IMPROVEMENTS IN GAS AND AIR ENGINES
Year: 1853

page_text: LETTERS PATENT to Fabian Wrede, of Stockholm, in the Kingdom
of Sweden, for the Invention of "IMPROVEMENTS IN GAS AND AIR
ENGINES."
Sealed the 8th September 1853, and dated the 11th July 1858.
PROVISIONAL SPECIFICATION left by the said Fabian Wrede
at the Office of the Commissioners of Patents, with his Petition,
on the 11th July 1853.
I, FABIAN WREDE, of Stockholm, in the Kingdom of Sweden, do
hereby declare the nature of the said Invention for "IMPROVEMENTS IN
GAS AND AIR ENGINES" to be as follows:-
Under the denomination of the gas engine I understand an engine
which, for producing mechanical effect, employs the dilatation of per-
manent gases by heat, in accordance with following new principles,
videlicet:-
One and the same mass of gas is moved backwards and forwards
between two different rooms in such a manner that it does not undergo
any change in its volume through the transportation. During the
transport from the one room to the other it is alternately heated and

page_text: cooled, by which means its elasticity is alternately increased and
diminished. The mass of gas in question is in constant communication
with the one end of a common working cylinder, on whose piston it will
consequently exercise an alternately stronger and worker pressure, and
cause it to move backwards and forwards in the same manner as in steam
engines. The transport of the gas can be effected in two quite different
manners; videlicet, either A,) by moving the gas from one part, of a
closed vessel to another by means of a plunger, which fills up a great
part of its interior volumé, or B.) by expelling the gas from a cylin-
drical or prismatical vessel by means of a piston, letting it pass freely
through an exterior communication either to the other end of the same
vessel (videlicet, on the other side of the piston), or into another vessel
whose piston moves in such a manner that the gas will not undergo any
change in its volume through the transporting process.
The improvements which I have made in the gas engines refer
principally to the latter of the above-mentioned methods of moving
the gas, or that which is stated under B. In order to explain these
improvements, and show clearly the advantages gained by them, we
must first call to mind a distinguishing property in gases generally, that
of being extremely bad conductors of heat. In consequence of this
property it is evident that if a mass of heated gas could be moved
into a vessel of a lower temperature in such a manner that no motion
arose within the gas itself, then only the exterior parts of the mass, or
those which immediately touched the walls of the vessel, would be
cooled by them, while, on the contrary, the rest of the mass would
retain its higher temperature till the streams by degrees arising had
had time to develope themselves. If we now imagine, in accordance
with what has been above pointed out, that the gas by means of a piston
is forced out of the upper part of a generator,-by generator I mean
that vessel in which the movement of the gas, and consequently its
alternate heating and cooling, is produced,--and that by means of-an
exterior communication it is introduced into the lower part of the same
generator, it is evident that it must there flow in with a velocity
greater than that of the piston, in the same proportion as the area of
the latter is greater than the area of the opening of the pipe. It

page_text: must consequently reach the lower surface of the piston, spread itself
along it, and then descend along the walls of the generator, in conse-
quence of the sucking arising in the lower corners. It is consequently
evident that if the gas enters heated to a higher temperature than that
of the walls of the generator it must soon be cooled by them, so that
no advantage can be derived from the greater degree of heat. If, on
the other hand, instead of flowing in through a single opening at the
bottom of the generator, the gas is introduced through a great number
of small holes equally distributed over its whole surface the case will
be quite different. The greater velocity with which the gas even now
flows in through the small holes is soon neutralized by the sucking
arising between them; and the greater circulating motion, which in
the former case would put almost the whole mass of gas in contact
with the walls of the generator, will now be exchanged for a motion
of the gas which, on the whole, will be an even one, and conse-
quently only the outer part of the same come in contact with the
generator.
Those advantages which are gained by this arrangement can be
obtained in several different manners, of which I consider the following
the most simple and applicable: A, B, C, D, (Figure 1,) represents a
closed cylindrical generator, and E, F, G, H, another cylinder enclosed
in the same, the exterior diameter of which is so much less than the inuer
one of the former, that the space between them forms a sufficiently
spacious channel of communication between the upper and the lower
parts of the generator. The inner cylinder is closed with a lid at the
upper end, and one at the bottom supplied with a great number of
Smaller holes. When now the piston K, is raised the gas above it is
forced to rise through the holes in the upper lid E, F, in order after-
wards to descend through the space between the cylinders, and to enter
between the bottoms C, D, and G, H, and flow into the lower part of
the generator, through the holes in the inner bottom G, H. It comes
consequently into immediate contact with the two bottoms, which are
warmed by the furnace; and it must, therefore, on entering the gene-
rator, be nearly of the same temperature as they are, very little of which
will, according to what has been shewn, be lost during the motion in
the generator. When the piston is again lowered the gas goes in an

page_text: inverted order, and must then enter above the piston cooled by the
water introduced above the lid A, B.
As well through the alternate influence of the warm and cold gas
of the walls of the cylinders, as through their peculiar conducting
power, the walls will by degrees assume a state of temperature decreasing
from below upwards, by which means the heating and cooling of the
gas will be almost entirely effected in the space between them. That
the generator must be supplied with a side opening, through which it
stands in communication with the one end of a working cylinder in the
sanic manner as has before been pointed out, is of course taken for
granted.
When the heated gas rises from the warm to the cold end of the
generator through the space between the two cylinders intended for this
purpose it imparts a considerable portion of its heat to their walls, and
comes in between the two lids considerably cooled, on which account
only a small part of its original heat need be taken away by means of
the cooling water. The more completely this can be produced the
more advantageous it is, because the heat imparted in the first-
mentioned manner is not lost, but will in a very considerable degree
be again taken up when the cooled gas is again led back in the con-
trary direction.
In order to obtain this object it is necessary that the space between
the cylinders must be made as narrow as possible. As, however, this
space must form a sufficiently spacious communication between the two
ends of the generator, it cannot be diminished beyond a certain degree.
The greater the generator is, the wider must the space evidently be;
and in greater engines it should be so large that the stream of gas
flowing through it can but imperfectly impart its heat to the sur-
rounding walls, or receive it again from them. In order to avoid this
difficulty one can place between the two before-mentioned cylinders
one or more intermediate, by which means the stream of gas can be
divided into two or more, each of which can then receive the necessary
thinness. The Figure 2, shows a generator arranged in this manner.
The intermediate cylinder is in this Figure dividel lengthwise iuto two,
in order to form round the generator a sufficiently spacious communi-
cation with the working cylinder.

page_text: The advantages arising from the manner of moving the gas now de-
scribed, compared with the first-mentioned, are now evident. It is easily
perceived that in the first-mentioned arrangement, where the moving of
the gas is produced by means of a plunger, a very considerable part of the
generator must be occupied thereby, and that consequently the inner
space of the generator must be very much greater than the volume of
the gas contained therein. In the last-mentioned arrangement, on the
contrary, one can let the gas contained in the generator fill, if not its
whole volume, at least the greatest part, whence it follows that the latter
can be made considerably less in this case than in the other.
Besides this, the gas will now during the whole stroke come into
contact with the immediately heated bottom of the generator; while, on
the contrary, in the first-mentioned contrivance the gas will, during a
part of the stroke, be heated through contact with a part of the gene-
rator which has been heated only by means of the conducting of heat
from below, and consequently cannot be quite so warm as the bottoni.
The heating of the gas must consequently be effected with greater
certainty and to a higher degree in the process now described than in
the other. Besides this, that advantage is gained, that the engine can
be heated in a much shorter time, as it is now only necessary to warm
the bottom in order to put the engine in motion, while in the first-
mentioned process this could not be effected before the heat had propa-
gated itself a considerable distance up the walls of the generator, and
for which purpose a rather long time is necessary.
From what has been above stated respecting the gas engine arranged
in either the one or the other mauner, it appears that its power depends
in a very great measure on the difference between the temperatures of
the heated and the cooled gas; but it is also evident that it equally much
depends on the degree of compression which the gas received from the
beginning. The calculation shows that the gross power of the engine
under else similar circumstances is in direct proportion to the primitive
degree of compression in the gas. In order to double or treble the
power of the engine, it is consequently only necessary by means of the
forcing pump to double or treble the quantity of gas contained in the
generator, and there are no other bounds for the power of the engine

page_text: than those which are determined by the strength of its walls and other
parts, and the perfection of the joining.
Hitherto I have only mentioned in general that in the gas engine
a. permanent gas is used, without naming particularly any certain
kind. When only the power of the engine is taken into consideration,
it is of no importance what kind of gas is used; such, however, will
not be the case if the attention be directed to other circumstances.
If, for instance, we should use atmospheric air, which of all permanent
gases is the most accessible, this would through the oxygen contained
in it oxidise, and consequently destroy the heated parts of the engine
with which it canie into contact. If, on the contrary, a gas free from
oxygen be employed, or at least one which en coming in contact with
heated metal does not impart its oxygen, this gas cannot act injuriously
on the engine. When it is also necessary to take into consideration
the facility of obtaining the required quantity of gas, no other kinds
of simple gases can very well here come in question than hydrogen
and nitrogen. Of these bydrogen is perhaps that which can most
easily be obtained; but it has other inconveniences which render it
decidedly inapplicable. Its use. might, for instance, lead to dangerous
explosions in case the machinist from inattention allowed atmospheric
air to enter the engine together with it. Besides this, it would from its
low specfic weight escape, in consequence of the unavoidable want of
perfect tightness in the engine, in a much greater quantity than a heavier
gas. That supplying pump, which in all cases will be necessary in order
to compensate the wasted gas, should from this cause be fourteen times
greater if hydrogen be used than if atmospheric air be employed.
Nitrogen would be in all respects advantageous if a separate operation
were not necessary for its production, which operation, though certainly
nt difficult or particularly expensive; ought nevertheless to be avoided
if possible. The most applicable kind of gas I consider to be that
mixture of nitrogen and carbonic oxide which is obtained when
atmospheric air is led slowly over red hot charcoal. From what has
been stated above respecting the gas engine, it is evident that it can be
employed both as single and double acting. Many cases can also occur
when it is more, advantageous to employ the former than the latter;

page_text: it must however be considerably modified in order not to cause certain
very important inconveniences. We know that the power of a single
acting engine depends on the difference between a greater and a less
pressure occurring in the generator; and besides that, even the least
occurring pressure must exceed that of the atinosphere if one will
derive sufficient advantages from the engine. It is therefore clear that
the piston must always, through the very arrangement of the engine, be
carried in one and the same direction, and its return in the contrary
direction must therefore be produced by the application of an exterior
power corresponding to the average pressure in the generator. Such an
exterior power might be obtained either through the immediate loading
of the piston rod, or through an excentrically applied weight on
the fly wheel; but it is easy to see what great practical inconve-
niences must arise from both these methods. If several single acting
cugines be used at once, they can certainly be so united with ench
other that the one in rising depresses the other; but at all events
those parts of the engine by means of which the connection had
been effected would be tried by a much greater pressure than that
which would be employed usefully, that is to say, with the sum of
those pressures produced by all the engines, while on the contrary the
useful effect will in general depend on their difference. Besides, in
such a single acting engine in which one side of the piston stood in
imeliate contact with the exterior air, a very considerable waste of
gas would always take place through the want of tightness in the pack-
ing of the piston itself, and consequently very considerable supplying
pumps would become necessary. All these inconveniences can, how-
ever, easily be prevented by uniting that end of the cylinder which is
not in communication with the generator with a reservoir, into which
gas is pumped to the average pressure in the generator. If three sin-
gle acting engines work upon the same shaft by means of cranks which
are 120° degrees from each other, it is then, however, for very evident
reasons, not necessary to have any reservoir; one need then only to put
their cylinders in connection, and pump gas therein to the average
pressure in the generators. That the power of the engine, through the
arrangement in question, is neither increased or diminished, it is evident.

page_text: It aims only at a more even distribution of the power in every revolu-
tion it makes. Finally, I consider it necessary to state that the gas
engine can, although retaining its peculiarities, be arranged in very
many different manners. Thus both the generators and the cylinders
can be placed in a horizontal or inclined position, be changed against
cylindrical sectors, or, in general, can take all the different forms which
have hitherto been employed in steam engines. Besides this, I ought
to add, that the advantages sought by leading the gas into the gene-
rator through a number of holes or openings, evenly distributed through-
out the whole of its bottom or lid, can be gained in several different
ways. Thus, for instance, the perforated plate can be changed for one
or more metal wire webs, or for a layer of evenly distributed small
bodies of spherical, cylindrical, or other form, the spaces between which
can in the same manners the holes in the perforated plate served for
gaining the above mentioned object.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Fabian Wrede in the Great Seal Patent Office,
on the 9th January 1854.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I,
FABIAN WREDE, of Stockholm, in the Kingdom of Sweden, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing late the Eleventh day of July, A.D. 1858, in
the seventeenth year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said Fabian Wrede, Her special
licence that I, the said Fabian Wrede, my executors, administrators,
and assigns, or such others as I, the said Fabian Wrede, 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

page_text: GAS AND AIR ENGINES," upon the condition (amongst others) that I, the
said Fabian Wrede, by an instrument in writing under my hand and
seal, 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 Fabian Wrede, 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 thereof (that is to say):
perma-
Under the denomination of "gas engine" I understand an engine
which, for producing mechanical effect, employs the dilation of
nent gases by heat, in accordance with the following not new principle,
videlicet:
One and the same mass of gas is moved backwards and forwards
between two different rooms, in such a manner that it does not undergo
any change in its volume through the transportation. During the
transport from the one room to the other it is alternately heated and
cooled, by which means its elasticity is alternately increased and di-
minished. The mass of gas in question is in constant communication
with the one end of a common working cylinder, on whose piston it
will consequently exercise an alternately stronger and weaker pressure,
and cause it to move backwards and forwards, in the same manner as
in steam engines. The transport of the gas can be effected in two
quite different manners, videlicet, either A,) by moving the gas from the
one part of a closed vessel to another, by means of a plunger, which
fills up a great part of its interior volume, or B,) by expelling the gas
from a cylindrical or prismatical vessel by means of a piston, letting it
pass freely through an exterior communication, either to the other end
of the same vessel (that is to say, on the other side of the piston,) or
into another vessel, whose piston moves in such a manner that the gas
will not undergo any change in its volume through the transporting
process. The improvements which I have made in the gas engines
refer principally to the latter of the above mentioned methods of

page_text: .
moving the gas, or that which is stated under B. In order to explain
these improvements, and show clearly the advantages gained by them,
we mus call to mind a distinguishing property in gases generally, that
of being extremely bad conductors of heat. In consequence of this
property it is evident that if a mass of heated gas could be moved into
a vessel of a lower temperature in such a manner that no motion arose
within the gas itself, then only the exterior parts of the mass, or those
which immediately touched the walls of the vessel, would be cooled by
them; while, on the contrary, the rest of the mass would retain its
higher temperature, till the streams by degrees arising had had time to
develope themselves. If we now imagine, in accordance with what has
been above pointed out, that the gas by means of a piston is forced out
of the upper part of a cylindrical vessel, and that by means of an exterior
pipe of communication it is introduced into the lower part of the same
vessel, it is evident that it must there flow in with a velocity: greater
than that of the piston, in the same proportion as the area of the latter
is greater than the area of the opening of the pipe. It must conse-
quently reach the lower surface of the piston, spread itself along it, and
then descend along the walls of the vessel in consequence of the sucking
arising in the lower corners; and it is consequently evident that if the
gas enter, hented to a higher temperature than that of the walls of the
vessel, it must soon be cooled by them, so that no advantage can be
derived from the greater degree of heat. If, on the other hand, in-
stead of flowing in through a single opening at the bottom of the vessel,
the gas is introduced through a great number of small holes equally
distributed over its whole surface, the case will be quite different.
The greater velocity with which the gas even now flows in through the
small holes is soon neutralised by the sucking arising between them;
and the greater circulating motion, which in the former case would put
almost the whole mass of gas in contact with the walls of the vessel,
will now be exchanged for a motion of the gas which on the whole
will be an even one, and consequently only the outer parts of the same
come in contact with the vessel. Those advantages which are gained
by this arrangement can be obtained in several different manners, of
which I consider the following the most simple and applicable: A, B, C, D,

page_text: (Figure 1,) represents a closed cylindrical generator (by which ex-
pression understand the vessel in which the alternate heating and
cooling of the gas is produced,) and E, F, G, H, another cylinder,
enclosed in the same, the exterior diameter of which is so much less
than the inner one of the former that the space between them forins
a sufficiently spacious channel of communication between the upper
and the lower parts of the gencrator. The inner cylinder is closed
with a lid at the upper end, and one at the bottom, supplied with a
great number of small holes. Between those lids and those of the
outer cylinder is a space of about the same thickness as between the
walls of the two cylinders. When now the piston K, is raised the gas
above it is forced to rise through the holes in the upper lid E, F, in
order afterwards to descend through the space between the cylinders,
and to enter between the bottoms C, D, and G, H, and flow into the
lower part of the generator through the holes in the inner bottom G, H.
It comes consequently into immediate contact with the two 'bottoms,
which are warmed by the furnace, and it must therefore on entering the
generator be of nearly the same temperature as they are, very little of
which will, according to what has been shown, be lost during the motion
in the generator. When the piston is again lowered the gas goes. in
an inverted order, and must then enter above the piston, cooled by the
water introduced above the lid A, B. As well through the alternate
influence of the warm and cold gas on the walls of the cylinders; as
through their peculiar conducting power, the walls will by degrees as-'
sume a state of temperature decreasing from below upwards, by which
means the heating and the cooling of the gas will be almost entirely
eflected in the space between them. That the generator must be sup-
plied with a side opening, through which it stands in constant commu-
nication with one end of a working cylinder, in the same manner as has
before been pointed out, and that the transporting piston must be moved
by the engine in about the same manner as the valves of a steam engine,
is of course taken for granted. When the heated gas rises from the
warm to the cold end of the generator through the space between the
two cylinders intended for this purpose, it imparts a considerable porțion
of its heat to their walls, and comes in between the two lids considerably

page_text: cooled, on which account only a small part of its original heat need be
taken away by means of the cooling water. The more completely this
can be produced, the more advantageous it is, because the heat im-
parted in the first mentioned manner is not lost, but will in a very con-
siderable degree be again taken up when the cooled gas is again led
back in the contrary direction. In order to obtain this object it is
necessary that the space between the cylinders must be made as narrow
as possible. As, however, this space must form a sufficiently spacious
communication between the two ends of the generator, it cannot be
diminished beyond a certain degree. The greater the generator is, the
wider must this space evidently be; and in greater engines it should be
so large that the stream of gas flowing through it can but imperfectly
impart its heat to the surrounding walls, or receive it again from them.
In order to avoid this difficulty, one can place between the two before
mentioned cylinders one or more intermediate, by which means the
stream of gas can be divided into two or more, each of which can then
receive the necessary thinness. Figure 2, shows a generator arranged
in this manner. The intermediate cylinder is in the Figure divided
lengthwise into two, in order to form round the generator a sufficiently
spacious communication with the working cylinder. If the two halves
thus arising be again divided into two or more parts, that advantage
is gained, that the conducting of heat from below upwards will be con-
siderably diminished. Experience has shown me that the manner in
which the perforated plate is fixed to the bottom or lid of the generator
is by no means indifferent. If it is placed so that it either not at all,
or only at few points, touches the lid of the generator, it will have a
very different temperature from that of the latter, whence it is clear
that a considerable loss of power must arise. In order to prevent this,
one ought to give the plate and the lid as many points of connection, or,
more correctly speaking, as great surfaces of contact as possible, without
hindering or obstructing the free passage of the gas between them.
Figure 3, shows how I have endeavoured to produce this in those
models I have hitherto had made. A, B, represents the perforated
plate, and c, d, c, d, elevated parts thereon, the height of which parts
above the surface of the plate is equal to the space which is to be

page_text: between the plate and the lid of the generator, and whose upper surfaces
come into perfect contact with the last mentioned. In order still fur-
ther to promote the communication of heat between the lid or bottom
of the generator and the perforated plates, the latter ought to be made
of copper or some other good conductor of licat.
The advantages arising from the manner of moving the gas now
described, compared with the first mentioned, are now evident. It is
casily perceived that, in the first mentioned arrangement, where the
moving of the gas is produced by means of a plunger, a very con-
siderable part of the generator must be occupied thereby, and that
consequently the inner space of the generator must be very much
greater than the volume of the gas contained therein. In the last
mentioned arrangement, on the contrary, one can let the gas contained
in the generator fill, if not its whole volume, at least the greatest part,
whence it follows that the latter can be made considerably less in this
case than in the other. Besides this, the gas will now, during the whole
stroke, come into contact with the immediately heated bottom of the
generator; while, on the contrary, in the first mentioned contrivance, the
gas will, during a part of the stroke, be heated through contact with a
part of the generator which has been heated only by means of the con-
ducting of heat from below, and consequently cannot be quite so warm
as the bottom. The heating of the gas must consequently be effected
with greater certainty and to a higher degree in the process now de-
scribed than in the other. Besides this, that advantage is gained that
the engine can be heated in a much shorter time, as it is now only
necessary to warm the bottom in order to put the engine in motion,
while in the first mentioned process this could not be effected before
the heat had propagated itself a considerable distance up the walls of
the generator, and for which purpose a rather long time is necessary.
From what has been above stated respecting the gas engine, arranged
in either the one or the other manner, it appears that its power depends,
in a very great measure, on the difference between the temperature of
the gas in the warm room and in the cold room; but it is also evident
that it equally much depends on the degree of compression which the
gas received from the beginning. The calculation shows that the gross

page_text: power of the engine, under clse similar circumstances, is in direct pro-
portion to the primitive degree of compression in the gas. In order to
double or treble the power of the engine it is consequently only neces
sary, by means of the forcing pump, to double or treble the quantity of
gas contained in the generator; and there are no other bounds for
the power of the engine than those which are determined by the
strength of its walls and other parts, and the perfection of the joining.
Hitherto I have only mentioned in general, that in the gas engine a
permanent gas is used, without naming particularly any certain kind.
When only the power of the engine is taken into consideration, it is of
no importance what kind of gas is used. Such, however, will not be
the case if the attention be directed to other circumstances. If, for
instance, we should use atmospheric air, which of all permanent gases is
the most accessible, this would, through the oxygen contained in it, at
length oxidise, and consequently destroy the heated parts of the engine
with which it came into contact. If, on the contrary, a gas free from
oxygen be employed, or at least one which, on coming in contact with
heated metal, does not impart its oxygen, this gas cannot act injuriously
on the engine. Nitrogen would be in all respects advantageous, if a
separate operation were not necessary for its production, which opera-
tion, though certainly not difficult or particularly expensive, ougth
nevertheless to be avoided if possible. Hydrogen can more easily be
obtained, but it has other inconveniences which render it decidedly
inapplicable. Its use might, for instance, lead to dangerous explosions,
in case the machinist, from inattention, allowed atmospheric air to enter
the engine together with it. Besides this it would, from its low specific
weigth, escape, in consequence of the unavoidable want of perfect
tightness in the engine, in a much greater quantity than a heavier gas.
That supplying pump, which in all cases will be necessary in order to
compensate the wasted gas, should from this cause be about fourteen
times greater if hydrogen be used than if atmospheric air be em-
ployed. The most applicable kind of gas I consider to be that mixture
of nitrogen and carbonic oxide which is obtained when atmospheric air
is led slowly over red hot charcoal. If the engine be heated with
charcoal or cokes, the easiest manner of obtaining the above mentioned

page_text: mixture will be to take it from the fire place of the engine through a
pipe for this purpose introduced therein. From what has been above
stated respecting the gas engine, it is evident that it can be employed
both as single and as double acting. Many cases can also occur when
it is more advantageous to employ the former than the latter. It must
however then be considerably modified, in order not to cause certain
very important. inconveniences. We know that the power of a single
acting engine lepends on the difference between a greater and a less
pressure occurring in the generator; and besides, that even the least
occuring pressure must exceed that of the atmosphere, if one will
derive sufficient advantages from the engine. It is therefore clear that
the piston must always, through the very arrangement of the engine, be
carried in one and the same direction; and its return in the contrary
direction must therefore be produced by the application of an exterior
power, corresponding to the average pressure in the generator. Such
an exterior power might be obtained, either through the immediate
loading of the piston rod, or through an excentricaly applied weight on
the fly wheel; but it is easy to see what great practical inconveniences
must arise from both these methods. If several single acting engines
be used at once, they can certainly be so united with each other that
the one in rising depresses the other; but at all events those parts of
the engine by which the connection had been effected would be tried
by a much greater pressure than that which would be employed use-
fully, that is to say, with the sum of those pressures produced by all the
engines, while, on the contrary, the useful effect will in general depend
on their difference. Besides, in such a single acting engine, in which
one side of the piston stood in immediate contact with the exterior air,
a very considerable waste of gas would always take place through the
want of tightness in the packing of the piston itself, and consequently
very considerable supplying pumps would become necessary. All these
inconveniences can, however, easily be prevented by uniting that end
of the cylinder which is not in communication with the generator, with
a reservoir into which gas is pumped to the average pressure in the
generator. If three single acting engines work upon the same shaft, by
means of cranks which are 120 degrees from each other, it is then,

page_text: however, for very evident reasons, not necessary to have any reservoir;
one need then only to put their cylinders in connection, and pump gas
into them to the average pressure in the generator. That the power of
the engine, through the manner of proceeding in question, is neither
increased nor diminished, is evident; it aims only at a more even
distribution of the power of the engine in every revolution it makes.
Finally, I consider it necessary to state that the gas engine can,
although retaining its peculiarities, be arranged in very many different
manners. Thus both the generators and the cylinders can be placed in
a horizontal or inclined position, be changed against cylindrical sectors,
or in general can take all the different forms which have hitherto been
employed in steam engines. Besides this, I ought to add that the
advantages sought by leading the gas into the generator through a
number of holes or openings evenly distributed throughout the whole of
its bottom or lid, can be gained in several different ways. Thus, for
instance, the perforated plate can be changed for one or more metal
wire webs, or for a layer of evenly distributed small bodies of spherical,
prismatical, or cylindrical form, the spaces between which can, in the
same manner as the holes in the perforated plate, serve for gaining
the above mentioned object.
In witness whereof, I, the said Fabian Wrede, have heretofore set
my hand and seal, Stockholm, this Third day of December,
ADD 1959
FAB. WREDE. (1.s.)