Roughing It

by Mark Twain

Chapter XXXVI - A Quartz Mill - Amalgamation

A Quartz Mill—Amalgamation—“Screening Tailings”—First Quartz Mill in Nevada—Fire Assay—A Smart Assayer—I stake for an advance

I had already learned how hard and long and dismal a task it is to burrow down into the bowels of the earth and get out the coveted ore; and now I learned that the burrowing was only half the work; and that to get the silver out of the ore was the dreary and laborious other half of it. We had to turn out at six in the morning and keep at it till dark. This mill was a six-stamp affair, driven by steam. Six tall, upright rods of iron, as large as a man's ankle, and heavily shod with a mass of iron and steel at their lower ends, were framed together like a gate, and these rose and fell, one after the other, in a ponderous dance, in an iron box called a “battery.” Each of these rods or stamps weighed six hundred pounds. One of us stood by the battery all day long, breaking up masses of silver-bearing rock with a sledge and shoveling it into the battery. The ceaseless dance of the stamps pulverized the rock to powder, and a stream of water that trickled into the battery turned it to a creamy paste. The minutest particles were driven through a fine wire screen which fitted close around the battery, and were washed into great tubs warmed by super-heated steam—amalgamating pans, they are called. The mass of pulp in the pans was kept constantly stirred up by revolving “mullers.” A quantity of quicksilver was kept always in the battery, and this seized some of the liberated gold and silver particles and held on to them; quicksilver was shaken in a fine shower into the pans, also, about every half hour, through a buckskin sack. Quantities of coarse salt and sulphate of copper were added, from time to time to assist the amalgamation by destroying base metals which coated the gold and silver and would not let it unite with the quicksilver.

All these tiresome things we had to attend to constantly. Streams of dirty water flowed always from the pans and were carried off in broad wooden troughs to the ravine. One would not suppose that atoms of gold and silver would float on top of six inches of water, but they did; and in order to catch them, coarse blankets were laid in the troughs, and little obstructing “riffles” charged with quicksilver were placed here and there across the troughs also. These riffles had to be cleaned and the blankets washed out every evening, to get their precious accumulations—and after all this eternity of trouble one third of the silver and gold in a ton of rock would find its way to the end of the troughs in the ravine at last and have to be worked over again some day. There is nothing so aggravating as silver milling. There never was any idle time in that mill. There was always something to do. It is a pity that Adam could not have gone straight out of Eden into a quartz mill, in order to understand the full force of his doom to “earn his bread by the sweat of his brow.” Every now and then, during the day, we had to scoop some pulp out of the pans, and tediously “wash” it in a horn spoon—wash it little by little over the edge till at last nothing was left but some little dull globules of quicksilver in the bottom. If they were soft and yielding, the pan needed some salt or some sulphate of copper or some other chemical rubbish to assist digestion; if they were crisp to the touch and would retain a dint, they were freighted with all the silver and gold they could seize and hold, and consequently the pan needed a fresh charge of quicksilver. When there was nothing else to do, one could always “screen tailings.” That is to say, he could shovel up the dried sand that had washed down to the ravine through the troughs and dash it against an upright wire screen to free it from pebbles and prepare it for working over.

The process of amalgamation differed in the various mills, and this included changes in style of pans and other machinery, and a great diversity of opinion existed as to the best in use, but none of the methods employed, involved the principle of milling ore without “screening the tailings.” Of all recreations in the world, screening tailings on a hot day, with a long-handled shovel, is the most undesirable.

At the end of the week the machinery was stopped and we “cleaned up.” That is to say, we got the pulp out of the pans and batteries, and washed the mud patiently away till nothing was left but the long accumulating mass of quicksilver, with its imprisoned treasures. This we made into heavy, compact snow-balls, and piled them up in a bright, luxurious heap for inspection. Making these snow-balls cost me a fine gold ring—that and ignorance together; for the quicksilver invaded the ring with the same facility with which water saturates a sponge—separated its particles and the ring crumbled to pieces.

We put our pile of quicksilver balls into an iron retort that had a pipe leading from it to a pail of water, and then applied a roasting heat. The quicksilver turned to vapor, escaped through the pipe into the pail, and the water turned it into good wholesome quicksilver again. Quicksilver is very costly, and they never waste it. On opening the retort, there was our week's work—a lump of pure white, frosty looking silver, twice as large as a man's head. Perhaps a fifth of the mass was gold, but the color of it did not show—would not have shown if two thirds of it had been gold. We melted it up and made a solid brick of it by pouring it into an iron brick-mould.

By such a tedious and laborious process were silver bricks obtained. This mill was but one of many others in operation at the time. The first one in Nevada was built at Egan Canyon and was a small insignificant affair and compared most unfavorably with some of the immense establishments afterwards located at Virginia City and elsewhere.

From our bricks a little corner was chipped off for the “fire-assay”—a method used to determine the proportions of gold, silver and base metals in the mass. This is an interesting process. The chip is hammered out as thin as paper and weighed on scales so fine and sensitive that if you weigh a two-inch scrap of paper on them and then write your name on the paper with a course, soft pencil and weigh it again, the scales will take marked notice of the addition.

Then a little lead (also weighed) is rolled up with the flake of silver and the two are melted at a great heat in a small vessel called a cupel, made by compressing bone ashes into a cup-shape in a steel mold. The base metals oxydize and are absorbed with the lead into the pores of the cupel. A button or globule of perfectly pure gold and silver is left behind, and by weighing it and noting the loss, the assayer knows the proportion of base metal the brick contains. He has to separate the gold from the silver now. The button is hammered out flat and thin, put in the furnace and kept some time at a red heat; after cooling it off it is rolled up like a quill and heated in a glass vessel containing nitric acid; the acid dissolves the silver and leaves the gold pure and ready to be weighed on its own merits. Then salt water is poured into the vessel containing the dissolved silver and the silver returns to palpable form again and sinks to the bottom. Nothing now remains but to weigh it; then the proportions of the several metals contained in the brick are known, and the assayer stamps the value of the brick upon its surface.

The sagacious reader will know now, without being told, that the speculative miner, in getting a “fire-assay” made of a piece of rock from his mine (to help him sell the same), was not in the habit of picking out the least valuable fragment of rock on his dump-pile, but quite the contrary. I have seen men hunt over a pile of nearly worthless quartz for an hour, and at last find a little piece as large as a filbert, which was rich in gold and silver—and this was reserved for a fire-assay! Of course the fire-assay would demonstrate that a ton of such rock would yield hundreds of dollars—and on such assays many an utterly worthless mine was sold.

Assaying was a good business, and so some men engaged in it, occasionally, who were not strictly scientific and capable. One assayer got such rich results out of all specimens brought to him that in time he acquired almost a monopoly of the business. But like all men who achieve success, he became an object of envy and suspicion. The other assayers entered into a conspiracy against him, and let some prominent citizens into the secret in order to show that they meant fairly. Then they broke a little fragment off a carpenter's grindstone and got a stranger to take it to the popular scientist and get it assayed. In the course of an hour the result came—whereby it appeared that a ton of that rock would yield $1,184.40 in silver and $366.36 in gold!

Due publication of the whole matter was made in the paper, and the popular assayer left town “between two days.”

I will remark, in passing, that I only remained in the milling business one week. I told my employer I could not stay longer without an advance in my wages; that I liked quartz milling, indeed was infatuated with it; that I had never before grown so tenderly attached to an occupation in so short a time; that nothing, it seemed to me, gave such scope to intellectual activity as feeding a battery and screening tailings, and nothing so stimulated the moral attributes as retorting bullion and washing blankets—still, I felt constrained to ask an increase of salary. He said he was paying me ten dollars a week, and thought it a good round sum. How much did I want?

I said about four hundred thousand dollars a month, and board, was about all I could reasonably ask, considering the hard times.

I was ordered off the premises! And yet, when I look back to those days and call to mind the exceeding hardness of the labor I performed in that mill, I only regret that I did not ask him seven hundred thousand.

Shortly after this I began to grow crazy, along with the rest of the population, about the mysterious and wonderful “cement mine,” and to make preparations to take advantage of any opportunity that might offer to go and help hunt for it.