and well finished as pressed brick, but they are exceedingly useful.
They need as much care in making as any others, and they must be
burned in a much hotter fire to make them dense and hard. The tests
for paving-bricks are quite different from those for ordinary
building-brick. If first-class paving-bricks weighing fifty pounds are
soaked in water for twenty hours, they take up so little water that
they will not weigh more than fifty-one or fifty-one and a half pounds
when taken out. To find out how hard they are, the bricks are weighed
and shaken about with foundry shot for a number of hours. Then they
are weighed again to see how much of their material has been rubbed
off. A third test is to put one brick on edge into a crushing machine
to see how much pressure it will stand. Paving-brick is cheaper than
granite blocks, and if it has a good foundation of concrete covered
with sand, it will last about three fourths as long. Brick is less
noisy than stone and is easier to clean.
Not so very long ago, when particularly handsome bricks were needed
for the outside of walls and other places where they would be
conspicuous, they were "re-pressed"; that is, they were made by hand
or in a "soft-mud" machine, and then, after drying for a while, were
put into a re-pressing machine to give them a smooth finish. These
machines are still used, but they are hardly necessary, for the
"dry-clay" brick machine will turn out a smooth brick in one
operation.
Another substance which is made of almost the same materials as brick
is terra cotta. To make this, fire brick, bits of pottery, partly
burned clay, and fine white sand are ground to a powder and mixed very
thoroughly. This mixture is moulded, dried, and burned. Until
recently, all terra cotta was of the color that is called by that
name, but now it is made in gray, white, and bronze as well.
Bricks are laid in mortar, and this makes a wall one solid mass and
stronger than it could be without any cement. But mortar does more
than this. It is more elastic than brick, and therefore, when a wall
settles, the mortar yields a little, and this often prevents the
bricks from cracking. Bricks are always thirsty, and if one is laid in
mortar, it will suck the moisture out of it almost as a sponge will
suck up water. The mortar thus has no chance to set, and so is not
strong as it should be. That is why the bricklayer wets his bricks,
especially in summer, before he puts them in place. Lime or cement
mortar will not set in freezing weather, and a brick building put up
in the winter is in danger of tumbling down when the warm days of
spring arrive.
This thirstiness of bricks is their greatest fault. Three or four days
of driving rain will sometimes wet through a brick wall two feet
thick, crumbling the plaster and spoiling the wallpaper. That is why
it is a poor plan to plaster directly on the brick wall of a house.
"Furring" strips, as they are called, or narrow strips of wood, should
be fastened on first and the laths nailed to these, or the wall can be
painted or oiled on the outside. The best way, however, though more
expensive, is to build the wall double. Then there is air between the
two thicknesses of brick. Air is a poor conductor of heat; so in
summer it keeps the heat out, and in winter it keeps it in.
But brick will suck up water from the ground as well as from a storm;
and therefore, when a brick house is to be built in a wet place, there
ought to be a three-eighths-inch layer of something waterproof, like
asphalt and coal tar, put on top of one of the layers of brickwork to
prevent the moisture from creeping up.
Bricks have their faults, but they will not burn, and when properly
used, they make a most comfortable and enduring house.
V
AT THE GOLD DIGGINGS
When gold was first discovered in California, in 1848, people from all
over the world made a frantic rush to get there, every one of them
hoping that he would be lucky enough to make his fortune, and fearing
lest the precious metal should be gone before he could even begin to
dig. The gold that these men gathered came from what were called
"placers"; that is, masses of gravel and sand along the beds of
mountain streams. Each miner had a pan of tin or iron, which he filled
half-full of the gravel, or "pay dirt," as the miners called it. Then,
holding it under water, he shook off the stones and mud over the side
of the pan, leaving grains of gold mixed with black sand at the
bottom. This black sand was iron, and after a while the miners removed
it with a magnet, dried what remained, and blew away the dust, leaving
only the grains of gold.
Another contrivance which soon came into use was the "cradle." This
was a long box, sometimes only a hollowed-out log. At the top was a
sieve which sifted out the stones. Nailed to the bottom of the cradle
were small cleats of wood, or "riffles," which kept the water from
running so fast as to sweep the gold out of the cradle with it. The
cradle was placed on rockers and was also tilted slightly. The miner
shoveled the gravel into the top of the cradle and his partner rocked
it. The sieve kept back the stones, the water broke up the lumps of
earth and gravel and washed them down the cradle, and the grains of
gold were stopped by the riffles, and sank to the bottom. Sometimes
the "pay dirt" continued under a stream. To get at it, the miners
often built a little canal and turned the water into a new channel;
then they could work on the former bed of the river.
Before many years had passed, the gold that was near the surface had
been gathered. The miners then followed the streams up into the
mountains, and found that much of the gold had come from beds where in
ancient times rivers had flowed. There was gold still remaining in
these beds, but it was poorly distributed, the miners thought.
Sometimes there would be quite an amount in one place, and then the
miner would dig for days without finding any more. Even worse than
this was the fact that these gravel beds were not on the top of the
ground, but were covered up with soil and trees. Evidently the slow
work with pans and cradles would not pay here; but it occurred to some
one that if a powerful stream of water could be directed against the
great banks of earth, as water is directed against a burning building,
they would crumble, the dirt could be washed down sluices, and the
gold be saved. This was done. Great reservoirs were built high up in
the mountains, and water was brought by means of ditches or pipes to a
convenient place. Then it was allowed to rush furiously through a
hose and nozzle, and the great stream coming with tremendous force was
played upon the banks of gravel. The banks crumbled, the gravel was
washed into a string of sluices, or long boxes with riffles to catch
the gold. Soon the miners found that if quicksilver was put into these
sluices, it would unite with the gold and make a sort of paste called
"amalgam." Then if this amalgam was heated, the quicksilver would be
driven off in the form of gas, and the gold would remain in a
beautiful yellow mass.
[Illustration: HYDRAULIC GOLD MINING
A placer mine at Gold Point, California, where tremendous streams of
water under high pressure are busy washing away the side of a
gold-bearing hill.]
The ancient rivers had also carried gold to the valleys, and to
collect this a dredge, which the miners called a "gold ship," came
into use. The "ship" part of this machine is an immense flat scow.
Stretching out from one end is something which looks like a moving
ladder. This is the support of an endless chain of buckets, each of
which can bite into the gravel and take a mouthful of five or six
hundred pounds. They drop this gravel into a big drum which is
continually revolving. Water flows through the drum, and washes out
the sand and bits of gold over large tables, where by means of riffles
and quicksilver the gold is captured. This scow was usually on dry
land at first; but its digging soon made a lake, and then it floated.
It must be more fascinating to hold a pan in your own hands and pick
out little grains of gold or perhaps even a big piece of it with your
own fingers, but if the gravel is good the dredge makes more money.
In Alaska the great difficulty in mining is that, except at the
surface, the ground is frozen all the year round. At first, the miners
used to thaw the place where they wished to dig by building wood
fires; but this was a slow method, and now the thawing is done by
steam. They carry the steam in a pipe to the place where the digging
is to be done, and send it through a hose. At the end of the hose is a
pointed steel tube. They hammer this tube into the ground and let some
steam pass through the nozzle. This softens the ground so that picks
and shovels may be used. There is generally cold enough in Alaska, but
once at least the miners had to manufacture it. The gold-bearing
gravel was deep, the ground was flat, and it was often overflowed.
They set up a freezing plant, and shut in their land with a bulkhead
of ice several feet thick. Then they pumped out what water was already
in and did their work with no more trouble.
When gold began to grow less in the California gravel, the miners
looked for it in the rocks on the mountain-side. The placer miners
laughed at them and called their shafts "coyote holes"; but in time
the placers failed, while nearly all of our gold to-day comes from
veins of white quartz in the rocks. A vein of gold is the most
capricious thing in the world. It may be so tiny that it can hardly be
seen, then widen and grow rich in gold, then suddenly come to an end.
This is why a new mine is so uncertain an enterprise. The gold may
hold out and bring fortunes to the investors, or it may fail, and then
all they will have to show for their money is the memory that they
put it into a hole in the ground. The managers of a few of the
well-established mines, however, have explored so far as to make sure
that there is gold enough for many years of digging.
The mining engineer must be a very wide-awake man. It is not enough
for him simply to remember what was taught him in the schools of
mining; he must be bright enough to invent new ways of meeting
difficulties. No two mines are alike, and he must be ready for all
sorts of emergencies. A gold mine now consists of a shaft or pit dug
several hundred feet down into the rock, with levels or galleries
running off from it and with big openings like rooms made where the
rock was dug out. The roofs of the rooms are supported by great
timbers. To break away the rock, the miner makes a hole with a rock
drill worked by electricity or compressed air, puts powder or dynamite
into the hole and explodes it. The broken rock is then raised to the
surface and crushed in a "stamping mill." Here the ore is fed into a
great steel box called a "mortar." Five immense hammers, often
weighing a thousand pounds apiece, drop down upon the ore, one after
another, until it is fine enough to go through a wire screen in the
front of the box. When two hundred or more of these hammers are
pounding away with all their might, a stamping mill is a pretty noisy
place. The ore, crushed to a fine mud, now runs over sloping tables
covered with copper. Sticking to the top of the copper is a film of
quicksilver. This holds fast whatever gold there may be and makes an
amalgam, which is scraped off from time to time, and the quicksilver
is driven from the gold by heat.
Gold that is not united with other metals is called "free milling
gold." Much of it, however, is found in combination with one metal or
another, and is known as "rebellious" or "refractory" gold. Such gold
may sometimes be set free by heat, and sometimes by chemicals. One way
is by the use of chlorine gas, and the story of it sounds almost like
"The house that Jack built." It might run somewhat like this: This is
the salt that furnishes the chlorine. This is the chlorine gas that
unites with the gold. This is the chloride that is formed when the
chlorine gas unites with the gold. This is the water that washes from
the tank the chloride that is formed when the chlorine gas unites with
the gold. This is the sulphate of iron that unites with the chlorine
gas of the chloride that the water washes from the tank that is formed
when the chlorine gas unites with the gold--and leaves the gold free.
Another method is by the use of cyanide. More than a century ago a
chemist discovered that if gold was put into water containing a little
cyanide, the gold would dissolve, while quartz and any metals that
might be united with the gold would settle in the tank. The water in
which the gold is dissolved is now run into boxes full of shavings of
zinc and is "precipitated" upon them; that is, the tiny particles of
gold in the water fall upon the zinc and cling to it. Zinc melts more
easily than gold, so if this gilded zinc is put into a furnace, the
zinc melts and the gold is set free.
Very often gold is found combined with lead or copper. It must then be
melted or smelted in great furnaces. The metal is heavier than the
rock and settles to the bottom of the furnace. It is then drawn off
and the gold is separated from the other metals, usually by
electricity.
Sometimes large pieces of gold called "nuggets" are found by miners.
The largest one known was found in Australia. It weighed 190 pounds
and was worth $42,000. Sometimes spongy lumps of gold are found; but
as a general thing gold comes from the little specks scattered through
veins in rock, and much work has to be done before it can be made into
coins or jewelry. It is too soft for such uses unless some alloy,
usually copper or silver, is mixed with it to make it harder.
Sometimes it is desirable to know how much alloy has been added. The
jeweler then makes a line with the article on a peculiar kind of black
stone called a "touchstone," and by the color of the golden mark he
can tell fairly well how nearly pure the article is. To be more
accurate, he pours nitric acid upon the mark. This eats away the alloy
and leaves only the gold.
Gold is a wonderful metal. It is of beautiful color; it can be
hammered so thin that the light will shine through it; few acids
affect it, and the oxygen which eats away iron does not harm it. Pure
gold is spoken of as being "twenty-four carats fine," from _carat_, an
old weight equal to one twenty-fourth of an ounce troy. Watchcases
are from eight to eighteen carats fine; chains are seldom more than
fourteen; and the gold coins of the United States are about eleven
parts of gold and one of copper. Coins wear in passing from one person
to another, and that is why the edges are milled, so that it may be
more easily seen when they have become too light to be used as coins.
When such pieces come into the hands of the Government, they must be
recoined.
VI
THE STORY OF A SILVER MINE
A man who goes out in search of a mine is called a "prospector." The
best prospector is a man who has learned to keep his eyes open and to
recognize the signs of gold and silver and other metals. A faithful
friend goes with him, a donkey or mule which carries his bacon and
beans, blankets, saucepan, and a few tools, such as a pan, pick,
shovel, hammer, and axe. Sometimes the prospector also takes with him
a magnifying glass and a little acid to test specimens, but usually he
trusts to his eyes alone.
When these few things have been brought together, the prospector and
the donkey set out. They wander over the hills and down into the
canyons. If a rock is stained red, the prospector examines it to see
whether it contains iron; if it is green, he looks for copper. In the
canyons and along the creeks he often tests the gravel for traces of
some valuable metal. If he finds any of these traces along the stream,
he follows them on the bank until they stop; then he carefully
examines the bank of the stream or the nearest hillside. If he
continues to find bits of metal, they will lead him to a vein of ore,
from which they have been broken by the wind, rain, and frost.
Generally a prospector is looking for some one special metal, and in
his search he often overlooks some other metal; for instance,
thousands of the gold-seekers who rushed to California in 1849 hurried
through Nevada on their way. If they had only known what was under
their feet, they would have taken their picks and shovels and begun to
dig, instead of trying to get out of the region as soon as might be.
Ten years later, the California placers were becoming exhausted, and
miners began to go elsewhere in their search for gold.
Among those who were working in what is now the State of Nevada were
two Irishmen who had been unlucky in California and had fared no
better in Nevada. They wanted to go somewhere else, but they had not
money enough for the journey; so they kept on with their work at the
foot of Mount Davidson, washing the gravel and saving the little gold
that they found. They were annoyed by some heavy black stuff that
united with the quicksilver in their cradles, interfered with the
saving of the gold, and put them in a very bad temper. At length a man
named Henry Comstock came along, who told them that this black stuff
was silver ore. They examined the mountain-side, and discovered the
outcrop or edge of a great vein containing gold and also silver. It is
no wonder that people rushed from the east and west to the wonderful
new mines, for it was plain that these new "diggings" were not mere
placers, but rich veins that many years of working might not exhaust.
Every newcomer hoped to discover a vein; and within a year or two the
district around the Comstock lode was full of deep shafts, many of
them abandoned and half-hidden by low brush, but some of them yielding
quantities of gold and silver. Before this, there had been only about
a thousand people in what is now Nevada, but in two years after the
discovery of silver, there were 16,000, and a new Territory was
formed.
The miners knew how to get gold out of ore, but silver was another
matter, and some of it was difficult to extract. They had so much
trouble that they were ready to believe in any treatment of the ore,
no matter how absurd, that promised to help them out of their
difficulties. Some of them were actually persuaded that the juice of
the wild sagebrush would bring the silver out. It is no wonder that
they were troubled, for in the Comstock lode were not only gold and
silver, but ten or twelve other metals or combinations of silver with
something else. At length processes were invented for treating the
different kinds of ore. Some kinds were crushed in a stamping mill,
then ground to a powder and mixed with quicksilver or mercury. This
mercury united with both the gold and the silver, making an amalgam.
The amalgam, together with the finely ground ore, was put into a
"settler," and here the heavy amalgam sank to the bottom and was then
strained. The extra mercury was collected, and the amalgam was put
into a retort or kettle and heated. The mercury became a gas and was
driven off from the gold and silver, then caught in a vessel cool
enough to condense it, just as a cold plate held in steam will
collect drops of water. Sometimes the ore was mixed with copper and
lead. In that case common salt and copper sulphate were used. Some ore
had to be roasted in a furnace in order to drive off the sulphur.
[Illustration: THE STORY OF A SPOON
_Courtesy The Gorham Co._
(1) Silver strip blanked. (2) Pinched. (3) Graded. (4) Outlining of
Handle. (5) Stamped Handle. (6) Spoon completely trimmed. (7, 8)
Finished spoons.]
There were great and unusual dangers to be met in getting the ore. The
vein of quartz which bore it was fifty or sixty feet wide. Some was
hard, and some so soft and crumbling that pillars would not hold up
the roof. The passageways were then lined with heavy logs standing on
either side, other logs laid across their tops, and all bolted firmly
together. Nevertheless, they twisted and fell, and slowly but
certainly the whole mass of earth and rock, two hundred or more feet
in thickness, was coming down upon the heads of the miners. The work
on the Comstock mines had come to an end unless a man could be found
able to invent some system of support not laid down in the books. The
man was found. He took short, square timbers five or six feet long,
put them together as if they were the sides and ends of square boxes,
and piled them one above another, making hollow pillars. He fastened
these firmly together and filled the space inside with waste rock,
thus making strong, solid pillars that would support almost any weight
that could be put upon them.
There were two other dangers, water and heat. The vein was porous and
water was constantly trickling out of it. Then, too, there were "water
pockets," or natural reservoirs in the rock, and any moment the
stroke of a pick might let out a torrent and force the miners to run
for their lives. Sometimes minerals were dissolved in this water, and
the men with closed eyes and swollen faces had to be hurried to the
surface for treatment. Powerful pumps had to be used and the water
sent away through long lines of pipes. This water was warm, and in
very deep workings in the Comstock vein it was boiling hot. Even with
quantities of ice sent down to cool them, the men could work in some
places only a short time.
In San Francisco there was a mining engineer named Adolph Sutro who
planned to remedy these troubles by driving a big four-mile tunnel
through the heart of the mountain, letting out the hot water and the
foul air. The owners of some of the mines joined him in raising the
money, and the tunnel was dug. Through this the water ran out. The
mines were freed of foul air and fresh air was driven in.
The Comstock lode has given up an amazing amount of precious metal.
Between 1860 and 1890 it produced $340,000,000. After 1890, however,
its product grew less. The vein was not so rich, the price of silver
fell, while the cost of mining it at great depths increased. Not
nearly so much was mined, and at length water rose in the mines up to
the level of the Sutro Tunnel. In 1900 new machinery was put in and
new methods were adopted, such as treating the tailings with cyanide
and so saving much of the precious metal from them. From the beginning
the Comstock mines have been so ready to follow improved methods that
they have been called the mining school of the world.
Great quantities of silver are used for making jewelry and for
tableware. The one objection to its use is that silver likes to unite
with sulphur, and thus the silver easily becomes black. There is
sulphur in the yolk of an egg and that is why the spoon with which it
has been eaten turns black. Even if silverware is not used, it
tarnishes, especially in towns, because there is so much sulphureted
hydrogen in the air. In perfectly pure air, it would not tarnish.
Silver is harder than gold, but not hard enough to be used without
some alloy, usually copper. Tableware is "solid" even if it contains
alloy enough to stiffen it. It is "plated" if it is made of some
cheaper metal and covered with silver. The old way of doing this was
to fasten with bits of solder a thin sheet of silver to the cup or
vase or whatever was in hand and heat it. This did fairly well for
large, smooth articles; but it was almost impossible to finish the
edges of spoons so as not to show the two metals. If you look at a
plated spoon to-day, however, you will find that there is no break at
the edge, and so far as you can tell by the eye, it is solid silver.
If you look on the back of the spoon, you will perhaps see "Rogers
Bros. 1846." These men were the first silvermakers in this country to
plate tableware by electricity. To make a spoon, they formed one out
of iron or copper and made sure that it was perfectly clean. Then
across a bath of silver cyanide, potassium cyanide, and water they
laid two metal rods, and from these they hung a spoon at one end and a
plate of silver at the other. These rods were connected with the two
poles of a battery. The electrical current passed through them,
released the silver from the silver cyanide, and this was deposited
upon the spoon. The cyanide that had lost its silver took enough more
from the silver plate to make up. The amount of silver on the spoon
depends upon the length of time it remains in the bath. It is weighed
before plating and again afterwards, to make sure that the proper
amount of silver has been deposited upon it. On the back of many
plated articles you will see the words "Triple plate" or "Quadruple
plate." If the article has been made by a reliable firm, this means
that the triple plate it manufactures contains three times as much
silver as "single plate," and that quadruple plate contains four times
as much. A piece of silver looks just as well if it has stayed in the
bath only a few minutes, but of course it has taken on so little
silver that this will soon wear off and show the cheaper metal.