CERTAIN IMPROVEMENTS IN AIR ENGINES
Year: 1840

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME; We; JAMES
STIRLING, of Dundee, Engineer, and the Reverend ROBERT STIRLING; D.D., of
Galston, Ayrshire, send greeting.
WHEREAS Her, present most Excellent Majesty Queen Victoria, by Her
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the First day of October; in the fourth year-of-Her reign, did, for
Herself, Her leirs and successors, give and grant unto us, the said James
Stirling and Robert Stirling, fer especial licence, full power, sole privilege
and authority, that we, the said James Stirling and Robert Stirling; our exors,
admors, and assigns, or such otliers as we, the said James Stirling and Robert
Stirling, our exors, admors, or assigns, "should at any time agree with, and no
others, from time to time and at all times during the terur of year therein
expressed, should and lawfully, might make, use, exercise, and vend, within
England, Wales, and the Town of Berwick-upon-Tweed; our Invention of
"CERTAIN IMPROVEMENTS IN AIR ENGINES" in which said Letters -Patent is
contained a proviso that we, the said James. Stirling and Robert Stirling, or
one of us, shall cause a particulardescription of the nature of our said-Invention
and in what manner the same is to be performed, to be enrolled in Her said
Majesty's High Court of Chancery within six calendar months next and
immediately after the date of the said in part recited Letters. Patent, as
in and by the same, reference being thereunto had, will more fully and at
large appear...
the said
NOW KNOW YE, that in compliance with the said proviso, we,
James Stirling and Robert Stirling, do hereby declare the nature of our said

page_text: Invention, and the manner in which the same is to be performed, are fully
described and ascertained in and by the following statement thereof, reference
being had to the Drawings hereunto annexed, and to the figures and letters
marked thereon (that is to say) :-
11
Figure 1, which is drawn to a scale of two inches to the foot, represents a
vertical section of the principal parts of our Invention. A, A, B, B, C, is the
air-vessel formed of the best cast iron, and connected by the port D, and the
pipe D, E, with the top of a cylindrical vessel F, F, G, G, H, also of cast
iron, called the plate box. The lower part of the air-vessel also communicates
with the plate box by means of three or more parallel pipes, of which one is
represented by H, 1. These pipes at their entrance into the air-vessel have
their mouths widened downwards and laterally, and covered by the fan-shaped
plate I, i, which is intended to spread the air with great velocity over the
whole extent of the spheroidal bottom. The part of the air-vessel A, A, B, B,
is accurately bored, the whole of the flanches are turned or planed, a copper
or iron wire is interposed at the joints B, B, and G, G, and a small strip or
wire of lead at all the other joints to render them air-tight; and the whole is
strongly bolted together; and being calculated to support one thousand pounds
is proved by a water pressure from within of seven hundred pounds upon the
square inch. In order to insure the tightness of the joints at B, B, and G, G,
we form those joints in the manner represented at Figure 11., and place a
quantity of soft solder or still more fusible metal A in contact with the inner
side of the wire a, so that when the engine is heated, the solder melts, and
prevents the air from escaping. K, K, L, L, is another air-tight vessel of
cast iron, which we call the driver, occupying generally about five-sixths of the
air-vessel. In order to prevent the heat from rising upwards, the driver has a
plate of cast iron fixed to its bottom-on the outside, a quantity of pounded
Bricks, or other imperfectly conducting substance, introduced into its lower
part, and the remainder divided into twelve or sixteen compartments by thin
plates of iron kept at equal distances from one another. The driver is made
to fit the bored part of-the-air-vessel, so as to be easily moved, and at the
same time to permit as little air as possible to pass by its sides;-and-its-top
and bottom are likewise formed to fit the top and bottom of the air-vessel. It
is moved by a turned and polished rod M, M, working through a leather collar,
which is made bywettingand pressingin a mould into the form represented atA,
Figure 11, and cut for use, as represented at B. This collar is fixed upon the
top of the air-vessel, into which also a pipe d,d, is soldered, which descends into
a vessel of oil e, e, so as to prevent the air from getting access to the collar, and
thus to keep it air-tight. Two-thirds of the plate box, reckoning from the

page_text: bottom H, are filled with plates of sheet iron, the greater part of which are
about 1/4 of an inch in thickness, cleared of oxide by a diluted acid placed per-
pendicularly and kept at a distance of '/o of an inch from one another by small
ridges or dimples, as represented at A, Figure IV. These plates are commonly
divided into four or more portions to diminish their effect in conducting heat
from the hot to the cold part of the plate box, and we sometimes make the
lowest portion of cast iron one sixth of an inch thick, and kept at a distance
of one twenty-fourth from one another by small ridges cast upon the one side,
and we make the highest portion of copper of the same thickness and distance
as the sheet iron plates. The remainder of the plate box is occupied partly by
a cooling apparatus to be presently described, and partly by blocks of iron,
glass, or other bodies perfectly solid, which accurately fill up all the remaining
space except what is necessary for giving the air free access to the plates and
pipes. The cooling apparatus consists of a great number of copper pipes six
and three-quarter inches long, and about one-eighth of an inch in diameter
within, and one-fourth without. These pipes are arranged in twenty-seven
horizontal rows, of which each alternate row has one pipe less than the rows
above and beneath it, in order that its pipes may be placed opposite to the
interstices of those rows. The pipes are kept at a distance of one twentieth
of an inch from one another in every direction, being soldered into two plates
of brass, A, A, A, A, Figure VII. Two other plates of brass, B, B, B, B, are
then soldered to the former at all their fourmargins, havinghorizontal passages
a, a, a, b, b, b, for connecting the ends of the pipes and returning the water
from the one end to the other, and having larger passages C and D, for intro-
ducing and taking off the water by the main pipes E and F. The main pipes
pass through holes in the cover of the plate box, and are made tight by
rings of lead screwed firmly into the joints, and the whole apparatus must be
able to resist an external pressure of four hundred pounds upon the square
inch. The application and use of all the contrivances which have now been
described is after this manner. The spheroidal part of the air-vessel, the
pipes H, I, and the bottom of the plate box are heated till the soot is burned
off, and the coal smoke ceases to adhere to them. This is done by a fire
placed beneath them, and the flues of the furnace are made to ascend about
When the whole appa-
ten inches upon the cylindrical part of the air-vessel.
ratus is thus brought to itsproper temperature, if the driver be movedupwards,
it must diminish the space A, K, at the top, and enlarge the space L, C, L, at
the bottom by an equal quantity. A portion of air is thus made to pass down-
wards through the plate box into the hot part of the air-vessel, and being thus
heated and expanded it is more than sufficient to occupy the whole increase of

page_text: space produced at the bottom by the motion of the driver, and the surplus
must be forced outwards at the port Q. On the contrary, when the driver is
moved downwards, a quantity of air is made to ascend through the plate box
and cooling apparatus, and being thus cooled and contracted it is not sufficient
to fill the increased space produced at the top, and a quantity of air must.enter
by the port Q to restore the equilibrium. Two of these air-vessels, therefore,
A, A, B, B, Figure V., which is drawn to a scale of half an inch to the foots
are connected with the opposite ends of a cylinder C,C,provided with a proper
piston and piston rod; which latter works through a leather collar, and, is con
nected with a crank D, and fly wheel E, E, E, which receive the impulse
communicated to the piston bythe expansion andcontraction of the air already
described. We make the capacity of the cylinder, exclusive of the space
occupied by the piston, about seventh tenths of the space left at the top of the
air-vessel when the driver is resting on the bottom. Another crank F, upon
the same shaft or axle with the fly, is connected to the drivers by means of
the rod G, G, the levers H, H, and I, I, and the side rods K, I, K,
so that the revolution of the fly and crank cause the drivers to rise and fall
alternately. The cranks are so adjusted upon the fly shaft, that from the
point where the motion of the drivers is reversed to that where the conse-
quent motion of the piston is reversed, the fly must revolve through an
angle of about seventy-five degrees of a circle. We also connect with the
said fly wheel an air pump L, L, whose piston is made, air-tight, by two
pieces of leather of the form represented at C, Figure III., and whose piston
rod works through a leather collar. The air-pump is."/12 of the diameter of the
cylinder, and is kept cool by a casing filled with cold water to prevent the
leathers from being damaged by heat. A communication is made from the
air-pump to both-ends- of the cylinder by means of a copper pipe and well
ground self-acting valves a, a, a, a, and we surround-the-copper pipes with
cold water, and let out the water which collects within it at the extremity.
The air-pump is intended to supply the waste of air by leakage, and likewise
to fill a reservoir-or-magazine of condensed air for starting the enginewith full
power; and we commonly, employ a pressure of air in-the-air-vessels of about
one hundred and fifty pounds upon the square inch when, not heated, but this
may be varied. The engine is started by detaching the drivers. and moving
them by the hand with the lever El, H, in the same manner as the valves of a
steam engine. A stop-cock.or-valve is also used to establish a communication
between the air-vessels and equalize their pressure before starting. We some-
times construct the air-vessels anddrivers in the formrepresented in Figure VI.,
which is a vertical section upon a scale of two inches to the foot... The air-

page_text: vessel A, A, A, A, has its cylindrical part accurately bored, its, junction
with the cover B, B, B, B, is made air-tight by interposing a strip of lead
between the flanches and strongly bolting them together, and the whole is
proved byan internalwater pressure of seven hundred pounds upon the square
inch. The driver consists of an outer shell or cap of cast iron a, a, b, b,
accurately turned and fitted to the air vessel as before specified, and having its
bottomperforated bya number of holes, whose collective areas should be about
one-twelfth of the area of the piston, and which are intended for the passage
of air; upon the bottom of this shell rests a piece of cast iron also perforated
with many holes, communicating with those already mentioned, and of equal
area. This piece of cast iron has small ridges upon its upper surface to support
the plates and facilitate the distribution of the air into the plates. These
consist of alternate sheets of plain and fluted glass which accurately fill
up the internal space D, D, C, C, and which should be divided into narrow
strips not exceeding one inch in breadth, as represented in the Figure, to
prevent their cracking by unequal expansion. The edges of the fluted glass
preserve passages for the air between the adjacent plates, and they ought to be
selected or made on purpose, so that the width of the passages may not exceed
one-sixtieth of an inch. At a small distance above these plates is the cover or
head of the driver E, E, which is perforated with a multitude of small holes
for the transmission of the air, and which is united to the outer shell already
described by a ring or cylinder of sheet iron extending from 6 to E, and
rivitted or screwed to both. The outer portion of the driver F, F, F, F, is
closely packed with plates of plain glass or iron to obstruct the passage of heat
from the air-vessel into the driver and into the space E, B, B, E. From the
centre, of the driver a turned and polished rod G, G, ascends through the cover
of the air vessel, and is kept tight by a leather collar and pipe dipping into a
vessel of oil, as already mentioned in the description of Figure L. The cooling
apparatus H, I, H, I, consists of a number of concentric plates or rings kept
at a distance of one-thirtieth of an inch from one another, and from the
cylindric part of the cover B,B,by small slips of flattened wire placed perpen-
dicularly between them, and thus furnishing perpendicular passages for the air
in the intervals between the plates. Figure VIII. represents the internal.com-
struction of one of these rings. It consists of two sheets of copper or brass
formed into cylinders with hard solder, and hammered nearly to the shape and
size required. The inner sheet is about one-fourth of an inch in thickness at
the margins A, A, B, B, when finished, and is turned into thirty-six grooves
one-sixth of an inch in width and depth. Small portions of the intervening
ridges are cut out-in the manner represented at C, C, C; and the outer sheet

page_text: D, D, D, D, which is one-twelfth of an inch in thickness, when fitted and
finished by turning or otherwise, is slipped on and soldered to the broad
margins of the inner sheet. The openings E and F are then cut, and the plate
is proved to be air-tight by an external pressure of four hundred pounds on
the square inch. The whole plates are then placed in the position already
mentioned and strongly soldered together around the openings E and F, and
the main pipes are soldered in so that the one may communicate with the three
uppermost, and the other with the three lowest grooves of all the plates. The
openings E and F are made narrower in each successive plate as they recede
from the main pipe, so as just to admit the necessary supply of water, by which
means the outermost plate being supported from within is enabled to sustain
the necessary pressure of four hundred pounds on the inch. A stream of cold
water is admitted through the main pipe which is connected with the three
lowest grooves of each cooling plate, and passing round both on the right and
left to the opposite side of the circle is made to pass upwards through a set of
small openings like those at C, C, into the three grooves next in order, by
which it is conveyed back to the sidewhere it entered. It again passes upwards
by the opening at Cinto the next three grooves, and thus going and returning
in a horizontal direction, and ascending by successive steps, it issues at last
through the other main pipe, carrying along with it the waste heat. The main
pipes ascend through holes in the cover of the air-vessel, and two or three
sheets of iron are fixed upon the outside of the exterior cooling plate to
intercept the radiant heat from the interior surface of the air-vessel. There is
a passage along the upper edges of the plates, diminishing in width from K to
K, Figure VI., for the purpose of conveying the air from the cylinder to the
cooling plates. Instead of the alternate plates of plain and fluted glass, we
sometimes employcylindrical rods_of_glass tapering at the lower ends, of equal
diameter, which should not exceed one-sixth of an inch, and packed as
close as their circular form will admit. In order to support these rods,
which are placed perpendicularly, we employ a number of cast iron
plate one-fourth of an inch thick, and distant from one another, placed,
perpendicularly, having their upper edges in one plane, and their under-
edges adapted to the bottom of the driver. Note.-We sometimes use glass
rods or alternate plate of plain and fluted glass, instead of iron in the
plate box represented in Figure I., in which case we enlarge said plate
box, or diminish the thickness of the rods or plates, so as to admit about
three times as much surface of glass as of iron to be exposed to the current of
air, and we do not divide the plates or rods of glass into several portions, they
having less tendency to conduct the heat, Farther; we observe the following

page_text: rules in the construction of our improvements upon air engines:-First, in
order to enable the air to assume almost instantaneously the temperature of
the successive points of the plates with which it is brought into contact, we
make the distances of those plates very small, that is to say, in iron plates we
make the distances not more than one-fiftieth, and in glass plates not more
than one-sixtieth of an inch. Second, in order to enable the plates to give out
or take in the necessary quantity of heat in the time occupied by one stroke of
the driver, we allow in iron and copper plates twenty square inches of surface,
and in glass rods or plates sixty square inches to be exposed to the air for
every cubic inch of space contained in the interval between the air-vessel and
driver. When a minimum pressure of more than one hundred and fifty pounds
on the inch is used, we encrease the extent of surface nearly in the same pro-
portion. Third, as every portion of space within the air-vessel, cylinder, plate
box, and passages takes in a quantity of air when the pressure is increased, and
gives out a quantity when the pressure is diminished, so as to impair the
impulse given to the piston, we carefullyguard against all unnecessary.space in
the interior of the engine, and in particular we make the passages as narrow as
. is consistent with the easy motion of the air. Fourth, for the reason just
stated, as well as to proportion the surface acted on by the fire to the quantity
of air employed, when we have occasion to make a larger engine than that
represented in the Drawings annexed to this Specification, we enlarge the
diameter of the air-vessel and plate boxes rather than encrease their length,
and we multiply the pipes which connect the bottoms of the air-vessel and
plate boxes.
We sometimes also connect two or more air-vessels with each
end of the cylinder, instead of one of a larger size.
Having thus described the nature of our Invention, and the manner of per-
forming the same, we would have it understood thatwe do not confine ourselves
to the precise arrangements shewn and described, provided the general cha-
racters of our Invention be retained. Neither dowe claim under Her Majesty's
Letters Patent the exclusive use of all the things we have described with a
view to render our Invention intelligible, as many of them have already been
made and used by ourselves and others for similar purposes. But we do claim
the following improvements upon air engines already more fully described:-
First, the employment of strips or rods of glass for receiving and imparting
heat during the passage of the air from the hot to the cold chamber, and vice
versa.
Second, the formation of the glass, iron, or other materials employed for this
purpose into continuous plates, strips, or rods of considerable length, having
their contiguous surfaces so placed as to make all the passages for the air

page_text: narrow, and in a line parallel or nearly so with the axis of the plate box
(Figure 1.) or the driver (Figure VI). By this means we inake the motion of
the air more easy, we heat and cool it more perfectly, and economise heat.
Third, the mode of constructing air engines, whereby we cause the air in
passing from the heated end of the air-vessel to the cool end thereof, to pass
first amongst an extensive system of surfaces to give off heat thereto, and then
to pass amongst an extensive cooling apparatus cooled by the passage of fluid,
and whereby we cause the air in returning from the cool end of the air-vessel
to the heated end thereof to pass back through the same extended system of
surfaces, and having taken up much heat from those surfaces to pass into the
heated end of the air-vessel; at the same time we would have it understood
that we do not claim the employing of an extended system of surfaces alter-
nately to take up heal from and give off heat to the air of air engines when
separately.considered; neither do we claim the passing of the air or air engines
through a cooling apparatus cooled by water or other fluids, when separately
considered; but this part of our Invention relates to the combined using of
such apparatus as above described.
Fourth, the-use or application in air engines of cupped-leather collars around
the piston rods or other rods which communicate with the interior of the
engine, by which means we ar enabled to fine air at a higlier pressure.
In witness whereof, I, the said James Stirling, have hereunto set my
hand and seal, this Twenty-sixth day of March, in the year of our
Lord One thousand eight hundred and forty-one