IMPROVEMENTS IN HOT AIR ENGINES
Year: 1859

page_text: LETTERS PATENT to Jean Baptiste Pascal, of Paris, in the Empire of
France, Civil Engineer, for the Invention of "IMPROVEMENTS IN HOT AIR
ENGINES."
Sealed the 15th November 1859, and dated the 2nd June 1859.
PROVISIONAL SPECIFICATION left by the said Jean Baptiste Pascal
at the Office of the Commissioners of Patents, with his Petition, on
the 2nd June 1859.
I, JEAN BAPTISTE PASCAL, of Paris, in the Empire of France, Civil
Engineer, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN HOT AIR ENGINES," to be as follows:-
My Invention consists in improvements in generators and hot air engines,
employing air at the pressure of the atmosphere, or air more or less com-
pressed, which improvements I combine so as to constitute an improved hot
air engine.
This improved engine is composed of three distinct parts, viz., first, the
generator; secondly, the machine or reciever; and, thirdly, the reservoir of
compressed air, when such is used. 1stly, the generator is of a kind known
under the name of piston generators, which alternately heat the air in its
passage to act upon the piston, and cool that which has served for that
purpose. The generator comprises the particular arrangements forming the
first part of my Invention. 2ndly, the machine or reciever consists of a
piston moving in a cylinder, and furnished according to the peculiar arrange-

page_text: ments forming the second part of my Invention. 3rdly, the reservoir of
compressed air, when the apparatus is actuated by compressed and heated
air, forming the peculiar arrangements which form the third part of my
Invention.
These improved apparatus are represented in the Drawing hereunto
annexed, in which Fig. 1 represents a central vertical section of, 1st, the
reservoir; 2nd, a primary generator; 3rd, a double-action reservoir; and
4th, a second generator, which is similar to the first one, seen in elevation.
Fig. 2 shows a plan of the whole apparatus. In these two Figures similar
letters of reference indicate like parts where they recur.
In the Drawings
those parts are omitted which are sufficiently well known to require no
description.
In the first place I will describe one of the generators, the other one
being similar in every part. a, furnace, of circular or other form, fitted in
masonry, and furnished with a casing of sheet' iron, having fire bars, a door
for supplying the fuel, and an ash-pit, &c., as usual; b, circular flues for the
escape of the products of combustion; c, openings made in the horizontal parts
of the circular flues. The surfaces of these openings gradually diminish from
right to left, for the purpose of obliging the products of combustion to spread
equally throughout all parts of the circular flues b, so as to equalize the
distribution of the caloric throughout the surface of the furnace; d, escape
for the smoke; e, heating surface of the air engine; this surface, which is
supported above the furnace, is formed of a diaphragm of cast iron of con-
siderable thickness at its centre, and gradually diminishing in thickness
towards the circumference, for the purpose of presenting to the furnace a
considerable mass of metal, which constantly takes up the greatest quantity of
heat disengaged, and also to enable it to be submitted to the action of a highly
heated furnace, which surface may be raised to a high temperature without
any fear of damage or rupture, or by partial dilatation. A similar result may
be obtained, but with fewer advantages, by using a disc of considerable thick-
ness equal throughout its surface. This heating surface forms a base, as easily
understood, which, by reason of the facility of changing its position if required,
permits of the apparatus being removed at a small cost. f, body of the
generator, formed of a cast-iron cylinder fitted in masonry, stayed in the upper
part by an arm of wrought iron; 9, passage for air, which has acted on or is
to act on the piston. The passage g¹ of the left-hand generator communicates
above the said piston; h, deflector, consisting, 1st, of a mass of cast iron i, the
form of the under surface of which depends upon that of the upper surface of
the part e; this mass of metal absorbing the rays of heat emitted from the

page_text: base e, and reflecting them in turn, causes the film of air serving as the motor
to be quickly heated between the two sources, both of great heat. 2ndly, of a
layer of masonry or fire-clay, for intercepting the passage of the heat emitted
by plate i. 3rdly, of two plates k, superposed & united together in such
manner that in two of the spaces a current of cold water constantly circulates.
The three parts last herein-before described are solidly fixed together and
form the piston, which moves in the body of the generator without touching
the sides, so as to leave a passage for the displacement of the air; 1, hollow
rod of the piston, serving to set it in motion, and at the same time to allow the
passage at the inlet and outlet of the refrigerating water, for which purpose it
is divided by the central partition forming two channels, one for the inlet and
the other for the outlet of the water; m, flexible tube for the supply of water,
opening into the inlet channel. This tube conducts the cold water either
directly from the pump, which is worked by the machine, or from an inter-
mediate reservoir; n, exit pipe communicating with the exit channel of the
piston rod for distributing the water on to a cover, herein-after described;
o, hollow cover, formed of thin plate with and having on its surface strong
ribs; at the centre of this cover is a stuffing box, through which the rod of
the piston of the generator passes; on its periphery there is a rim for holding
the water, which covers it; this cover is also furnished at the upper part with
a distributor.
I will now proceed to describe the machine or reciever-p, support, on
which the machine rests; 7, setting of masonry furnished with a casing of
sheet iron; d, extension of the smoke passage from the generators, extending
beyond and affording passage for the smoke, which is to repeat the base and
sides of the motive cylinder before passing to machinery 7, as herein-before
described. The smoke arrives at the chimney after having passed through
openings similar to openings c, and diminishing in section in the same
manner and for a similar purpose; s, double-action motive cylinder; the
bottom of this cylinder, like the base e of the generator, is of greater thickness
towards the centre for the purpose before mentioned. This bottom may be
also united to the other parts to render it easier of construction and for repairs.
If required, this cylinder may recieve the direct action of a suplemental
furnace. t, pipes, for the passage of the air to act on, or which as acted
upon the motive piston; these pipes are connected to pipe 9 from each of the
generators; u, motive piston of cast iron or bronze (by preference of bronze),
of cylindrical form, slightly conical on its exterior towards the bottom, of
sufficient thickness for transmitting to the heated air introduced above the
piston, a part of the caloric which it recieves by radiation from the bottom of

page_text: cylinders; it is further furnished with segments and a rod for the transmission
of motion; x, cover of the cylinder fitted into the empty space of the body
of the piston, so as to leave as little space as possible for the concentration
of caloric from the heated air; it is fitted with a long stuffing box, through
which the piston rod passes, as seen in the Drawing. y, tubes furnished with
caps, which communicate with the pipes t & g, from either side. In each
of these caps a valve works; communicating with the reservoir of com-
pressed air, as I will now proceed to describe :-These valves conduct the
'necessary quantity of air into the cold part of the generators, for re-establishing
'the initial pressure, which is diminished by reason of escapes. a¹, tube, in con-
nection with the outer tube z, for conducting the compressed air into the
reservoir. This compression is effected by a small pump actuated by the
machine. This air is intended to make up for any escape, and by this means
to maintain a constant and uniform pressure in the reservoir and in the appa-
ratus. ¹, escape valve for the air which may arrive in excess in the reservoir,
and which would thus raise the pressure above the desired limit. The amount
of pressure at which to work is regulated by means of a lever arm attached.
c, screw plug actuated by a fly wheel for preventing the exit of air; d', air
passage extended to the interior of the reservoir; e¹, capacity forming an
interior lining of thin metal, either of copper or lead, closed at the upper part
by a dome. This capacity should be perfectly air-tight; d, exterior casing
surrounding the lining e¹. Between the inner and outer casings is an annular
space, which is filled with water supplied from below by pressure; f, disc, on
which the casing e¹ rests, to which the casing de is fixed hermetically. When
pressure is established in the reservoir, the water which is at the bottom is
forced, as above described, into the annular space, where it replaces the air
which has found an exit at the rivets and other escapes in the casing ds; this
lining of water thus establishes round the interior of this reservoir an bydraulic
casing, which renders all escape impossible, and also permits of the preservation
of compressed air for an indefinite length of time when the plug c¹ is herme-
tically closed.
.
Supposing the apparatus arranged as indicated on the Drawing, and
provided with air, condensing water, and a fire; and, in the second place, the
reservoir containing the required amount of air; and, thirdly, the piston on
the right to be in its highest position, and that on the left in its lowest position;
and, lastly, supposing the shaft moved by the machine and communicating to
the two pistons a reverse movement, which causes them to act in such way that
one descends while the other ascends; in opening the plug c¹, the compressed
air of the reservoir is introduced into the generating apparatus and in the

page_text: motive cylinder, after having raised the clacks which it meets in its passage.
If the two pistons are oscillated by hand, that is to say, simply changed in
their respective positions by means of connecting gear which unites them
(particular gear for balancing the pistons). In the left generator the air
which remains above the piston of the cold part, underneath and over the
heating surface where it dilates, and from thence acts on the piston to cause
it to descend. While the balancing movement is being effected, the air which
occupies the lower part of the right-hand generator is also displaced and passed
into the upper part, where it diminishes in volume and pressure. The descent
of the right piston, like that of the left, is controlled by the machine, and
causes the air, which was at the upper part, to become heated at the lower
part, and to dilate itself; and, lastly, to act on the piston for the purpose of
raising it again. The other piston, as above mentioned, is also controlled by
the same means, and lowered by the movement of the machine; the air is
dilated, which has acted on the piston, and is condensed at the cold part, and
thus, when once in operation, the apparatus continues its movements, that is to
say, the right generator raises the piston, and then the left-hand generator
lowers it. The reservoir of compressed air is constantly in connection with
the generators when it happens that, in consequence of escape, the condensed
air in the cooling part is no longer at the initial pressure, the clack valves
open, and afford passage to the air from the reservoir, which re-establishes that
pressure.
Observations. The capacity which remains free in the generating cylinder
should be at least equal to that of the motive cylinder, and the diameter of
the generating cylinder should be increased as much as possible in relation to
the stroke; and the movement of the air-driving piston of the generator
should be effected during the time that the motive piston traverses a fourth
part of its course.
.
It has been seen that to set the machine in motion, the two air pistons of
the generators require to be changed by hand but once. To stop the machine
a valve may be made use of which would intercept the entry of the air to the
cylinder; but it is more convenient to disengage the parts which connect the
two pistons of the generators. To moderate the motion of the machine a valve
can be made use of, which retards the entry of the warm air to the cylinder,
which I think it best to diminish by a suitable arrangement, the course of the
generator pistons, especially for large machines. To change the action of the
machine, the organs transmitting. the movement to the generator pistons should
be reversed.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Jean Baptiste Pascal in the Great Seal Patent Office on
the 28th November 1859.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JEAN
BAPTISTE PASCAL, of Paris, in the Empire of France, Civil Engineer, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Second day of June, in the year of our Lord
One thousand eight hundred and fifty-nine, in the twenty-second year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Jean Baptiste Pascal, Her special licence that I, the said Jean
Baptiste Pascal, my executors, administrators, and assigns, or such others
as I, the said Jean Baptiste Pascal, my executors,. administrators, and
assigns, should at any time agree with, and no others, from time to time and
at all times thereafter during the term therein expressed, should and lawfully
might make, use, exercise, and vend, within the United Kingdom of Great
Britain and Ireland, the Channel Islands, and Isle of Man, an Invention
for "IMPROVEMENTS IN HOT AIR ENGINES," upon the condition (amongst
others) that I, the said Jean Baptiste Pascal, my executors or adminis-
trators, by an instrument in writing under my, or their, or one of their
hands and seals, should particularly describe and ascertain the nature of
the said Invention, and in what manner the same was to be performed,
and cause the same to be filed in the Great Seal Patent Office within six
calendar months next and immediately after the date of the said Letters
Patent.
.
NOW KNOW YE, that I, the said Jean Baptiste Pascal, do hereby
declare the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by the
following statement, reference being had to the accompanying Drawings and
to the letters and figures marked thereon, that is to say:
My Invention consists of improvements in generators and hot air engines,
employing air at the pressure of the atmosphere, or air more or less com-
pressed, which improvements I combine so as to constitute an improved hot-
air engine.
This improved engine is composed of three distinct parts, viz. -1st., the
generator; 2ndly, the machine or receiver; and 3dly, the reservoir of com-
pressed air, when such is used. First, the generator is of the kind known
under the name of piston generators, which alternately heats the air in its

page_text: passage to act upon the piston, and cools that which has served for that
purpose; this generator comprises the particular arrangements forming the
first part of my Invention. Secondly, the machine or receiver consists of a
piston moving in a cylinder, and furnished according to the peculiar arrange-
ments forming the second part of my Invention. Thirdly, the reservoir of
compressed air when the apparatus is actuated by compressed and heated
air, forming the peculiar arrangements which form the third part of my
Invention.
These improved apparatus are represented in the Drawing hereunto annexed,
in which Fig. 1 represents a central vertical section of, 1st., the reservoir: ;
2dly, a primary generator; 3dly, a double-action receiver; and 4thly, a second
generator, which is similar to the first one seen in elevation. Fig. 2 shows a
plan of the whole apparatus. In these two Figures similar letters of reference
indicate like parts where they recur. In the Drawing those parts are omitted
which are sufficiently well known to require no description.
In the first place I will describe one of the generators, the other one being
similar in every part. a, furnace of circular or other form, fitted in masonry,
and furnished with a casing of sheet iron, having fire-bars, a door for supplying
the fuel, and an ash-pit, &c., as usual; b, circular flues for the escape of the
products of combustion; c, openings made in the upper horizontal parts of the
circular flues. The surface of these openings gradually diminish from right
to left, for the purpose of obliging the products of combustion to spread equally
throughout all parts of the circular flues b, so as to equalize the distribution of
the caloric throughout the surface of the furnace; d, escape for the smoke; e;
beating surface of the air engine. This surface, which is supported above the
furnace, is formed of a diaphragm of cast iron of considerable thickness at its
centre, and gradually diminishing in thickness towards the circumference, for
the purpose of presenting to the furnace a considerable mass of metal, which
constantly takes up the greatest quantity of heat disengaged, and also to
enable it to be submitted to the action of a highly heated furnace, which
surface may be raised to a high temperature without any fear of damage or
rupture or by partial dilatation. A similar result may be obtained, but with
fewer advantages, by using a disk of considerable thickness equal throughout
its surface. This heating surface forms a base, as easily understood, which, by
reason of the facility of changing its position if required, permits of the appa-
ratus being renewed at a small cost; f, body of the generator formed of a cast-
iron cylinder fitted in masonry, stayed at the upper part by an arm of wrought
iron; g, passage for the air which has acted on or is to act on the piston.
The passage g of the right-hand generator communicates below the piston, and

page_text: the passage 9 of the left-hand generator communicates above the said piston;
h, deflector, consisting first of a mass of cast iron i, the form of the under
surface of which depends upon that of the upper surface of the part e; this mass
of metal absorbing the rays of heat emitted from the base c, and reflecting them
in turn, causes the film of air serving as the motor to by quickly heated between
the two sources, both of great heat; secondly, of a layer of masonry or fire-clay
for intercepting the passage of the heat emitted by plate i; thirdly, of two
plates superposed and united together in such manner that in two of these
spaces a current of cold water constantly circulates. The three parts last
berein-before described are solidly fixed together and form the piston, which
moves in the body of the generator without touching the sides, so as to leave
a passage for the displacement of the air. 1, hollow rod of the piston, serving
to set it.in motion, and at the same time to allow the passage at the inlet and
outlet of the refrigerating water, for which purpose it is divided by a central
partition forming two channels, one for the inlet and the other for the outlet of
the water.
m, flexible tube for the supply of water opening into the inlet
channel; this tube conducts the cold water either directly from the pump which
is worked by the machine, or from an intermediate reservoir. n, exit pipe
communicating with the exit channel of the piston rod for. distributing the
water on to a cover herein-after .described. o, hollow cover formed of thin
plate, and having on the surface strong ribs; at the centre of this cover is a
stuffing box, through which the rod of the piston of the generator passes; on its
periphery there is a rim for holding the water which covers it; this cover is
also furnished at the upper part with a distributor.
I will now proceed to describe the machine or receiver. p, support on which
the machine rests; q, setting of masonry, furnished with a casing of sheet iron;
d, extension of the smoke passage for the generators, extending beyond and
affording passage for the smoke, which is to reheat the base and sides of the
motive cylinder before passing to the chimney, as herein-after described.
The smoke arrives in the chimney after passing, through openings u*, similar
to openings c, and diminishing. in section in the same manner and for a
similar purpose. . s, double-action motive cylinder; the ottom of this
cylinder, like the base e of the generator, is of greater thickness towards
the centre, for the purpose before mentioned. This bottom may be also
united to the other parts to render it easier of construction and repairs. If
required, this cylinder may receive the direct action of a supplemental furnace.
t, pipes for the passage of the air to act on or which has acted upon the
motive piston; these pipes are connected to pipes g from each of the gene-
rators. u, motive piston, of cast iron or bronze (by preference of bronze), of

page_text: cylindrical form, slightly conical on its interior towards the bottom, of sufficient
thickness for transmitting to the heated air introduced above the piston a part
of the caloric which it receives by radiation from the bottom of cylinders; it
is further furnished with segments and a rod for the transmission of motion.
x, cover of the cylinder fitting into the empty space of the body of the piston;
so as to leave as little space as possible for the concentration of caloric from
the heated air; it is fitted with a long stuffing box, through which the piston
rod passes, as seen in the Drawing. y, tubes furnished with caps, which
communicate with the pipes t and g from either side. In each of these caps
a valve works, communicating with the reservoir of compressed air, as I
will now proceed to describe. These valves conduct the necessary quantity of
air into the cold part of the generators for re-establishing the initial pressure,
which is diminished by reason of escapes. a', tube in connexion with the
other tubes, for conducting the compressed air into the reservoir. The
compression is effected by a small pump actuated by the machine. This air
is intended to make up for any escape, and by this means to maintain a con-
stant and uniform pressure in the reservoir and in the apparatus. ', escape
valve for the air which may arrive in excess in the reservoir, and which would
thus raise the pressure above the desired limit. The amount of pressure at
which to work is regulated by means of a lever arm attached. c', screw plug,
actuated by a fly wheel, for preventing the exit of air; d', air passage,
extending to the interior of the reservoir; e¹, capacity forming an interior
lining of thin metal, either of copper, lead, or other material closed at the
upper part by a dome; this capacity should be perfectly air-tight. d, exterior
casing surrounding the lining e. Between the inner and outer casings is an
annular space which is filled with water, supplied from below by pressure.
f, disk, on which the casing e rests, to which the casing d is fixed her-
metically. When the pressure is established in the reservoir, the water which
is at the bottom is forced, as above described, into the annular space, where it
replaces the air which has found an exit at the rivets and other escapes in
the casing d; this water, forming a lining, thus establishes round the interior
of this reservoir an hydraulic casing, which renders all escape impossible, and
also permits of the preservation of compressed air indefinitely when the
plug c is hermetically closed. Supposing the apparatus arranged as indicated
in the Drawing, and provided with air, condensing water, and a fire; and, in
the second place, the reservoir containing the required amount of air; and,
thirdly, the piston on the right to be in its highest position, and that on the
left in its lowest position; and, lastly, supposing the shaft moved by the

page_text: machine, and communicating to the two pistons a reverse movement, which
causes them to act in such a way that one descends while the other ascends;
in opening the plug c', the compressed air of the reservoir is introduced into
the generating apparatus and in the motive cylinder, after having raised the
clacks which it meets in its passage. If the two pistons are oscillated by
hand, that is to say, simply changed in their respective positions by means of
connecting gear, which unites them (particular gear for balancing the pistons)
in the left generator, the air which remains above the piston of the cold part
passes underneath and over the heating surface, where it dilates, and thence
acts on the piston, to cause it to descend. While the balancing movement is
being effected the air which occupies the lower part of the right-hand
generator is also displaced and passes into the upper part, where it diminishes
in volume and pressure. The descent of the right piston, like that of the
left, is controlled by the machine, and causes the air which was at the upper
part to become heated at the lower part, and to dilate itself, and, lastly, to
act on the piston [for the purpose of raising it again. The other piston, as
above mentioned, is also controlled by the same means, and lowered by the
movement of the machine. The air is dilated which has acted on the piston,
and is condensed at the cold part, and thus, when once in operation, the
apparatus continues its movement, that is to say, the right generator raises
the piston, and the left-hand generator lowers it. The reservoir of compressed
air is constantly in connection with the generators. When it happens that,
in consequence of escape, the condensed air in the cooling part is no longer
at the initial pressure, the clack valves open, and afford passage to the air
from the reservoir, which re-establishes that pressure.
Observations. The capacity which remains free in the generating cylinder
should be at least equal to that of the motive cylinder, and the diameter of the
generating cylinder should be augmented as much as possible with regard to
their course, and the movement of the air-driving piston of the generator
should be effected during the time that the motive piston traverses a fourth
part of its course.
It has been seen that to set the machine in motion the two air-driving
pistons of the generators require to be changed by hand but once. To stop the
machine a valve may be made use of which would intercept the entry of the
air to the cylinder, but it is more convenient to disengage the parts which con-
nect the two air-driving pistons of the generator. To moderate the motion of
the machine, a valve can be made use of which retards the entry of the warm
air to the cylinder, but I think it best to diminish by a suitable arrangement

page_text: the course of the generating pistons, especially for large machines. To change
the action of the machine, the organs transmitting the movement to the
generator pistons should be reversed.
Having thus described the nature and particulars of the said improvements
in hot-air engines, I desire it to be distinctly understood that I do not confine;
myself to the precise details herein described, as such may be varied or
modified without departing from the principle of action thereof; likewise I
do not confine myself to the strict figure or form of any apparatus or portions
of apparatus herein described; but I claim as new and of my Invention,―
First, the general arrangement of the apparatus as above described, and as
represented in the annexed Sheet of Drawings.
Second, the particular arrangements, 1st, of the bottom or diaphragm of the
generator, which bottom is of considerable thickness, diminishing from the
centre to the circumference, which enables its being submitted in a direct way
to the action of a highly heated furnace, and consequently to be raised to a
high temperature without any fear of damage or rupture, or by partial dilatation.
This bottom or diaphragm being a distinct piece can easily be constructed,
repaired, or changed. Instead of this decreasing thickness from the centre to
the circumference, which is indeed a rational application of an equal distribu-
tion of the heat, a disc of equal thickness throughout may, but with fewer
advantages, yield a similar result, provided that it presents a sufficient volume
for the absorption of the whole heat emitted by the fire-grate.
2dly, of the thick metal plate forming the lower part of the air-driving
pistons, which mass of metal absorbing the rays of heat emitted from the base e
of the generator, and reflecting them in turn, causes the film of air to be heated
between two sources, both of great heat.
3rdly, of the upper part k of the said piston, which is a cold part closed by
two plates, between which a current of cold water circulates. This cold part
is intended not only to shut out all portions of caloric arising from the lower
part, notwithstanding the want of conducting property of the fire-clay, but also
to join its refrigerating rays to those emitted by the water-closed lid of the
apparatus, and thereby increase the refrigerating power.
4thly, of the bottom of the motive cylinder, which for the like purpose is
similar to that of the generator.
5thly, of the hollow motive piston, and also of the lid which encloses it
during its stroke upwards, for the easier transmission of the heat from the
lower part to the upper part.
6thly, of the channels and openings and u leading the products of com-
bustion, and distributing them equally on their progress.

page_text: Third, I claim the direction imparted to the products of combustion of the
generator, which products after working within the generator go and heat
the motive cylinder.
Fourth, I claim the arrangement of the air reservoir, which by means of
the inside coating 1, and of the water which spreads itself into the annular
space, is rendered perfectly air-tight, so that when the orifice of the said
reservoir is closed by the plug c, compressed air can indefinitely be kept there-
unto. This air reservoir I claim as applicable also to other apparatus or
machines.
Fifth, and I claim the mode of distribution into the generator of the air
contained in the reservoir.
In witness whereof, I, the said Jean Baptiste Pascal, have hereunto
set my hand and seal, this Nineteenth day of November, One thousand
eight hundred and fifty-nine.
J. BT. PASCAL. (L.S.)