Last Updated: 11th Dec 2008
Placer Gold Recovery Methods In Early California
Part II: The Rocker Box
by Daniel E Russell
Part II: The Rocker Box
by Daniel E Russell
The Rocker Box
Also known simply as a “rocker,” “cradle” or “cradle box,” the rocker box offered a distinct improvement on through-put of paydirt compared to panning, but required two people to achieve the device’s maximum efficiency. The rocker box very much resembled the old-time rocking cradle for infants, a commonplace object in any home in the 19th Century (and considerably earlier). The rocker box was especially useful in localities where limited water flow prevented the use of sluices and other techniques.
In addition to its use in small-scale placer mining operations, the rocker box found fairly extensive application in sampling gold prospects.
The rocker box was not constructed to one fixed design. Fundamentally, it consisted of a wooden trough, measuring about 20 by 40 inches, and about 4 inches tall. The front end of the trough is open. A series of parallel 1-inch square wooden sticks called “riffles” were attached to the inside bottom of the trough. The description of the earliest rocker boxes the author has read usually state that two riffles were used… one about midpoint of the trough, the other at the “tail” or open end where the water poured out. Over time, it appears that the number of riffles increased.
Atop this sat a “hopper,” or “screen box” a wooden frame with a very coarse screen made from sheet iron – preferably galvanized with zinc - perforated with holes roughly a quarter inch in diameter or “riddle”. The hopper was the same width at the bottom trough of the rocker, but only about half as long. It was not physically connect to the trough below, allowing it to be easily removed and emptied of waste gravel. Invariably a section of canvas cloth (canvas was commonly called “duck” in the 19th century) or carpet was tacked at an angle beneath the hopper, intended to trap as much of the fine gold as possible. This was commonly called “the apron”.
Gardner and Johnson (1934) took measurements of rocker box being used at Greaterville, Arizona. It was “3 feet 4 inches long and 1 foot 9 inches wide on the inside and had a slope of 5 inches. The screen box was 6 inches deep and 20 inches square inside and had a bottom of sheet iron with 1/4- to 1/2- inch holes punched about 2 inches apart. The baffle was 28 inches long and consisted of a piece of canvas. A single riffle 3/4 inch high was used at the end of the rocker.
On the underside of the main trough were two solid wood rockers that allowed the box to be rocked from side to side. As a matter of convenience, most rocker boxes were fitted with a tall wooden handle which the miner grasped to rock the unit from side to side from either a sitting or standing position. Overly-vigorous rocking had to be avoided, as it would increase the amount of fine gold particles lost out through the tail.
In use, the rocker box would be positioned with the two rockers sitting upon boards lain flat upon the ground. The open front or “tail” of the trough needed to be a few inches lower than the back, in order for water to drain completely and carry off the lighter fraction of minerals. A quantity of paydirt was shoveled into the hopper. Using a ladle (often called a “tin dipper” in period accounts) water was poured over the paydirt while the rocker box was rocked back and forth. The larger diameter rock – gravel and cobbles – stayed in the hopper, screened out by the perforated iron sheet but washed by the water to free any adhering gold particles. The agitation created by rocking the box assisted in carrying the lighter fraction sand – quartz, feldspar, mica and the like – over the lip created by the riffle bar at the tail. The heavy fraction, consisting of black sand and hopefully gold, would be trapped by the riffle bar. The trapped material would be lifted out with a spoon made of dark cowhorn (black horn making it easier to see any flecks of gold). The hopper would be lifted out of the rocker box’s trough, and emptied of the barren gravel and larger stones, then replaced to receive the next batch of paydirt. Every few hours, the rocker box was “cleaned up” to remove the gold and black sand caught by the cloth and the riffles. After hand-picking any nuggets of size, the black sand with any fine gold was panned to remove the precious metal content.
The rocker box was simple to construct, was only slightly less portable than the gold pan, required little effort to set-up on a placer site, and was capable of a higher daily through-put than panning. It was, however, labor-intensive, and optimally required two men to operate it (one to shovel and carry paydirt to the rocker box, the other to actually wash and rock the paydirt).
“Upon reaching the bar, a curious scene presented itself. About one hundred men, in miner's costume, were at work, performing the various portions of the labour necessary in digging the earth and working a rocking machine. The apparatus then used upon the Yuba River, and which has always been the favourite assistant of the gold-digger, was the common rocker or cradle, constructed in the simplest manner. It consists of nothing more than a wooden box or hollowed log, two sides and one end of which are closed, while the other end is left open. At the end which is closed, and called the " mouth" of the machine, a sieve, usually made of a plate of sheet iron, or a piece of raw hide, perforated with holes about half an inch in diameter, is rested upon the sides. A number of "bars" or "rifflers," which are little pieces of board from one to two inches in height, are nailed to the bottom, and extend laterally across it. Of these, there are three or four in the machine, and one in the " tail," as it is called, i.e. the end where the dirt is washed out. This, with a pair of rockers, like those of a child's cradle, and a handle to rock it with, complete the description of the machine, which being placed with the rockers upon two logs, and the "mouth" elevated at a slight angle above the tail, is ready for operation.
Modified and improved as this may be, and as in fact it already has been, so long as manual labour is employed for washing gold, the " cradle" is the best agent to use for that purpose. The manner of procuring and washing the golden earth was this: The loose stones and surface earth being removed from any portion of the bar, a hole from four to six feet square was opened, and the dirt extracted therefrom was thrown upon a raw hide placed at the side of the machine. One man shovelled the dirt into the sieve, another dipped up water and threw it on, and a third rocked the "cradle.” The earth thrown upon the sieve is washed through with the water, while the stones and gravel are retained and thrown off. The continued motion of the machine, and the constant stream of water pouring through it, washes the earth over the various bars or rifflers to the " tail," where it runs out, while the gold, being of greater specific gravity, sinks to the bottom, and is prevented from escaping by the rimers. When a certain amount of earth has been thus washed, (usually about sixty pans full are called " a washing,") the gold, mixed with a heavy black sand, which is always found mingled with gold in California, is taken out and washed in a tin pan, until nearly all the sand is washed away. It is then put into a cup, or pan, and when the day's labour is over, is dried before the fire, and the sand remaining carefully blown out. (Buffum, 1850)
“When the rocker is to be used, it is placed in the spot to which the pay-dirt, and a constant supply of water, can most conveniently be brought. The lower end of the cradle is placed so as to be about two inches lower than the upper end. The miner fills his hopper with pay-dirt, sits down by the side of his cradle, pours a dipperful of water upon the dirt, and begins to rock, and keeps on pouring water and rocking until nothing remains in the hopper save clean stones. He then rises, lifts up his hopper, throws out the stones, and is ready to repeat the operation.” (Hittell, 1860)
“An improvement upon the pan was the rocker, a box arranged so that it could be rocked like a cradle, with no board at one end, with a few slats nailed across the bottom to catch the gold, and having a piece of sheet iron on the top pierced with holes a quarter of an inch in diameter. Earth was thrown upon this iron, and water was poured on. The cradle was set upon a slight incline, so that the stones rolled off at the end, while the water, with the earth, sand, and gold, was carried through. The gold caught upon the rifiles, while the lighter substances were washed away. Nuggets, or large pieces of gold that would not pass through the holes, were sometimes thrown out with the stone and lost; but the danger of such an occurrence was not very great, principally for the reason that nuggets were not alarmingly abundant. Two men were required to work a rocker. It was placed by the side of a stream, and one man grasping its handle with one hand, flourished a dipper in the other. His companion brought the auriferous earth to the machine, and threw it upon the iron. Man number one would then throw a quantity of water upon the earth, and agitate the machine as rapidly as possible. The earth and water would become mixed, and pass through the holes, and the stone would roll away from the end of the cradle. It was necessary to keep the water running pretty briskly on the top of the machine, and likewise to keep it well supplied with earth. By the end of the day's working at this business, the two men would be delightfully wearied and ready to engage in almost any other honorable and profitable pursuit, especially a profitable one.
My first experience with a rocker was not of an agreeable character. Accompanied by a friend, I went to a locality where it was reported that a miner a few days before had obtained eight hundred dollars in a single day. We were willing to begin at that rate, though we were confident we should make a thousand a day before the end of the week. We carried our tools to the spot, and having placed our rocker, began work. I worked the machine, and Harry, as I will call my friend, supplied it with earth. I placed the machine by the side of the stream where I could easily dip out the water, and told Harry to begin. For about an hour the machine did very lively work. Whenever I lagged, Harry would remind me of the eight hundred dollar man. Then I would give an extra flourish to the tin dipper, and pile on an extra quart of water. I kept Harry busy bringing earth, and he kept me busy washing it away. At the end of an hour or so we thought we would see how things were getting on. I raised the lid, examined the riffles, and not a particle of gold was to be seen. The result was not encouraging, and I told Harry we had better move a little way down the stream, and try it again. We did so. This time Harry took the rocker, and I went into the shovelling business. We made things lively for another hour. Harry was sure we were right this time, as the earth was of a different color, and the water, as it ran from the machine, was so yellow, that it certainly must be tinged with gold. What we most feared was to lose the big nuggets that might roll out from the rocker, and so we examined every stone…” (Knox, 1876)
“A rocker is simply a box about three feet long and two feet wide, the interior fitted with a sheet-iron division punched full of quarter-inch holes, so placed as to make the first division very shallow. The lower part is fitted with an inclined shelf about eight inches lower at one end than at the other. Over this is laid a heavy woolen blanket. The whole is placed on two rockers much resembling the rockers on an old-fashioned cradle. This arrangement is set up on two lengths of wood convenient to the water supply. Having put some pay-dirt in, with one hand the miner rocks the cradle, and with the other he pours in water. The finer matter with gold falls through to the blanket, which holds the fine particles of gold, while the coarser particles of dirt are washed on and out of the box, which usually has some mercury on the thin slats over which the refuse runs to catch any gold that may have escaped the blanket. Of course, any large nuggets will be held on the iron division. At intervals the blanket is taken out and washed in a barrel of water containing mercury.” (Haskell, 1898)
Buffum, E. Gould
Six Months In The Gold Mines From A Journal Of Three Years' Residence In Upper And Lower California, In 1847-8-9.
Metallurgy of Silver, Gold and Mercury in the United States
New York 1890
Gardner, E D and Johnson C H
"Placer Mining in the Western United States"
US Bureau of Mines Information Circular 6786 Sept 1934
Haskell, William B.
Two Years In The Klondike And Alaskan Gold-Fields
William B. Haskell
Hittell, John S.
Mining In The Pacific Sates of North America
New York, 1862
Knox, Thomas W.
Underground, Or A Life Below The Surface
Hartford CT 1876
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Locality Updated: Marinha Grande, Leiria District, PortugalFrom Rui Nunes, 26th Nov 2014 12:45:23