# Popular Mechanics/Volume 49/Issue 1/Eight-Cent Gold-Digger Earns Millions

Twenty-Five-Ton Steel Miner That Can Earn Big Profits from Worked-Over Gold Sands That Wouldn't Have Kept a Forty-Niner Supplied with Food; Five Men Operate the Dredge
By H. H. DUNN
Out of the great piles of sand and gravel discarded as worthless by the "Argonauts of Forty-nine," in their search for gold in California's mountains, new millions are being taken every year by a novel mechanical process, which does away with prospecting, makes mining a certainty and puts the yellow metal back as one of the most important products of the state. From ancient and often buried river beds, as well as from the mine dumps and tailings, handling nearly 100.000 tons a day, these great machines, the first of their kind in the world, are wringing wealth for their owners from sand and gravel running as low as eight cents a ton in gold.
These are the lowest-grade gold deposits ever worked by man. The mechanical miners that have reclaimed them are the largest in any branch of the mining industry, yet their operations are as carefully and as delicately carried on as those of any microscopic investigation ever undertaken in a laboratory.
There are six of these machines working the California mountains, digging their own paths, floating on their own rivers, piling up gravel and rock embankments, and searching out every fleck and flake of gold to a depth of more than eighty feet below their flat steel bottoms. More than 200 men are required to operate and keep them in repair; they work night and day, and consume as much electric power every twenty-four hours as a city of 60,000. They are built in the form of dry-land dredges, but they also operate on water.
Sifting a ton of sand and gravel to get eight cents' worth of gold would have been too delicate a task for the fingers of the miner of '49, and the results would not have kept him in beans and bacon, not to mention flour and molasses, since he was not able to "pan" much more than a ton of earth in a week. But the great scoops of the steel miner get it all, at a rate which has produced more than $50,000,000 since the dredges went to work. In that time they have handled approxi- ​mately 135,000,000 cubic yards more of material than were excavated in the cutting of the Panama canal.
Each Scoop Bucket on the Excavating Chain Weighs 4,400 Pounds and Can Descend Over Eighty Feet below the Water
Just as the placer miner of the days of gold in California shoveled the gravel into a crude rocker, poured water over it, and depended on gravity to drop the gold to the bottom, where mercury picked it up, so the dredge, taking a ton where the miner lifted a shovelful, goes through the same process mechanically. Five men, masters of the metal monster, handle more than 15,000 tons of gravel and sand in the twenty-four-hour day. There are, of course, three shifts of five men each in that length of time, but the crew of the dredge is never more than five men at once.
Two permanent channels, each 500 feet wide and nearly three miles long, have been dredged to a depth of more than sixty feet, and two others, which will be of approximately the same length and width, are now being made. The gravel, cleaned of all the gold, is piled in solidly packed walls along these channels, furnishing what the gold diggers' owners claim to be permanent holding walls, between which flood waters and freshets are carried away from the agricultural lands on either side.
All the work so far accomplished has been done on the barren waste of tailings, which accumulated in the days of unrestricted hydraulic mining, when millions of yards of this waste material was dumped annually along the upper reaches of the Yuba river, where the modern mechanical method of mining is being applied.
Each of the six dredges is larger than many a deep-sea steamer, being 165 feet long, 68 feet wide, and weighing approximately 2,500 tons. A set of huge steel scoops, hung on an endless chain running over the "trunk" of the metal mastodon, reaches far down into the pile of gravel or the buried river bed and lifts out the dripping gravel. There are ninety-six of these scoops on the chain of each dredge, and each scoop carries one ton of material, when filled.
As the loaded chain moves sluggishly upward, dumping its content into the ever-open mouth of the mastodon, there follows a tremendous air-shaking medley of sounds, which becomes continuous as the dredge gnaws into the gravel. It is the crunching, groaning, roaring, grinding, clattering of stones from the size of a man's head down to that of a buckshot, all falling on moving metal screens and thence off these onto the shaking tables, until all has been sifted, the stones carried away and the heavier gold dropped through to be left in the grip of a pool of quicksilver.
The average depth to which the scoops go is sixty-two feet, but when a deeper pocket of gravel is found, the mastodon sends its great trunk down as much as ​twenty feet farther—all in search of eight cents' worth of gold. Sand and gravel brought up by the scoops are dumped first into a huge steel hopper at the very top of the superstructure of the dredge. Thence they pass to a screen, which, revolving at a steady pace, separates the fine material from the coarse and discards the latter.
The Miner, with His Pan and Burro Supply Train, Could Handle a Ton of Gravel a Week, Whereas the Steel Miner of Today Extracts Gold from 15,000 Tons a Day
Water under heavy pressure is then automatically sprayed on the gravel and the finer, gold-bearing sand is thus washed through the screen into a distributor, from which it flows in a slow stream over rows of riffles, improvements over the sluice boxes of the hand miner who first worked these "diggings." In these riffles, quicksilver lies in wait to pounce on every grain of gold, so that, when the sand and gravel leave the device, they are free of all values. In the meantime, the coarser gravel, from which the nuggets and flakes of gold had fallen away in the moving screen, is passed onto belt conveyors, which carry it over long arms and pile it at either side or to the rear of the dredge. When the engineer of this mastodon wishes it to move, he shifts a switch, and one or the other of two forty-five-ton steel legs—called "spuds"—languidly extends itself, buries its point fifteen or twenty feet in the river bed or bank, and, like a dancer turning on her toe, the 2,500 tons of dredge swings about. The second "spud" finds a hold, and the great machine either settles down to resume hunting for gold or continues "walking" on its twin steel legs.
It is estimated by engineers and mining ​experts employed by the government of California that natural treasure, beside which that taken by the dredges is trifling, is still lying in the gravel deposits of the state. From 1853 to 1909, it is stated, $1,200,000,000 in gold was produced by hydraulic and placer-mining methods from the river beds, old and new. State engineers believe that there are at least fifty, and probably one hundred, surface and buried-river gravel beds which never have been touched by miners, though their gold content may be too low for profitable working.
Cutting a Channel 500 Feet Wide, the Great Dredges Need Only Enough Water in the Pond to Float Them, For the Water Goes Along as They Move Forward in the Cut
LONGER LIFE FOR RUBBER SEEN IN NEW TREATMENT
Chemists have developed a new treatment for rubber goods, to prolong the life of the material by counteracting the effect of oxygen. Experts declare that some rubber articles would last almost indefinitely were it not for the results of oxidation from the air. Tires, for instance, suffer a serious loss in tread abrasion, owing to this process. Besides offsetting the action of oxygen, the new substance is said to counteract the effect of high temperatures, which is of importance regarding bus and truck tubes, often exposed to heat and air at once.
SANDGLASS EGG TIMER RINGS BELL WHEN DONE
For boiling eggs up to five minutes, a timer operated by a sandglass has been introduced. It can be set for almost any interval under five, and as the sand runs into the lower glass, the weight causes the tube to descend. This releases another weight at the proper time, and a bell rings, announcing that the eggs are done.
GAS TO BE MADE AT THE MINES AND PIPED TO CITIES
Believing that the gas industry is still in its infancy, engineers predict that gas soon will be produced at the coal mines and piped into distribution centers, saving the costly transportation of coal and the erection of large plants on expensive land. The chief problem in the way at the present is a means of successfully transmitting the gas long distances and, when this is solved, it is believed that the gas industry will be able to take over a much larger percentage of the home-heating and cooking tasks than can now be done and that gas will be used much more extensively in manufacturing. Another problem that must be solved is the profitable disposal of by-products. Many of these materials have a limited market at present. How the gas industry is already aiding aviation was shown by the announcement that 1,500 companies are ready to mark their huge storage tanks with insignia that will help guide pilots. New England states reported that the number of installations of home-heating plants using gas had increased from 1,308 to 2,600 in a year.
DANCE HALL LIKE MONOPLANE LATEST RESORT NOVELTY
Closely resembling a huge monoplane on the exterior, a dining room and dance hall in Fort Worth, Tex., has attracted considerable attention. It is sixty feet long, twenty feet wide and accommodates a fairly large crowd with comfort.
It Doesn't Fly but Dancers Enjoy It: the "Airplane" Hall near Fort Worth, Tex., for Dining and Dancing
TALKING MIRRORS HELP DEAF IN LEARNING SPEECH
Correcting His Own Lip Movements with Aid of the Mirror: Deaf Child Learning Speech
So that deaf children may more easily learn how to place their lips in correct position for pronouncing syllables, use is made of mirrors in a school at Atlanta, Ga. The pupils strive to imitate their teacher and with the aid of the reflectors, can correct their own errors.
SKIN REGISTERS EMOTIONS
Recent experiments by David Wechsler, a New York psychologist, have further shown that the skin is an emotional barometer, so that the familiar description of "thick-skinned" and "thin-skinned" persons has some basis in fact. However, the difference in behavior depends not so much on the question of relative thickness as on the electric resistance of the skin. Of all tissues, the skin is one of the best insulators and, like other materials, it offers less resistance to electricity when moist. Under various emotional strains, perspiration is induced, and the consequent increase in moistness results in greater conductivity of current. Practical use of this discovery has been suggested in the field of criminal investigations.
SIGHT-SEEING BUS AT THE ZOO SERVES SMALL BOYS
German Boys in the Special Car That Takes Them around the Zoo in Hamburg for Two Cents Apiece
For the equivalent of two cents in American money, small boys may enjoy practically all the wonders of the zoo in Hamburg even if the pens and cages are partly obscured by taller adults, for an elevated sight-seeing bus takes them all about the grounds. It holds thirteen passengers.
WHALES TAGGED WITH DARTS TO TRACE TRAVELS
Shooting silverplated darts into hundreds of whales, each dart being marked with the date and longitude and latitude, a party of British scientists have recently completed the first organized attempt to solve the life story of the big sea mammals. They spent two years in the antarctic seas, sailing in the famous old ship "Discovery," which was used by both Scott and Shackleton on their explorations of the southern ice continent. The expedition was directed by the government of the British colony in the Falkland islands, center of the whale-fishing industry of late years. The whalers have been asked to return the darts, with the date and place where the whale was killed, in order that the age and migration of the big fish may be checked. The scientists hope to solve the riddle of the whale's family life, the number of his wives, and the length of his life. Although many whalers have claimed that the whales mated but once, the evidence gathered indicates that the whales really are polygamous. Besides studying the whales, they collected marine life in the southern seas to a depth of three miles. The "Discovery" was specially built for exploration in the ice pack, with planking two feet thick backed by massive cross braces to resist tons of pressure, and fitted up for scientific research.
JEWELS THAT AIDED COLUMBUS VALUED AT HALF MILLION
The jewels that Queen Isabella of Spain pawned to raise money for financing Columbus and his voyage to America are valued at approximately $500,000, although they are worth many times that from the viewpoint of their historical interest. The set consists of 280 stones weighing 500 carats, and the largest diamond weighs fifty-four carats.
Some of the Jewels That Helped Columbus Reach America; Part of Queen Isabella's Diamond Collection
"SEA FLEA" FOR OCEAN FLIGHT DEVELOPS HIGH SPEED
It Won't Sink If It Lands on Water: the "Sea Flea" for Transatlantic Flights
Half plane and half boat, an odd-looking craft, called the "Sea Flea," has been constructed for a flight across the Atlantic. It is designed to skim close to the surface of the water and forced landings will present no hazard, as the rig is constructed to float indefinitely. A speed of seventy-five miles an hour can be reached, it is claimed. On a test the flea crossed from France to England, a distance of twenty-one miles, in twenty-six minutes carrying three persons and the pilot.
SUPERSPEED PHOTOS OF TIRES TO REVEAL FAULTS
Thirty-two hundred pictures a second! That is the performance of a superspeed camera C. Francis Jenkins has developed for taking photographs of rubber tires while they are in actual service, so that engineers can determine where the strain and stress are distributed when traveling at high speed under varying conditions, The camera differs in many respects from the usual motion-picture instrument. Instead of one, it has forty-eight matched lenses and the film moves continuously at the rate of 200 feet a second. The lenses are set in a disk which is rotated by an electric motor.
STRIPING AUTOS MADE EASY WITH PENCIL PAINTER
Applying the paint stripes to the automobile is usually left to experts because of the accuracy required. But with a striping pencil now on the market, a novice can perform the task without difficulty. The instrument is fitted with a specially designed base, which can easily be guided in a straight line by the car molding. A brass tube, containing paint, constitutes the pencil. It has a rubber bulb at one end for filling and distributing point at the other from which the lacquer flows by gravity. Interchangeable barrels are provided for making stripes of different width.