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Page 19
In this engine, if it can be called an engine, we see that the Marquis
had a good idea of the power of steam, but he had none, you will
observe, as to the action of the condensation which would immediately
take place when the steam from the boiler was brought into contact with
the cold water to be raised. Therefore this plan would be most
expensive, on account of the great loss of steam by condensation. It
was, however, quite able to produce the effect, though only equal to
raising 20 cubic feet of water, or 1250 lbs., one foot high by one pound
of coal, or about the two-hundredth part of the effect of a good
steam-engine. After this, of course, it proved of no avail; but still we
may say that the Marquis of Worcester was among the first who tried to
make, and did do so, steam a moving power.
Our next is Denys Papin (died 1710), a native of Blois, in France, who
was mathematical professor at Marpurg. To him is due the discovery of
one of the qualities of steam--its condensation, so as to produce a
vacuum, to the proper management of which our modern engines owe much of
their efficacy. Papin seems to have been the first who conserved the
idea of the cylinder and piston, which he made to act on atmospheric
principles--that is to say, he took a cylinder with a piston moving up
and down in it, and found that by removing the air from under the piston
in the cylinder, that the pressure of the atmosphere would drive it down
to the bottom of the cylinder: this he performed by admitting steam, and
then condensing it rapidly, so causing the required vacuum. The pressure
of the atmosphere is as near as may be 16 lbs. on every square inch of
surface on the globe: this is obviously the weight of the columns of
air extending from that square inch of surface upwards to the top of the
atmosphere. This force is thus measured: Take a glass tube 32 inches
long, open at one end and closed at the other; provide also a basin full
of mercury; let the tube be filled with mercury and inverted into the
basin. The mercury will then fall in the tube, till it gets to that
height which the atmosphere will sustain. This is nothing more than the
barometer used in all our houses. If the action of the tube be equal to
a square inch, the weight of the column of mercury in the tube would be
exactly equal to the weight of the atmosphere on each square inch of
surface. Thus Papin discovered a great step in the steam-engine, though
it was not much acted on for some years; he was also the first who
proposed to drive ships with paddles worked by steam.
We now come to Thomas Savory, who got a patent in 1698 for a method of
condensing steam to form a vacuum. Savory describes his discovery in
this way:--Having drank a flask of wine at a tavern, he flung the empty
flask on the fire, and then called for a basin of water to wash his
hands. A little wine remained in the flask, which of course soon
boiled, and it occurred to him to try what effect would be produced by
putting the mouth of the flask into the cold water. He did this, and in
a moment the cold water rushed up and filled the flask, this being
caused by the steam being condensed and leaving a vacuum, which Nature
abhors, and rather than permit this the water rushed up and took the
place formerly occupied by the now condensed steam. We see by this in
how simple a way great ends are produced, and in the age in which this
happened, the result may be indeed be said to have produced a great end.
The engine of Savory was used for some years as a machine to raise
water. The principle of his engine was just as I have stated, and
consisted of two cases and other various parts, and this engine
possessed advantages over that of the Marquis of Worcester in sucking up
the water as well as forcing.
Savory's engine consisted of two steam vessels connected to a boiler by
tubes; a suction pipe, or that pipe which leads from a pump of the
present day to the well, and communicating with each of the steam
vessels by valves opening upwards; a pipe going from these steam vessels
to any required height to which the water is to be raised. The steam
vessels were connected to this pipe by other valves, also opening
upwards, and by pipes. Over the steam vessels was placed a cistern,
which was kept filled with _cold_ water. From this proceeded a pipe with
a stopcock. This cistern was termed the condensing cistern, and the pipe
could be brought over each steam vessel alternately from the boiler.
Now, suppose the tubes to be filled with common air, and the regulator
placed so that one tube and the boiler are made to communicate, and the
other tube and the boiler closed, steam will fill one of the steam
vessels through one tube; at first it will condense quickly, but erelong
the heat of the steam will impart its heat to the metal of the vessel,
and it will cease to condense. Mixed with the heated air, it will
acquire a greater force than the air outside the valve, which it will
force open, and drive out the mixture of air and steam, till all the air
will have passed from the vessel, and nothing but the vapour of water
remain. This done, a cock is opened, and the water from the cistern is
allowed to flow over the outside of the steam vessel, first having
stopped the further supply of steam from it; this produced the
immediate condensation of the steam contained in it, by the temperature
being brought down again by the cold water, and the condensation thus
produced caused a vacuum inside the vessel. The valve will then be kept
closed by the atmosphere outside, and the pressure of the air on the
surface of the water in the well or reservoir will open another valve,
force the water up the pipe, till, after one or two exhaustions--if I
may so term it--it will at last reach the second vessel. Thus far the
atmosphere has done all the work, but at last the water fills the
vessel, and then comes the forcing point. Now the power of the steam
itself is used to drive the water up the pipe. The steam is again let
into the vessel, now filled in whole, or at least in great part, with
water; at first it will, as before, condense rapidly, but soon the
surface of the water will get heated, and as hot water is lighter than
cold, it will keep on the surface, and the pressure of the steam from
the boiler will drive all the water from the vessel up the pipe. When it
is empty the cock is again opened, and the steam, which the vessel by
this time only contains, is again condensed, and the same process which
I have just described is again commenced and carried out, thus making
Savory's engine a complete pump by the aid of the vapour of water as
raised by fire.
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