CERTAIN IMPROVE- MENTS IN THE CONSTRUCTION OF STEAM ENGINES
Year: 1804

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ARTHUR
WOOLF, of Wood Street, Spa Fields, in the County of Middlesex, Engineer,
send greeting.
WHEREAS His present most Excellent Majesty King George the Third,
in and by His Letters Patent under His Great Seal of the United Kingdom of
Great Britain and Ireland, bearing date at Westminster, the Seventh day of
June, in the forty-fourth year of His reign, for Himself, His heirs and successors,
did give and grant unto me, the said Arthur Woolf, my executors, administrators,
and assigns, His especial licence, full power, sole privilege and authority,
that I, the said Arthur Woolf, my executors, administrators, and assigns, and
every of them, by myself and themselves, or by my and their deputy or deputies,
servants or agents, or such others as I, the said Arthur Woolf, my executors,
administrators, or assigns, should at any time agree with, and no others, from
time to time and at all times thereafter during the term of years therein expressed,
should and lawfully might make, use, exercise, and vend, within that part of
His said Majesty's United Kingdom called England, His Dominion of Wales,
and the Town of Berwick-upon-Tweed, my Invention of "CERTAIN IMPROVE-
MENTS IN THE CONSTRUCTION OF STEAM ENGINES;" in which said Letters Patent
there is contained a proviso obliging me, the said Arthur Woolf, by an instrument
in writing under my hand and seal, particularly to describe and ascertain the
nature of my said Invention, and in what manner the same is to be per-
formed, and to cause the same to be inrolled in His said Majesty's High Court

page_text: of Chancery within one calendar month next and immediately after the date of
the said recited Letters Patent, as in and by the same, relation being thereunto
had, will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Arthur Woolf, do hereby describe and ascertain the nature of my said Invention,
and the manner in which the same is to be performed, as follows, that is
to say:-
I have ascertained by actual experiments, and have applied the same to
practice, that as in practice it is found that steam, acting with the expansive
force of four pounds the square inch against the safety valve exposed to the
atmosphere, is capable of expanding itself to four times the volume it then
occupies, and still to be equal to the pressure of the atmosphere, so in like
manner steam of the force of five pounds the square inch can expand itself to
five times its volume. Masses or quantities of steam of the like expansive
force of six, seven, eight, nine, or ten pounds the square inch can expand
itself to six, seven, eight, nine, or ten times its volume, and still be respectively
equal to the atmosphere, or capable of producing a sufficient action against the
piston of a steam engine to cause the same to rise in the old engine (with a
counterpoise) of Newcomen, or to be carried into the vacuous part of the
cylinder in the improved engines first brought into effect by Boulton and Watt,
and this ratio is progressive, and nearly if not entirely uniform, so that steam
the expansive force of twenty, thirty, forty, or fifty pounds the square inch of
a common safety valve will expand itself to twenty, thirty, forty, fifty times its
volume, and generally as to all the intermediate or higher degrees of clastic
force, the number of times which steam of any temperature and force can
expand itself, being nearly the same as the number of pounds it is able to
sustain on a square inch exposed to the common atmospheric counter pressure,
provided always that the space, place, or vessel in which it is allowed to expand
itself be at least of as high a temperature, or nearly as high a temperature, as
that of the steam before it be allowed room to expand, that is, whatever be the
degree of heat necessary to the permanency of steam of the force of twenty
pounds the square inch, if steam of that force be employed, the space, place,
or vessel in which it is allowed or intended to expand itself should be of the
same temperature or nearly so; and so with steam of any other power as of
thirty, forty, or fifty pounds the square inch, the space, place, or vessel in
which it is to expand should be at or about the same degree of heat as
steam of the force employed requires for its existence; in which case, as I
have before stated, steam can expand itself about as many times as the
number of pounds it could have sustained on a square inch, as aforesaid, before

page_text: it is allowed to expand or dilate itself. Here, however, it may be necessary
to remark that in stating this ratio I only speak of the expansion of steam as
it can be managed and commanded in practice, and not of the absolute ex-
pansion which perhaps might be obtained if mechanism could be made so
perfect as to prevent all escape of steam and all partial condensation of it and
waste of heat. For the real expansive force of steam I am inclined to
believe, from the experiments I have made, increases in a regular ratio a
little beyond what I have stated, though I would not recommend that it
should be calculated higher in applying it to steam engines because the
difficulty of confining and managing it increases also as the clasticity of the
steam is increased, or as its temperature is increased. And here it may be of
use to the public to state soine facts respecting different degrees of temperature
required to bring steam to and maintain it at different expansive forces above the
weight of the atmosphere, because the temperature of the steam indicated by a
thermometer having its bulb in the boiler which produces it will indicate the
expansive force of the steam without the trouble and inconvenience of chang-
ing the weights on the valve by which its force is regulated for the work
intended to be performed by it, and which valve acts as a cominon safety valve,
so that those who attend the boiler will know with suflicient precision by
looking at the thermometer, how they ought to feed the fire, and moreover,
the relation between the temperature and the expansive force being known,
the danger of accidents from the safety valve becoming deranged will be
lessened, for the workman will naturally be led to notice whether the safety
valve acts freely when the thermometer has risen to the degree that answers to
the weight with which the valve is loaded for working. I have found by
actual experiment, setting out from the boiling point, or two hundred and
twelve degrees of the thermometer commonly employed in this country, which
is that of Fahrenheit, at which degree steam of water is only equal to the
pressure of the atmosphere, that in order to give it an increased elastic force
equal to five pounds the square inch the temperature must be raised 15° or 16°
degrees, or to about 227, when the steam will have acquired a power to
expand itself to five times its volume, and still be equal to the atmosphere, and
capable of being applied as such in the working of steam engines according
to my said Invention. And with regard to various other pressures, tempera-
tures, and expansive forces of steam, the same are shewn in the following
table-
Table of the relative pressures per square inch. Temperatures and expan-
sibility of steam at degrees of heat above the boiling point of water, beginning
with the emperature of steam of an elastic force equal to five pounds per

page_text: and so, in like manner, by small additions of temperature, an expansive power
may be given to steam to enable it to expand to fifty, sixty, seventy, eighty,
ninety, one hundred, two hundred, three hundred, or more, times its volume,
without any limitation but what is imposed by the frangible nature of every
material of which boilers and the other parts of steam engines have been or can
be made; and prudence dictates that the expansive force should never be
carried to the utmost the materials can bear, but rather be kept considerably
within that limit.
Having thus fully explained my discovery of the expansive power and force
of steam, I shall proceed to describe my improvements grounded thereon, and
in so doing I shall find it necessary to mention the entire steam engine and
its parts, to which, as an invention well known, I neither can nor do assert
any exclusive claim; but at the same time I must here observe that, from the
nature of the aforesaid discovery and its application, there can be no difficulty
in distinguishing my said improvements from the improved engine as to its
other common and well known component parts.
First. If the engine be constructed originally with the intention of adopting
my said improvements, it ought to have two steam vessels of different dimen-
sions, according to the temperature or the expansive force determined to be
communicated to the steam made use of in working the engine, for the smaller
steam vessel or cylinder must be a measure for the larger. For example, if
steam of forty pounds the square inch is fixed on, then the smaller steam
vessel should be at least one fortieth part the contents of the larger one. Each
steam vessel should be furnished with a piston, and the smaller cylinder

page_text: should have a communication both at its top and bottom (top and bottom
being here employed merely as relative terms, for the cylinders may be
worked in a horizontal or any other required position as well as vertical).
The small cylinder, I say, should have a communication both at its top and
bottom with the boiler which supplies the steam, which communications, by
means of cocks or valves of any construction adapted to the use, are to be
alternately opened and shut during the working of the engine. The top of the
small cylinder should have a communication with the bottom of the larger
cylinder, and the bottom of the smaller one with the top of the larger, with
proper means to open and shut these alternately by cocks, valves, or any other
well known contrivance, and both the top and bottom of the larger cylinder or
steam vessel should, while the engine is at work, communicate alternately with
a condensing vessel, into which a jet of water is admitted to hasten the con-
densation; or the condensing vessel may be cooled by any other means calcu-
lated to produce that effect. Things being thus arranged, when the engine is
at work, steam of high temperature is admitted from the boiler to act by its
elastic force on one side of the smaller piston, while the steam which had
last moved it has a communication with the larger steam vessel or cylinder,
where it follows the larger piston now moving towards that end of its cylinder
which is open to the condensing vessel. Let both pistons end their stroke at
one time, and let us now suppose them both at the top of their respective
cylinders ready to descend, then the steam of forty pounds the square inch
entering above the smaller piston will carry it downwards, while the steam
below it instead of being allowed to escape into. the atmosphere or applied to
other purpose, will into the larger cylinder above its piston, which
pass
will take its downward stroke at the same time that the piston of the smallor
cylinder is doing the same thing, and while this goes on the steam which last
filled the larger cylinder in the upward stroke of the engine will be passing
into the condenser to be condensed during the downward stroke.. When the
pistons in the smaller and larger cylinder have thus been made to descend to
the bottom of their respective cylinders, then the steam from this boiler is to
be shut off from the top and admitted to the bottom of the smaller cylinder,
and the communication between the bottom of the smaller and the top of the
larger cylinder is also to be cut off and the communication to be opened
between the top of the smaller and the bottom of the larger cylinder, the
steam which in the downward stroke of the engine filled the larger cylinder
being now open to the condenser, and the communication between the bottom
of the larger cylinder and the condenser shut off, and so on alternately
admitting the steam to the different sides of the smaller. piston, while the:
any

page_text: steam last admitted into the smaller cylinder passes alternately to the different
sides of the larger piston in the larger cylinder, the top and bottom of which
are made to communicate alternately with the condenser. In an engine
working with the improvements which have been just described while the
steam is admitted to one side of the piston in the smaller cylinder, the
steam on the other side has room made for its admission into the larger
cylinder on one side of its piston by the condensation going on, on the other
side of the large piston which is open to the condenser, and that waste of
steam which takes place in engines worked only by the expansive force of
steam from steam passing the piston is prevented, for all steam that passes the
piston in the smaller cylinder is received into the larger. In such an engine,
where it may be more convenient for any particular purpose, the arrangement
may be altered and the top of the smaller made to communicate with the top
of the larger, and the bottom of the smaller with the bottom of the larger
cylinder, in which case the only difference will be that when the piston in
the smaller cylinder descends, that in the larger will ascend, and while the
latter descends the former will ascend, which for some particular purposes may
be more convenient than the arrangement before described.
Secondly. As the difficulty of giving a proper degree of strength to large
cylinders, and the cases for the same that are to be exposed to the action of
strong steam, increases in proportion as their size is augmented, instead of
employing besides the smaller cylinder or steam measure one cylinder only of
large diameter, in steam engines of great power I sometinies prefer substi-
tuting for the latter cylinder two or more cylinders of snaller diameter, but of
such dimensions that their capacity, and the area of the pistons worked in
them, are equal to the area of the one piston and the capacity of the one
cylinder which otherwise would be necessary; and such substituted cylinders
are made to communicate with each other, that they may at one and the same
time receive and part with the steam by which the engine is worked, and their
respective piston rods are so connected with one another, or with other
parts of the machinery, that the pistons may act together.
Thirdly. With regard to steam engines which are already constructed, I
improve the same by adding thereto a small cylinder or measure for the steam
admitted to the working cylinder. This improvement may be introduced with
great advantage into the steam engines constructed according to Mr. Watt's im-
provements; which small cylinder may either be employed only as a measure of
the steam, or a piston may be worked in it by the expansive force of the steam
before it be allowed to pass into the present working cylinder or steam vessel,
which in that case must have no direct communication with the boiler, but.

page_text: must be supplied with steam through the medium of the small added cylinder
or steam measure. To make this more intelligible, suppose the steam measure
or small cylinder added to one of Mr. Watt's singlo engines, or to one of
similar construction, and that the small added cylinder is furnished with a
piston to work by the expansive force of the steam, while the larger cylinder
works by condensation, then all that is necessary is, that the top of the smaller
added cylinder be connected with the boiler, and furnished with a cock or
valve to shut off the steam, and the boiler be of sufficient strength; let a pipe
pass from the top to the bottom of the smaller added cylinder, furnished with
a cock or valve, by which a communication may be made between the two
sides of the piston in the said cylinder; let a pipe also pass from the bottom
of the smaller cylinder to the top of the larger; let the larger cylinder, as is
now commonly the case in practice, have a pipe passing from its top to its
bottom, by which a communication can be made between the two sides of
the piston in the large cylinder, and let the largo cylinder communicate with
a condensing vessel with valves, cocks, or any other contrivance to open or shut
the different communications when necessary. Things being thus arranged,
suppose the engine at work, and the pistons in both cylinders at the top of
their respective cylinders, and suppose the steam admitted to enter the small
cylinder above the piston, while the steam is thus entering, let the communi-
cation between the bottom of the small cylinder and the top of the large one
be open, while the bottom of the large one is open to the condenser, then both
pistons will descend. When they have reached the bottom of their respective
cylinders the communications between the boiler and small cylinder, between
the small and large cylinder, and between the latter and the condenser, must
all be shut off, and the communications must be opened between the two sides
of the smaller piston and between the two sides of the larger piston; then, as
the pistons ascend the steam which was last admitted above the small piston
will pass to its under side, while the steam which was last admitted to the top
of the large from the lower part of the small cylinder will pass into the lower
part of the large cylinder under its piston, and both pistons will at the same
time ascend by the action of the counterweight or the momentum of the fly, as
the case may be. When both pistons have reached the top of their respective
cylinders, the last-mentioned communications are shut and the others are opened
as before, and both will descend; the steam which was last admitted to the
underside of the small piston passing into the upper end of the large cylinder,
while the steam last introduced below the piston of the large cylinder goes off
to the condenser; or an arrangement similar to the following may be adopted :-
Let only the bottom part of the smaller cylinder have a communication with

page_text: the boiler, and let there also be a communication between the bottom of the
smaller and the top of the larger cylinder, and another communication between
the top part of both cylinders, which last mentioned communication always
remains open, and let the top and bottom of the large cylinder also communicate
by means of a side pipe, and let the bottom part of the large cylinder communicate
with a condenser. Things being thus arranged, when steam is admitting into
the lower part of the smaller cylinder the piston in that cylinder will ascend, the
communication between the top of the two cylinders being then open, to allow the
steam above the smaller piston to pass into the top of the larger, where it is not to
be detained, but, along with the steam above the piston in the larger cylinder,
to be allowed to pass under the last-mentioned piston (which is now ascending
as well as the piston in the smaller cylinder), the communication between the
two sides of the large piston being now open, and the communication with the
condenser shut off. Both pistons having reached the top of their respective
cylinders, the communications which before were open must now be shut (ex-
cepting the communication between the two cylinders at their upper part), and
the communications between the bottom of the small and the top of the large,
and between the bottom of the large and the condenser, must be opened; the
steam last admitted into the lower part of the smaller cylinder will now ascend
into the top of the larger, and expand itself, following the piston of the larger
cylinder, which is now descending, its other side being open to the condenser,
and (as the tops of the two cylinders communicate) steam will pass into the
top of the smaller cylinder above its piston, so that both pistons descend to-
gether to the bottom of their respective cylinders, when a fresh charge of steam
is again to be admitted for a fresh stroke of the engine.
Fourthly. If my improvements be applied to one of the engines known by
the name of Watt's double engine, the working cylinder must have no direct
communication with the boiler, but must be made to communicate at its top
and bottom alternately with the lower and upper part of the smaller added
cylinder, or simply, as the case may be, at its top and bottom with the steani
measure, which has a direct communication with the boiler, the effect of which
must be sufficiently obvious from the details I have already given respecting
the nature of my Invention, and the way in which the same is to be carried
into actual practice.
Fifthly. With regard to steam engines in which the separate steam measure
may not be thought adviseable, the same may be improved by the application of
my aforesaid discovery, by making the boiler and the steam case or cases in
which the working cylinder or cylinders is or are inclosed much stronger than
usual, and by altering the structure and dimensions of the cocks, valves, slides,

page_text: or other means of admitting steam from the boiler into the cylinder or cylinders
in such a manner as that the steam may be admitted very gradually by a pro-
gressive enlargement of the aperture, so as at first to wiredraw and afterwards
admit more freely the same. The reason for this precaution is this,―steam of
such great elastic force as I employ, if admitted suddenly into the cylinder or
cylinders, when more than one working cylinder is employed, would strike with
a force that would endanger the safety and durability of the engine. The
aperture allowed to the valve, cock, or other contrivance, for admitting steam
into the cylinder or cylinders should be regulated by the following considera-
tion:-If the intention is that the engine shall work only, or almost wholly, by
condensation, the steam, in passing into the cylinder or cylinders, should be
forced to wiredraw itself, as I have already said, but so that the piston or
pistons may perform the whole or a great part of the stroke by the time the
intended quantity of steam has been admitted into the cylinder or cylinders;
for example, when steam of forty pounds the square inch is used, such a quan-
tity of the same as shall be equal in volume to one fortieth of the capacity of
the cylinder or cylinders, and so in proportion when steam of any other force
is employed, and when the requisite quantity has been admitted the steam is to
be shut off till the proper moment for admitting a fresh quantity; but if it is
intended that advantage shall also be taken of the elastic force of the steam
acting on one side of the piston or pistons while condensation goes on the
other side, then the steam must be admitted more freely, but still with caution
at the first, for the reason already mentioned. And in this, as well as in every
other application of my said improvenients, grounded on my said discovery of
the law of the expansibility of steam, due and effectual means must be used
to keep up the requisite temperature of all the parts of the apparatus into
which the steam is admitted, and in which it is not intended to be condensed.
And here it may be proper to state, that instead of the obvious and usual
means for accomplishing this, namely, inclosing them in the boiler, or in a
steam case or cases communicating with the boiler, the following method may
sometimes be used with advantage, viz, a separate fire under the steam case
or cases, which in that event will become a boiler or boilers, and must be fur-
nished with a safety valve or valves to regulate the temperature. By means
of the last mentioned arrangement, the steam from the smaller cylinder or
steam measure (when either of these are employed) may be admitted into the
larger cylinder or cylinders, kept at a higher temperature than the smaller, by
which its power to expand itself may be increased; and on the contrary, by
keeping the larger at a lower temperature than the smaller its expansibility

page_text: will be lessened, which, on particular occasions, and for particular purposes,
may be desirable. In every case care must be taken that the boiler, the case
or cases in which the cylinder or cylinders is or are enclosed, the steam pipes,
and generally all the parts exposed to the action of the expansive force of the
steam be of a strength proportioned to the high pressure to which they are
to be exposed.
With regard to the due degrees of strength of the parts of all my said
improvements, together with the nature of the materials and the proportions
of the same, except as herein described, I forbear any farther description, on
account of the numerous variations to which the same must be subjected, and
because every engineer of sufficient skill to be employed in works of this
nature will, without difficulty, arrange and determine the same, according to
the nature of the case.
Lastly, I have to observe that, to avoid unnecessary tautologics in speaking
of the proportion that ought to subsist between the smaller cylinder or the
steam incasure and the larger cylinder, or of the quantity of steam to be
admitted to the working cylinder, where a separate smaller cylinder or steam
measure is not adopted, though I have mentioned the regular proportions, as,
for example, of a measure or quantity equal to one fortieth of the working
cylinder, when steam of forty pounds the square inch is to be employed, or
equal to one thirtieth, or one twentieth when steam of thirty or of twenty
pounds the square inch is to be used, yet the only proportions that may be
used, for, though it may not be adviseable that the proportion of the smaller
cylinder or steam measure should in any case be made much smaller than I
have stated, yet in making it larger considerable latitude may be allowed; for
example, with steam of forty pounds the square inch, a smaller cylinder or
measure of one twentieth, or even larger, or of some intermediate proportion,
may be employed instead of one of a fortieth of the capacity of the larger or
working cylinder, and so with steam of any other given strength; and it may
be advisable that in a number of engines this should be the case, because of
the difficulty of preventing some waste of steam or partial condensation, which
might lessen the rate of working, if not allowed for in the size of the smaller
cylinder or steam measure, or in the quantity of steam admitted directly from
the boiler into the working cylinder where no smaller cylinder or steam
measure is employed; and in every case the engine, when got ready for work,
whatever may be the proportion that has been adopted as intended to be worked
with, should have its power tried by altering the load on the valve that ascer-
tains the force of the steam, in order that the strength of steam best adapted

page_text: for the engine may be ascertained, for it may turn out to be advantageous that
the steam should be employed in particular engines of an elastic force some-
what over or under what was first intended.
In witness whereof, I, the said Arthur Woolf, have hereunto set my
hand and seal, the Seventh day of July, in the year of our Lord
One thousand cight hundred and four.
Inrolled the same Seventh day of July, in the year above written.