series of riffles," or obstructions, against which the heavier portion of the material lodges. Quicksilver is fed into the stream at various places in the form of a fine rain, being squeezed through chamois leather or canvas to give it dispersion. It passes down the inclined surface and lodges with the other heavy material against the riffles, where it collects the gold by amalgamation. When the first riffle is full, the material suspended in the water passes over the obstruction and is caught in the next one, and so on till all are filled. The water is allowed to flow until all the earthy matter that the current can carry is disposed of. Then the clean-up" begins. The gold is found amalgamated with the quicksilver.

46

Hydraulic mining is sluicing on a large scale, in which the force of a jet of water is used, instead of shovelling, to break down the bank and move the earth and gravel to the entrance of the sluice. For this purpose a powerful head of water is required, from one hundred to three hundred feet higher than the ground to be operated on. The water is collected in mountains, sometimes at long distances from the works, and brought in ditches which follow the contour of the country, often crossing valleys on high trestle-work or by inverted siphons. Sometimes the pay gravel" is found where there is insufficient drainage, and it becomes necessary to excavate tunnels to carry off the tailings. One such tunnel in California is 7874 feet long. The water is delivered against the bank through an iron nozzle with something like the velocity of a cannon ball. It soon excavates a hole, which is gradually enlarged until the superincumbent mass falls down. Then this is attacked by the same means, and the whole mass begins to dissolve and follow the drainage line which brings it to the sluices constructed like those already described, but on a much larger scale. They are operated on the same principles as the smaller

ones.

The disposition of the tailings has been the most serious problem of hydraulic mining in California. Not only is the natural drainage of the country altered by these operations, but stupendous quantities of earth are carried down and deposited in the beds of the rivers, which are caused to overflow their banks and spread the detritus over the adjoining lands, to the ruin of agriculture. A vast deal of litigation has ensued, and the State Legislature has been compelled to intervene for the protection of the farmers. Hydraulic mining is the most economical of all methods of obtaining gold, the cost being from, I cents to 8 cents per ton of material treated. The most expensive is panning, the cost of which is $5 to $8 per

ton.

Gold existing in rock formation is either free-milling or combined chemically with other substances. Often both are found in the same mine. Free-milling ores are treated by crushing and then amalgamating with quicksilver. In reaching the metal and tearing it from the rock, man accomplishes with his own hands what nature has done for him in the case of placer gold.

There are numerous methods of crushing free-milling ores, the one most largely used being that of the stamp battery. The ore is first reduced to the size of a walnut by a stone-breaker. It is then put into an elongated mortar made of cast-iron which has a series of iron pestles arranged side by side, so as to be lifted, one by one, by a revolving wheel and allowed to fall. Water is supplied to keep the mass in a splashing state, and also quicksilver to amalgamate the gold as it is released from the pulverised rock. Sometimes the sides of the mortar are lined with copper plates, which have been previously amalgamated with quicksilver, as the amalgam produced in the mortar tends to adhere to the surface of such plates. The contents of the mortar are thus reduced to a "pulp," which is allowed to flow slowly over a series of

amalgamated copper plates, by which still more of the gold is amalgamated and retained, the remainder passing off as tailings. The tailings contain some gold, and are subjected to further treatment. The excess of quicksilver in the amalgam is recovered by squeezing it through filter-bags of chamois leather or buckskin, which leaves a solid amalgam. The remainder is evaporated by heat and the vapour condensed by passing through pipes which are submerged in cold water. The solidified gold remains.

There are two important chemical processes for the extraction of gold from sulphides and other refractory ores, one by chlorine, the other by cyanide of potassium. By the former the ore is first reduced to sizes small enough to expose all the gold contained in it to contact with chlorine gas. It is then roasted, either in a reverberatory or a revolving furnace, in order to expel sulphur, arsenic, and other impurities which would impede the action of the chlorine. The charge is then drawn from the furnace and allowed to cool, after which it is shovelled into a vat and impregnated with chlorine gas. Then it is leached with water as wood-ashes are leached for making lye. The resulting liquor contains chloride of gold, which is usually precipitated by adding to it a solution of sulphate of iron, the gold falling to the bottom in the form of a powder, and usually in a very pure state, sometimes as high as 990. Precipitation can be effected also by passing the solution over charcoal, to which the gold adheres, the charcoal being afterwards burned and the gold recovered.

The cyanide process is of comparatively recent date. It has been in operation in the United States less than ten years; in South Africa a little longer. A solution of cyanide of potassium will dissolve metallic gold. This affinity is new the basis of great industries and has enabled mankind to save large quantities of the precious.

metal that would otherwise have been lost. The process is substantially like that of chlorination, except that roasting is not generally required. The ore is first comminuted, as in chlorination, and placed in large vats, where it is leached by a dilute solution of cyanide, the liquor being allowed to remain until all the gold has been extracted. It is then drawn off by a stop-cock into a box under the vat. The gold is precipitated by zinc shavings, and falls to the bottom of the box in the form of a slime. Another method of precipitating the gold is by electrolysis. A current of electricity is passed through the solution, and the gold is precipitated on thin sheets of lead suspended in it and to which it adheres. These are melted in order to recover the gold. More recently sheets of aluminum have been used instead of lead, as the gold can be removed without injury to the sheets. The cyanide process has added largely to the productiveness of the gold-fields of South Africa, and has made the accumulated tailings of past years a source of profit. It has made many mines profitable that could not be worked before.

It was the opinion of Professor Newberry twenty years ago that nine tenths of all the gold in the possession of mankind had been obtained from placer deposits. At the present time, the greater part of the annual increment is obtained from veins in rock formation. The methods of extracting it are endless in number and variety, but all that we need consider here depend upon quicksilver, chlorine gas, or cyanide of potassium, and of these three agents, quicksilver is still the most important.

DEVELOPMENT OF STEEL MANUFACTURE

IN THE UNITED STATES

BY ANDREW CARNEGIE

write of the manufacture of steel in the United

States during the last century is indeed to begin at the beginning, since the Legislature of Pennsylvania, as late as 1786, lent Mr. Humphreys £300 for five years to enable him to try to make bar iron into steel as good as in England." As late as 1810, there were produced in the whole country only 917 tons of steel, Pennsylvania's share being 531 tons, or more than half of the whole. It is remarkable that the good old Keystone State still makes about the same percentage. Even in 1831 the production of steel was only 1600 tons, an amount which was said then to equal the whole quantity imported, so that the market for steel was divided equally with the foreigner seventy years ago. But this steel was made chiefly by cementation; crucible steel was to come later. From 1831 until as late as 1860, very little progress was made in developing the manufacture of steel, for the total product in 1850 was only 6000 tons, still principally blistered steel. In 1840, Isaac Jones and William Coleman began its manufacture in Pittsburgh, and succeeded. Singer, Nimick & Co. in 1853 produced successfully the usual grades of cast steel for saws, machinery, etc.; for kindred purposes Hussey, Wells & Co., in 1850, made the first crucible steel of best quality as a regular product out of American iron, and in 1862 came Park Brothers & Co., with the biggest steel plant of all up

10