalgamators, notable among which is the Crawford mill. This mill consists of a pan or basin of cast iron supported on four iron uprights, which are attached at the bottom to a circular iron frame which forms the base. The bottom of the pan or basin is elevated at its centre and gradually slopes to the sides; a little over half-way to the sides the bottom suddenly is depressed, thus forming an annular groove round the outer edge of the bottom of the basin. Through the centre of the bottom of the pan or basin, where there is an opening, a short upright piece of shafting passes, which fits at the bottom into a journal in the centre of the base. After passing through the opening in the bottom of pan, it is attached at its top extremity to a false bottom, which fits upon the true bottom, almost completely covering the above-mentioned groove, leaving only a small space open communicating with the upper part. The sides of this false bottom, as also the sides of the pan at the same level, have steel castings attached to them. On the area formed by the steel castings, which form also a groove which forms a half circle and a complete ring round the pan, balls of iron are placed which revolve when the false bottom, which is attached to the upright shaft, is set in motion by gearing attached to the shaft between the bottom of pan and base of stand; over the pan is bolted a dome, which at its apex continues perpendicular to form a pipe, round which near its top is a circular stage with a spout; inside this “pipe" fits a second, whose mouth is expanded to a filler; the bottom extends down further than the commencement of the apex of the dome to almost the level of the tops of the balls; this acts as the hopper through which the ore is fed. To the bottom, at one side of the first-mentioned annular groove, is attached a mercury pipe, through which the mercury is fed to the mill; a water pipe enters at that part of the centre of the bottom where the upright shast, bearing the gearing for driving, enters; an oil supply pipe also supplies oil to the bearing of the shaft as it enters the bottom of pan.
The ore is fed by the hopper and is ground by the circular motion of bottom and balls to one hundred to two hundred (100 to 200) mesh. The first-mentioned annular groove, is filled with mercury, into which the finely divided gold gravitates through the water; the matrix and other minerals being finely divided and having a less specific gravity than gold are forced up and carried off by the water, the water passing off by the opening formed by the pipe of the hopper and the continuation pipe of the dome, it rises through this space, falls over on the circular stage and flows away by the spout; the water enters with a considerable upward pressure, which keeps everything but the gold from reaching the mercury, this pressure is exhausted by the lateral sweep of the balls and expansion in the wide dome. The mill is claimed to be able to treat any and every ore of gold, arsenical, pyritical, antimonial or the most refractory ore and save over (90%) ninety per cent., requiring less power than “ stamps," and one-fourth (14) less water, and one very good thing about it, I think, is that the tube by which the amalgam is drawn off is securely padlocked, thus preventing the stealing of amalgam, which, as we are all too well aware, has been practised too often in the past.
Thus the amalgamation process stands to-day the result of development from the old “streaming for gold” mill to the stamp mills, and mills of Crawford type ; from the process of Vanoccio Biringuccio to the Patio, Barrel or Freiberg, and Pan or Washoe process. The use of chemicals seems to have received a fair share of consideration, although we are a little startled by the statement made in an anonymous Latin account of amalgamation similar to the Patio in which ground horns, bricks, and sulphur are added to the usual complement of chemicals, and said to have been practised in Guatemala by the writer; the sulphur astonishes us when we know the dire results of its coming in contact with either the gold or mercury in the amalgamation process. The applications in November, 1864, by Dr. Wurtz, of New York, and in February, 1865, by Mr. Crookes, F.R.S., of London, for the patent for the use of sodium amalgam in the amalgamation process, Wurtz for America, and Crookes for Britain, revealed the fact that both had been experimenting on the same principle for the benefit of science without the knowledge of the other. This is at least one point of general interest in the amalgamation process; but although extensively tried both in California and Australia, the results obtained differed greatly, and it was not used as much as had been expected, although up to the present it has its partisans, and to a certain extent, it had a beneficial influence. I have noticed that mill men prefer mercury that has been formerly used which is known to contain gold or silver amalgam, as it is supposed to be more effective in absorbing the metals than the clean mercury. The amalgamation process, according to some, has reached its zenith ; whether this is so or not is hard to say, whether more brilliant inventions and discoveries will be made in the application of the amalgamation process remains to be seen. Tiine alone will tell. One thing is apparent to all, namely, that other chemical processes are gradually gaining ground and recognition, although our dear old friend is hoiding the ground bravely, and it may be said in conclusion that it can look back at its past and honorable history, as a nobleman looks back over his long line of descent, and may treat with scorn the upstart claimants of a day for the honorable position of the Amalgamation Process in Metallurgy.
NOTE. A number of attempts have been made to apply electricity in the amalgamation process by means of sending electric currents through amalgamated rifles, terraces and aprons; noticeable among others was the machine invented by one Charles M. Dobson in 1887, in Toronto, considerable notice of which was taken and a full description given by the journals of that date. The electricity was applied in this machine by means of a carbon shod diaphragm, which moved backwards or forwards over the surface of amalgamated copper plates, the electricity being supplied by a small dynamo. The advantages claimed for this invention were that the electricity as conducted by the carbon shoes kept the surface of the mercury clean and bright, volatilizing any sulphur or arsenic which came in contact with it and agitating any other metallic constituent present, thus keeping them from coming in contact with the mercury and allowing the gold and silver the full benefit of the pure mercury. No further comment is required on this subject, further than that these inventions enjoyed existence for a very short time.