"Now, the mixture has to be made to give back that gold. First of all it is pressed through canvas or buckskin in order to get rid of the liquid quicksilver, which will pass through the weave of the first and the pores of the second, leaving inside only such of it as has firmly allied itself with the gold to form the amalgam.
"The next thing to do is to put this amalgam into a retort, out of which leads a long pipe, and to subject this retort to intense heat. Quicksilver is vaporized at a comparatively low temperature—for a metal. It is driven from the amalgam in the form of vapor, much as water may be driven off in steam. The quicksilver vapor passes along this long pipe, which leads to several coils placed in a tank of running cold water. The cold chills the vapor, condensing it into the liquid state again, and the quicksilver runs out of the end of the pipe, ready for use once more. The pure gold is left.
"But, even with the use of quicksilver on the sluice there was still 40 per cent. of the gold that got away. For many years there was no practical way of recovering this loss, and the chemists of the world tore their hair in despair. What was needed was to find some other chum of gold, even more affectionate than mercury. The chemists found this new friend, at last, in cyanide, which is a salt of prussic acid. Cyanide, Clem, is an arrant flirt, as I'll show you, in a minute.
"Nowadays, the tailings, after passing over the long sluice or flume, and after having dropped the heavy gold in the riffles and given some of the light gold to the quicksilver, are led to a huge churn. There the earth and water are pounded together into a sort of slime. A wheel lifts this slime into a movable chute from which it is poured into a series of vats or tanks. These tanks contain cyanide, which has already allied itself with a chum—potassium.
"But cyanide likes gold even better than it does potassium, and, as soon as the slime strikes the vat, the cyanide lets go the potassium and clings to the gold. Cyanide of gold is formed. So far, so good. But what the miner wants is pure gold.
"The cyanide is pumped up out of those tanks into another chute, which pours it into a second lot of tanks, fastened to the side of which are large bundles of zinc shavings. The cyanide liked the gold better than the potassium, but it has the bad taste to prefer zinc even to gold. It releases the gold and flies to the embrace of the zinc. The gold, suddenly deserted of the friendship of the cyanide, powders down to the bottom of the tank, in absolutely pure form, ready to be melted down into bars. By other processes, which I won't bother you by describing now, the zinc is released from the cyanide, and the cyanide is led to its old friend the potassium, ready to begin work anew. So, you see, nothing is wasted.
"This process, and this only, has made the astounding wealth of South Africa, for, as I told you, the reefs there are of very low-grade ore, so low that Jim, here, would have turned up his nose at it. The modern ability of chemists to get out the tiniest particle of gold that lies in the most stubborn rock has made the Rand a richer region than a prospector's wildest dream."
"If I'd known all that, forty years ago, I'd be a rich man now," said Jim, regretfully.
"You'd have been a millionaire, ten times over," Owens agreed, "but, since it hadn't been found out, you couldn't have known it. But did you always stick to gold, Jim? That Carson River country has got more silver in it than it has gold."
"Don't I know it? 'Ain't it been rubbed into me, good an' hard? Father wasn't a cussin' man, noways, but he couldn't keep his tongue in order like a man should, when he got to talkin' about silver. He threw away any amount o' high-grade silver ore, while huntin' for gold. The richest silver mine in the whole world, I reckon, was found less'n a hundred yards from where he'd been pannin'.