AN IMPROVED MODE OF GENERATING STEAM FOR MOTIVE POWER, AND IN VALVES OF ENGINES FOR RECEIVING SUCH STEAM
Year: 1873

page_text: LETTERS PATENT to Frederick Curtis, of Boston, in the County of
Suffolk, and State of Massachusetts, United States of America, for
the Invention of "AN IMPROVED MODE OF GENERATING STEAM FOR
MOTIVE POWER, AND IN VALVES OF ENGINES FOR RECEIVING SUCH STEAM."-
A communication by John Henry Mills, residing at Boston, in the
County of Suffolk and Stato of Massachusetts, United States of
America.
—
5
COMPLETE SPECIFICATION filed by the said Frederick Curtis at the
Office of the Commissioners of Patents, with his Petition and
Declaration, on the 28th May 1873, pursuant to the 9th Section of
the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, FREDERICK
CURTIS, of Boston, in the County of Suffolk, and State of Massa-
chusetts, United States of America, send greeting.

page_text: RECEIVING SUCH STEAM," and have petitioned Her most Excellent Majesty
Queen Victoria to grant unto me, my executors, administrators, and
assigns, Her Royal Letters Patent for the same, and have made solemn
Declaration that the same has been communicated to me by John
Henry Mills, resident at Boston, in the County of Suffolk, and State of
Massachusetts, United States of America.
NOW KNOW YE, that I, the said Frederick Curtis, do hereby declare
the nature of the said Invention to be as follows:-
The first portion of this Invention has for its object the generation
of steam directly from a substance more volatile than water, in order
that a given power may be obtained from a less quantity of fuel than
by methods heretofore practiced, and to the end also that the use of
water may be economized and space utilized on board marine vessels,
and in other localities; a further object of the Invention being to
secure absolute safety against danger of explosion, or encrustation of
the generator.
This Invention, in principle, consists briefly in the employment of
hot water or other proper or equivalent liquid, substance, or medium,
and a fluid more volatile than such water or medium, in order that the
heat of the former may generate steam from the latter. Various
experiments have been conducted for the last twenty-five years in the
cffort to generate steam from a more volatile fluid than water, but have
generally failed, for the reason that the comparatively sensitive and
explosive nature of the fluid would not admit of a controllable direct
application of heat for the purpose of vaporizing it.
Recently a compound engine has been devised, in which an ordinary
steam generator and engine is employed, and the exhaust steam from
the primary cylinder is used to heat and vaporize a more volatile fluid
placed within a second generator, the steam thus generated passing
into a second cylinder and opering its piston. This method requires
two generators and two engines in addition to a condensing apparatus,
as the high cast of the volatile fluid renders it necessary to employ a
condensing apparatus to avoid waste of material. If the first cylinder
of this engine gives one hundred horse power, and the second one
hundred and fifty, which is not an extravagant ratio as appears from
actual experiments, it is evident that two fifths of the power of the
entire machine must be obtained by the ordinary consumption of coal.

page_text: In this engine a volatile fluid is vaporized directly by the heat of hot
water, or oil, or other medium, and is admitted directly to the cylinder
of a steam engine, and as this medium when water is used is never to
exceed a temperature of 212° the boiling point (which gives about
sixty-five pounds of steam), it will be seen that it economizes the
entire amount of fuel used to a corresponding degree, and that the
expense and friction of the steam generator and primary cylinder, which
is requisite in the Invention above named, using a steam engine is
avoided.
Of the various volatile fluids which are available for the purpose is
preferably employed bi-sulphide of carbon, as imparting good results.
at comparatively low cost, this liquid rendering steam of a pressure of
about sixty-five pounds to the square inch from 212° heat.
The mechanical equivalent of heat contained in one pound of steam
from water at 32° Fahrenheit is 885,175.2 foot pounds, of which 966°•6
or 746,215.2 foot pounds, 85 per cent. of the whole (assuming the
expansion to be the pressure of the atmosphere) is thrown away by
those engines that exhaust directly into the atmosphere; and 541° or
417,652 foot pounds, 47 per cent. of the whole, in condensing engines
(assuming the vacuum to be perfect and feed water to be heated to the
boiling point) is wasted.
By the use of sulphuret of carbon or other fluid more volatile than
water it ought not to be claimed to store up in the generator more
power for each unit of heat than by the use of water, but the cohesivo
power of the atoms of water being so much more than many known
liquids, the "latent heat" or power though stored up in the steam
generator from water (being at least 85 and 47 per cent. respectively,
in the two cases above mentioned,) is unavailable as power. Experiments
have demonstrated that engines can be run with the steam from the
more volatile liquids with as little loss from friction and any other ways
as with steam water, thus saving the above described loss almost
entirely, since the "latent heat" is comparatively insignificant.
It will thus be seen that any device which will enable steam to be
employed from the more volatile fluids directly will be of incalculable
benefit, and doubly so in this Invention, since it accomplishes the
desired result at a much less first cost than in ordinary generators, and
especially in the use of two engines and two generators.

page_text: The Drawings accompanying this explanation represent in Figure 1 a
vertical section, and in Figure 2 a horizontal section of one form of a
steam generator and motor and their adjuncts, in which the principles
of this Invention may be carried out, and in this instance a double
cylinder engine is adopted, that is to say, one containing two cylinders;
a primary one in which direct steam is employed, and a second of
larger diameter in which the expansive steam from the first operates;
this duality of cylinders however being in nowise essential to the
developement of the principle of this Invention, but being embodied
herein as exhibiting to perhaps better advantage the merits of such
principle.
Figures 3, 4, 5, and 6 of the accompanying Drawings represent
vertical sections, and Figures 7 and 8 transverse and horizontal sections
on a reduced scale of the two cylinders, steam chests, valves, and
cranks, and their adjuncts, which are employed in carrying out the
second portion of this Invention.
In the above named Drawings accompanying this Specification and
illustrating this Invention in one practical form of embodiment, As
represents an upright cylindrical shell or structure which encloses within
it the greater portion of the entire steam generating apparatus. Within
the upper part of this shell A³ is disposed a water receiving and heating
tank B, of somewhat less diameter, in order to obtain a heat and smoke
distributing chamber C³ from the upper part of which a smoke discharge
flue D³ conducts the smoke, gases, and waste products of combustion
from the furnace below.
The water reservoir may be closed at the top, and provided with a
safety valve weighted to the desired extent provided any steam is to be
generated from the water within it, but for most purposes it is intended
that the water shall not exceed a temperature of 212° Fahrenheit,
therefore the filling orifice of the heating tank may be open to the
atmosphere in order to prevent the water or liquid from acquiring a
greater temperature, thus entirely obviating danger of accidental
explosion; or, what would be preferable, a very light weight which one
pound of steam would raise might be placed upon the safety valve to
prevent the slow atmospheric evaporation of the water which might
otherwise ensuc. Within the water heater C³ is disposed the generator
E3 which may be of any suitable form, as it is not limited in this respect;

page_text: the generator as herein shown consisting of a series of upper and lower
horizontal pipes a³, a³, a³, a*, a³, etc., connected by vertical ranges b³, b³,
, etc., open communication being established between them, and the
entire cluster submerged partially or entirely in the water contained in
3 the tank B³.
The steam delivery pipe leading to the cylinder of the engine is shown
at 1³, as erected upon and communicating with the interior of one of the
upper pipes a³, thence rising through the dome of the structure A³ and
passing to the engine cylinder, which is represented in this instance at
A as a vertical one, and situated at one side of the structure A³. The
driving shaft of the engine which is horizontal hercin is shown in the
Drawings at F as revolving in bearings I, I, crected upon the dome of
the shell A³; the piston rod of the cylinder A being shown at D, the
connecting rod of the same at D³, and its crank at E, the valve rod at
Hand its pitman at H³ and eccentric at I, such parts being arranged
after the ordinary method of vertical steam engines.
The furnace of the apparatus is shown at M³ as of any proper con-
struction, and disposed below the water heating tank B³, and within and
spanning the area of the structure A³, the ash pit shown at N³ being
disposed below the furnace in the usual manner.
As the engine hercin illustrated is a condensing engine, to prevent
waste of the material within the generator (which material preferable
at present should be bi-sulphide of carbon) a suitable condenser must be
provided, and to this end is disposed in a close chamber or drum 03
which is situated below the ash-pit a cluster or coil of pipe P³; the
chamber being to receive the exhaust steam from the engine cylinder,
and the pipe to receive a current or blast of cold air from a blowing
engine to immediately condense the steam surrounding it.
The exhaust pipe is shown in the Drawings at Q³, as leading from the
cylinder A and passing horizontally through the lower part of the water
tank B³, thence into and discharging within the condenser, as shown in
Figure 1 of the Drawings.
The feed water which returns from the condensing tank O³ to the
generator, is clevated from such tank by a suitable force pump which is
exhibited in the accompanying Drawings at S³, its suction pipe for
taking the condense water being shown at f³ and its discharge pipe,

page_text: which ejects it into the generator being shown at g³, the latter leading
from the pump to and discharging into one of the lower pipes a* of the
generator.
The valve rod of the pump S³ is shown at ct, its pitman at d', and its
eccentric at e', the latter being mounted upon the driving shaft F before
alluded to.
The operation of this engine being on the principle of any condensing
engine will be readily understood. The vapor or steam from the volatile
and sensitive fluid within the generator B³ passes through pipe F³ into
the cylinder A, and having performed its office therein exhausts through
pipe Q³, or the passage between the two cylinders, into the condenser O³,
from whence it is raised by the pump S³, and injected into the generator
B³ to be reconverted into steam by the heat of the water surrounding
such generator.
As herein-before stated, the principle of this Invention appears to good
advantage when applied to the double cylinder engine; therefore a
second cylinder in the present instance is adopted which is shown in the
accompanying Drawings at C¹ as a vertical one, and disposed alongside
of the structure A³ in a manner similar to the disposition of the primary
cylinder G³, but upon the opposite side of such structure. The exhaust
steam in pipe Q³ after passing through the heating medium in tank C
enters the cylinder A', and actuates its piston and exhaust from thence
into the condenser O or into the atmosphere, as the case may be.
The second portion of these improvements consist in a certain con-
struction and arrangement of valves and cranks of double cylinder
engines as herein explained. In reciprocating steam engines which take
steam at the beginning of the stroke of the piston and cut it off at five-
eighths its stroke or thereabouts, the steam acts to much advantage upon
the crank only during about three-fourths the revolution of the latter,
owing to its passing the dead center twice during such revolution, con-
sequently in single cylinder engines much of the power of the steam is
wasted. To overcome this difficulty in part, but more especially to
obtain an increased power by utilizing the exhaust steam of a cylinder,
a second cylinder has been beretofore employed of larger diameter than
the first, into which such exhaust steam has been admitted, the supposed
gain being that due to the increased diameter of the auxiliary cylinder
and piston over that of the primary piston, less the friction resulting

page_text: from the additional cylinder and its adjuncts, the rapid reduction in
the pressure of the steam, the increased friction, and the back pressure
upon the first piston, however, reduced the gain to a very small amount
hardly worth the extra cost of the additional cylinder. It might be
urged that an equally good result would follow by omitting the auxiliary
cylinder, and lengthening the primary cylinder and allowing the steam
to expand in the latter until its pressure was reduced to the lowest
effectivo point; but the great length of the crank and its dead center, as
well as other mechanical difficulties, have set a limit to the length of a
cylinder wherein which the full power of the steam can be obtained.
In double cylinder engines as heretofore made, the two cranks at the
point of receiving and discharging steam of the first cylinder are
necessarily opposite cach other, and consequently on their dead centers
at the same time, for the reason that the exhaust steam from the first or
primary cylinder does not take place until its piston reaches the end of
its stroke, while such piston during its entire return travel is met by and
obliged to contend against the back pressure resulting from the action of
the exhaust steam upon the larger piston during said entire return
stroke. The purpose of this second portion of these present improve-
ments are to obtain such a construction and adaptation of the valves of
double cylinder engines that the exhaust from either end of the first
cylinder shall take place simultaneously with "cut off" of direct steam
from it, without regard to the point at which such "cut off" may be
effected, the valve of the first cylinder having the necessary lap to effect
the "cut off," while the secondary cylinder valve has no "lap," the
arrangement of the whole being such that exhaust and expanding steam
from the primary cylinder is admitted to the second cylinder alternately
on each side of the piston of the latter during the entire stroke of such
auxiliary piston, the exhaust from the said auxiliary cylinder being open
upon the opposite side of its piston, also during the entire stroke of the
latter, for which reasons the cranks can be set at any position relative to
one another that may be desired, and allow the crank of one piston to be
assisted over its "dead point" by the full power of the other acting to
its greatest advantage.
This construction and adaptation of valves will be enabled after
"cutting off" steam in the primary cylinder to neutralize the effect of
the expanding steam upon the first piston, and avoid back pressure there-
upon, and allow said expanding steam to exhaust or pass from the

page_text: primary cylinder to and act full upon the auxiliary cylinder (and as
before stated act upon the latter during its entire stroke), and to obtain
the advantages of such results during both strokes of both pistons, as
steam is taken from the steam chest at both ends of the primary piston,
and balance this piston during the remainder of its stroke after "cutting
off." By this construction of valves in relation to the cylinder ports by
which the exhaust or escape from the first cylinder is opened, at
the moment of " cutting off" the direct steam therein the cranks
of the two cylinders are enabled to be set at or about at right
angles to each other, and advanced nearly half its stroke before
the first piston has completed its stroke and is
the expanding steam being exerted to the best
both pistons at the same time has so reduced the back pressure of
such steam upon the primary piston (which takes place during a part of
the return stroke of such piston) that this back pressure amounts to but
a fraction of what would ensue should the steam in the primary cylinder
not begin to exhaust until its piston is obliged to encounter a heavy
back pressure during its entire return stroke as is the case in double
cylinder engines heretofore devised.
about to return,
advantage upon
In carrying out the second portion of this Invention, two steam chests
and two valves are employed, one to each cylinder; cach valve rod and
eccentric being connected with the main or crank shaft.
In the Drawings, A, A¹, represent two cylinders which may be of
equal or unequal diameter, but preferably of like length, disposed along-
side of cach other and parallel to one another, and substantially in the
same plane. The steam chest of the first or primary cylinder A. is
shown at B, and that of the auxiliary or expansion cylinder A' at B',
the piston of the cylinder A' and C¹. The rod of the piston C is shown
at D, and of the piston Cat D¹, each being connected to a crank E
or E' formed upon the main or crank shaft F of the engine. The valvo
of the cylinder A is shown at G, and the rod of such valve at H, while
the valve of the cylinder A¹ is shown at G¹, and its rod at H'. The
eccentric or crank wheel of the valvo G is shown at I, and of the
valve G¹at I¹, each eccentric or wheel being secured to the crank
shaft F. As herein shown the two cranks E, E, are placed at right
angles or "quartering" as it is termed with each other, although this
relative position is not arbitrary, but may be changed at pleasure. The
steam ports of the primary steam chest B, and the primary cylinder A

page_text: are three in number, that is to say, two direct end ports a, a¹, and an
intermediate exhaust port which discharges into the steam chest B₁ of
the auxiliary cylinder, while the ports of the auxiliary cylinder A' are of
like number and disposition, and are shown at c, c', and d, the latter
being the exhaust and discharging into the atmosphere. Each valve is
of like shape, and is formed with a central cell or enclosure c or e' which
constitutes at alternate intervals of time, a continuation of one end port
of its respective cylinder to open communication between such port and
the exhaust port of said cylinder. The valve G has in the present
instance a "lap" which cuts off direct steam at about five eighths the
stroke of the piston C, while the valve G' has no "lap" in order that
the steam may enter and exhaust to and from the cylinder A during the
entire stroke of its piston.
In describing the operation of this portion of this Invention, assuming
as a starting point that the various parts are in the positions shown in
Figure 3 of the Drawings, that is, with the primary piston C at its
extreme position to the left end of its cylinder A, and the auxiliary
piston C at the center of the cylinder A', the crank E being horizontal,
and the crank E' vertical, but below the center of the crant shaft. The
crank shaft is to rotate in the direction of its arrow, that is to the right,
consequently the piston C will begin to travel in the direction of its
arrow in said Figure 3, and the piston C¹ in the opposite direction. The
valve G by the action of its eccentric I moves in the direction of its
arrow in Figure 3, and begins to open the port a and allow direct steam
from the steam chest B to enter the primary cylinder A, and behind its
piston C thus advancing the latter in the direction of its arrow in said
Figuro 3 of the Drawings. The valve G and piston C travel in the
same direction until the latter has traversed about one half its "stroke,"
when the valve reverses its movement, and by the quick action of its
cccentric returns with such rapidity that by the time the piston has
effected five-cighths its "stroke" or thereabouts, the valve has passed
over and closed the mouth of the port a, and "cut off" steam from the
steam chest, as shown in Figure 5 of the Drawings, the valve continuing
to travel in the last named direction, and the piston in its original
direction until the latter reaches the opposite end of the cylinder and
completes its "first stroke," the valve at such time entirely closing the
mouth of the port a¹, as shown in Figure 4 of the Drawings. In the
accompanying Drawings the two eccentrics or the wrist pins of the

page_text: crank wheels I and I' are set at about right angles to one another, and
are of such respective length that the piston C and C¹ stand at opposite
or about opposite ends of the cylinders.
As the piston C is being driven through its first stroke as last
explained, the cell e of the valve G has iniated and maintained free and
open communication between the port a¹ and the exhaust port b, and as
this exhaust port leads to and freely communicates with the interior of
the steam chest B₁ it follows that the exhaust steam from the primary
cylinder escapes before the advancing piston C through the said port
a¹ and into the auxiliary steam chest B. The port c¹ of the auxiliary
cylinder A' is at this time (that is, while the piston C is traveling half its
first stroke) open, such opening having been effected by the travel of
the valve G'in the direction of its arrow in Figure 3, and allowing steam
from the steam chest B to enter such cylinder by means of ports a¹ and
b, and cell e as before stated, and drive the piston C¹ in the direction of
its arrow in Figure 3 of the Drawings to the midway or about midway
point, shown in such Figure, said steam having been during the
preceding stroke of the primary piston admitted to the auxiliary steam.
chest B' through the coinciding or connecting of the port a, cell e, and
exhaust port b.
The piston C¹ continues to travel in the direction last named until it
reaches the end of its cylinder, at which point the valve G¹ has closed
port c¹ to the entrance of steam from the chest B' and begins immediately
with the return start of the piston to reverse its movement and open
communication between cylinder A' and final exhaust passage d of a
cylinder C¹ by means of cell e¹, thus permitting the cylinder A¹ to
exhaust into the atmosphere during the entire stroke of its piston as the
cell e¹ is sufficiently long to allow this to be done, and as the eccentric
I is actuating the valve very slowly while the piston C is advancing
very rapidly. As the piston C¹ completes its stroke as last stated, the
primary piston has reached its "cutting off" point at about five-eighths
of its stroke as shown in Figure 5 of the Drawings, at which time the
valve G begins to open port c and allow steam which has exhausted
from cylinder A (through ports a and b and cell e into steam chest B')
to enter cylinder A¹ and behind its piston C¹ to drive the latter in the 3
reverse direction last named (or as shown by the arrow in said Figure 5
of the Drawings), such piston C¹ traveling in the same direction for a
time as the primary piston C, or until the latter has completed its first

page_text: traverse as before stated, and arrived at the opposite end of the primary
cylinder, at which time the piston C¹ has effected about half its return
stroke, as shown in Figure 4, in the direction of its arrow in such Figure,
it being observed that immediately after the valve G has closed port a
and shut out direct steam from cylinder A it opens free communication
between the said cylinder A and exhaust port by means of said port a,
and also establishes equality of pressure upon both sides of piston C
owing to port a¹ being open and communicating with cell e, thus
permitting full power of the direct expanding steam of the first cylinder
to enter cylinder A¹ through said port and the port c and steam
chest B', and act upon the piston of such second or auxiliary cylinder
which it does during the entire stroke of the latter. Figure 6 of the
Drawings illustrates this condition of parts.
Having followed the engine through one stroke of cach piston, and as
the action of all the parts is precisely the same throughout the return
stroke, further explanation is deemed unnecessary as it will be at once
seen that as the primary piston begins its return stroke by the opening
of port a¹ by means of the valve G traveling in the direction of its arrow
in Figure 4, the cell e of valve G has opened communication through
ports a and b with auxiliary steam chest B₁ and allows exhaust steam
from cylinder A to enter such steam chest, while simultaneously with
the admission of this steam to chest B¹ the piston C¹ is driven in the
direction last stated or as shown by arrow in Figures 4 and 5 by
steam from port c until it completes its traverse in this direction, at
which time the valve G has reversed its movement and returned
sufficiently for to close port c and open port c¹ and allow the steam
passing from cylinder A as stated to enter cylinder A¹ through port c¹
and effect the return movement of the piston C¹, the two pistons traveling
in the same direction until the primary piston completes its stroke and
reaches the end of its cylinder, and the piston C₁ its midway position,
which brings us to our starting point. It being seen that as the piston
C₁ is making its traverse of the cylinder A¹ in the direction last named,
the port c¹ is by means of the cell c¹ of the valve G¹ in open com-
munication with the exhaust passage d, and the said cylinder A¹ is
exhausting by this means into the atmosphere to which the passage d
leads, it being further observed that as the primary piston in its return
passes its five-eighths stroke or "cutting off" point, the expanding
steam from the primary cylinder passes through ports a¹ and b and

page_text: cell e into cylinder A' through port c¹ of such cylinder and drives piston
C' in the same direction for a time as the primary piston C at the same
time the cell e of the valve G opcus communication between the two
ends of the cylinder A by means of port a and establishes equality of
pressure upon the primary piston C and avoids the back pressure there-
upon which would otherwise cnsuc. There is, provided the cranks are
set at right angles to each other, a short interval of time in which the
steam within the auxiliary cylinder is working expansively upon the
auxiliary piston, that is to say, while the crank of the primary piston is
passing its dead center, and this expansive power of steam is the means
whereby the primary crank is assisted over its dead center, the primary
piston during its stroke performing a like good office for the auxiliary
piston to carry its crank past the dead center.
Among many advantages attaching to this Invention, the following
are prominent :—
First. As tho vapor of the volatile material at 65 pounds, from which
to generate steam contains only about one fourth as many units of heat
or mechanical equivalent as steam from water at the same pressure, and
as a large portion of this heat is utilized in the cylinder of the engine,
the small remaining portion is only to be abstracted to secure the desired
vacuum; and especially if the double cylinder engine before named be
employed, the power obtained from the auxiliary and larger cylinder and
piston would equal if not exceed that derived from the direct pressure
on the primary and smaller piston, for the reason that the small amount
of heat and air to remove from the condenser, enables a vacuum more
nearly perfect to be obtained than could otherwise be effected.
Second. In the event of adopting the double cylinder engine, it is
proposed as herein stated to place the two cylinders and their mechanism
upon opposite sides of the generator, and conducting the exhaust pipe
from the first cylinder through the water or other agent which heats the
steam generating liquid, by which means the construction is simplified
and the cost of the engine reduced, and liability to over pressure of
steam between the cylinders is entirely obviated owing to the uniformity
of temperature of the heating fluid or agent, which never exceeds the
boiling point for the reason that it may be open to the atmosphere if
desirable.
23
Third. An important advantage of this system of generating steam

page_text: the fact that neither the inside or outside surface of the generator tubes
ever become foul or deteriorated, for the reason that the salts and lime
precipitated from water are not present in the volatile fluid to injure
the interior of the tube, and soot cannot get access to the exterior of the
same, for the reason that they are submerged or surrounded by water,
and not exposed at all to the direct action of fire, smoke, or gases.
One of the most vexatious questions and conditions now incident to the
generation of steam is thus done away with.
Fourth. Owing to the low degree of heat required and the immunity
of the generator pipes or flucs from the action of the same, not only
these pipes but the entire furnace is exempt from the rapid destruction
now common to such apparatus, from the excessive heat of the fires.
Fifth. From what has been said it will be evident that in this system
perfect safety from explosion is obtained, since the water or other
heating medium if open to the atmosphere can never derive a
temperature above the boiling point from any degree of heat in the
fire, while as a still further economy and advantage, the loss of heat by
radiation is reduced to a great extent as the temperature of the entire
apparatus is now materially less than when vaporizing water; while if
the fluid in the vaporizing generator should by accident or neglect, be
allowed to entirely evaporate, no injury would result, as the temperature
of the heating medium would not be sufficient to injure such generator.
This engine, as compared with steam, possesses many minor
advantages, and in marine service will be found valuable for the reason
that as a very small amount of fresh water is requisite, no large tanks
or condensing apparatus are necessary, and their space may be used for
freight, also the space now occupied by fuel and by steam boilers and
engines, may be considerably reduced and utilized.
For locomotive engine use the watering stations and the delays
thereat may be avoided, and the stoppages for fuel less frequent.
Owing to the rotative condensing and circulating principle of the
vaporizing fluid involved in this engine, little waste of such fluid results
as the small amount of vapor which would result by reason of bad
joints, etc., in a well made apparatus would be so small a per centage as
not to be of practical account.

page_text: Another great advantage of this present Invention over analogous
ones, is, that it is not restricted to any size of second cylinders relative
to the first, for the reason that both are being driven at the same time,
whereas, heretofore, the forward pressure of the expanding steam upon
the small piston has been counteracted by the back pressure exerted
upon it by the power of the exhaust steam upon the second piston,
consequently, as before premised, the only gain found in this instance
is that due to the increased size of the second piston over that of the
first after deducting the extra amount of labor and friction which the
addition of the second cylinder and its adjuncts entails.
Although having, to avoid prolixity in the accompanying description
of this Invention, alluded to the use of water as a medium of heating
the steam generating fluid, this Invention is not restricted in any sense
to such use, as it may be desirable in many cases to raise the pressure
of steam to a higher point than 212° of Fahrenheit will produce, there-
fore it will be necessary to employ a steam-generating liquid of greater
volatility than bi-sulphide of carbon, or to use a less volatile liquid than
water as a heat-transmitting medium, or one that will require a greater
degree of heat than 212° Fahrenheit to vaporize.
By the use of oils or other substances less volatile than water, a 2
greater degree of heat to the generator may be imparted, and con-
sequently raise the pressure of steam within it, without raising such
substances above 212° of heat, thus, while obtaining as high a pressure
of steam as may be desired never departing from the main beneficial
results of this Invention.

page_text: Third. In a system of generating steam as herein described, in which
two differential cylinders are employed for purposes stated; the method
substantially as herein shown of reheating the exhaust steam in transit
from the primary to the auxiliary cylinder by passing the exhaust pipe
through the heat-transmitting fluid or agent, substantially in manner as
herein-before explained.
Fourth. The general combination of the water receptacle or jacket,
the generator, the condensing apparatus, and the differential cylinders.
Fifth. In double cylinder engines the construction and arrangement
of valves and cranks, whereby the exhaust from the first cylinder takes
place simultaneously or thereabouts with the "cut off" of direct steam
from said cylinder, substantially as and for purposes stated.
Sixth. The construction and arrangement of the valves and cranks of
double cylinder engines, whereby being enabled to so govern the exhaust
from the two cylinders that such exhaust shall both act upon the piston
of the auxiliary cylinder, and escape or exhaust from such cylinder
during the entire stroke of its piston, essentially as and for purposes
stated
In witness whereof, I, the said Frederick Curtis, have hereunto
set my hand and seal, this Seventh day of May 1873.
FREDERICK CURTIS. (L.S.)