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Page 21
The weight of steam is about 1800 times less than water. I may here
perhaps mention also that water will boil at 100 degrees Fahr. in vacuo,
whereas in atmosphere it takes 212 degrees to boil. There is also a
thing perhaps worth knowing to all who wish to get the most stock out of
bones, &c., that if they are boiled in a closed vessel, that is to say,
under a pressure of steam, a very large increase in quantity of the
stock will be produced, because the heat is increased. A cubic inch of
water, evaporated under _ordinary_ atmospheric pressure, will be
converted into a cubic foot of steam; and a cubic inch of water,
evaporated as above, gives a mechanical force equal to raising about a
ton a foot high.
The next great improvement of Watt, in addition to the condenser, is the
air-pump, the use and absolute necessity for which you will understand
when I explain its action. Watt first used it for his atmospheric
engine. The piston of this engine was kept tight by a flow of oil and
water on the top, which tended to make the whole a troublesome and
bad-working machine. The cold atmosphere, as the piston went down, of
course followed it and cooled the cylinder. On the piston again rising,
some steam would of course be condensed and cause waste. If the
engine-room could be kept at the heat of boiling water, this would not
have been the case, but the engineman who could live in this heat would
also require to be invented, and so this had to be given up. Watt's next
and most important step was the one which brings us to talk of the
steam-engine as it now is in the present day. This important step was
the idea, of making the steam draw down the piston, as well as help to
drive it up; in the first engines it was raised by the beam, and steam
used only to cause a vacuum, so as to let the air drive it down. All
before this had been merely steps in advance, like those of children,
who must walk before they can run; so was it with the steam-engine. It
was uphill work for many years, and the top of the hill cannot be said
to have been readied till Watt worked out this grand idea. The first
engine could only be called atmospheric; now it was destined to become
in reality a steam-engine. Time would fail were I to attempt to go into
any details of all the experiments through which Watt toiled to bring
his ideas to perfection--enough to say that he did so; and I trust you
will be able, through the description I will endeavour to give, to
understand how well his labour was bestowed, and how beautiful the
result has proved for the benefit of the world at large. In 1773, Watt
removed to Soho, near Birmingham, where a part of the works was allotted
to him to erect the machinery necessary to carry out his inventions on a
grand scale.
We must now proceed to some of the useful points of the engine, all I
have before mentioned simply relating to the inventors and improvers;
but having brought it so far, I may now, I think, proceed further. The
first use of the steam-engine was simply to raise water from mines, and
for long it was thought it could be used for nothing else; so much so,
that it was at one time used to raise water to turn wheels and thus
produce motion. One of its first uses after it became a really useful
machine was to propel ships, though many a weary hour was spent to bring
it to this point. There is a very pretty monument on the Clyde,
dedicated to Mr. Bell, who I believe was the first person who
successfully brought steamers to work on its waters. The first who used
steam for ships was Mr. James Taylor, in conjunction with Mr. Miller of
Dalswinton. The danger of the fire-ship took such hold on people's minds
that it was with great toil and difficulty they were persuaded to
venture on the face of the waters in such dangerous and unseamanlike
craft. But go to Glasgow Bridge any day, and you will see how time has
overcome fear and prejudice, for our ocean is covered with steamers of
all sizes. It is not many years ago since it was said that steamers
could never reach America; this has given way to proof, and even
Australia has been reached by steam. I know of a steamer building which
could carry the whole population of this place and not be full; she is
680 feet or 226 yards long, and a large vessel would hang like a boat
alongside her.
The first attempt at giving motion by steam to ships was of course only
in one way--by a ratchet at the end of a beam, at one moment driving
and the next standing still. This was on account of the engine being
only in power one half of the stroke; but by the double-acting engine
being introduced, and the steam acting both ways, it became at last a
steady mover (without the aid of two or three cylinders, as in the first
engines, one to take up the other as the power was given off), by a
ratchet on the end of a beam or else a chain. This acted on the shaft
which moved the paddles. It is to Watt that we are indebted for the
crank and direct action, so as to give a circular motion to the wheels.
We find in 1752 a Mr. Champion of Bristol applied the atmospheric engine
to raise water to drive a number of wheels for working machinery in a
brasswork, in other words, a foundry. Also, in Colebrokedale,
steam-engines were used to raise water that had passed over the wheel,
so as to save water. All these plans have, however, now passed by, like
the water over the wheel, and we now have the engine the prime
mover--the double action of the steam on the piston, this acting on the
sway beam, and the beam on the crank, which, by the assistance of the
fly-wheel on land or fixed engines, gives a uniform motion to the
machine. All these have now enabled us to apply the engine as our grand
moving power. One great and important point in the engine is the
governor, and the first modes of changing the steam from the top to the
bottom of the cylinder were cumbrous, till the excentric wheel was
devised.
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