n 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 pe