TUBULAR BOILER, SUPERHEATING STEAM, AND SURFACE CONDENSER.
"MR. GILBERT, "HAYLE FOUNDRY, _December 14th, 1828_.
"Sir,--On my return from London five weeks since I was disappointed
at not finding you in Cornwall. I have made inquiry into the duty
performed by the best engines, and the circumstances they are under,
from which it appears to me there is something which as yet has not
been accounted for, particularly in Binner Downs engines. A statement
was given to me by Captain Gregor, the chief agent and engineer of the
mine, which appears so plain that I cannot doubt the facts, though
they differ very widely from all former opinions. There are two
engines, one of 42 inches diameter, the other of 70 inches diameter,
10-feet stroke.
"Formerly those engines worked without cylinder cases, when the
70-inch cylinder burnt 1-1/2 wey of coal, and performed a regular duty
of forty-one millions; since that time brickwork has been placed round
the cylinder and steam-pipes, leaving a narrow flue, which is heated
by separate fires. These flues consume about 5 bushels of coal in
twenty-four hours; the heat is not so great as to injure the packing,
which stands good for thirteen weeks; the saving for several months
past has increased the duty to sixty-three millions.
"Before the use of this flue 108 bushels of coal were consumed under
the boiler, now only 67 bushels are needed, which with the 5 bushels
in the flue gives 72 bushels. The coal burnt under the boiler gives
a duty of sixty-six millions, or an expansion of 60 per cent. by the
heat of 5 bushels of coal in the flues, and a duty of 1781 millions
gained in twenty-four hours by 5 bushels of coal, which amounts to
350 millions gained by each of these 5 bushels. The 42-inch cylinder
is as near as possible under the same circumstances, no other
alterations have been made; and to prove this they left out the fires
in the flues, and the engines fell back to their former duty, and the
condensing water increased in the same proportion.
"The surface sides heated by this 5 bushels of coal is about 300
surface feet, the saving effected is 1781 millions, which is six
millions saving for each foot of surface on the castings in the flues.
In Wheal Towan engine that did eighty-seven millions, the surface
sides of the boiler was 1000 feet of fire-sides for every bushel of
coal burnt in an hour, and the duty performed per minute from each
foot of boiler fire-sides was 1500 lbs. 1 foot high. Now it appears
that the heating of Binner Downs 300 surface feet gave a saving of
6000 lbs. per minute per surface foot; whereas the boiler sides only
gave 1500 lbs. of duty per minute for each foot of boiler fire-sides.
Therefore the saving by heating the sides of the cylinder is equal
to four times the duty done by each square foot of boiler sides;
and further, it appears that the 300 feet, when not heated, though
clothed round with brickwork, condensed or prevented from expanding
the steam of 41 bushels of coals, which was eight times as much steam
condensed as the 5 bushels of coal would raise. Now if this be a
report of facts, which I have no reason to doubt (but still I will be
an eye-witness to it next week), there must be an unknown propensity
in steam above atmosphere strong to a very sudden condensation, and
_vice versâ_, to also a sudden expansion, by a small heat applied to
the steam-sides; and if by heating steam, independent of water, such a
rapid expansion takes place, certainly a rapid condensation must take
place in the same ratio, which might be done at sea by cold sides to a
great advantage, always working with fresh water.
"I shall have a small portable engine finished here next week, and
will try to heat steam, independent of water, in small tubes of iron,
on its passage from the boiler to the cylinder, and also try cold
sides for condensing.
"If the above statement prove to be correct, almost anything might
be done by steam, because then additional water would not be wanted
for portable engines, but partially condensed and again returned into
the boiler, without any fresh supply or the incumbrance of a great
quantity; and boilers might be made with extensive fire-sides, both
to heat water and steam, and yet be very light.
"It appears that this engine, when working without the heated flues
round the cylinder and pipes, evaporated 20,000 gallons of water into
steam, in twenty-four hours, more than when the flues were heated, and
the increase of condensing water was in the same proportion. It is so
unaccountable to me that I shall not be satisfied until I prove the
fact, the result of which I will inform you, and shall be very glad to
receive your remarks on the foregoing statement.
"The first engine that will be finished here for Holland will be a
36-inch cylinder, and a 36-inch water-pump, to lift water about 8 feet
high; on the crank-shaft there is a rag-head of 8 feet diameter, going
8 feet per second, with balls of 3 feet diameter passing through the
water-pump, which will lift about 100 tons of water per minute. It
is in a boat of iron, 14 feet wide, 25 feet long, 6 feet high, so as
to be portable, and pass from one spot to another, without loss of
time. It will drain 18 inches deep of water (the annual produce on the
surface of each acre of land) in about twenty minutes for the drainage
of each acre, with one bushel or sixpennyworth of coal per year. The
engine is high pressure and condensing.
"I remain, Sir,
"Your very humble servant,
"RICHARD TREVITHICK.
"P.S.-Woolf is making an apparatus to throw back from the bottom of
the cylinder on to the top of the piston a fluid metal every stroke.
He says he proved by an indicator that he raised 18,000 inches of
steam from 1 inch of water, of 11 lbs. to the inch pressure on a
vacuum, and that the reason why this engine did not do 300 millions,
was because the steam passed by the sides of the piston. That an
engine at the Consolidated Mines working 10 feet 2 inch stroke, going
7/8ths expansive, beginning with steam of 20 lbs. to the inch above
the atmosphere, and ending with 11 lbs. on a vacuum. I doubt this
statement; however, there is some hidden theory as yet, because
some engines perform double as much as others, under the same known
circumstances, and I believe that nothing but practice will discover
where this defect is, for, in my opinion, no statement of theory
yet given is satisfactory why high-pressure engines so far exceed
low-pressure engines. It is facts that prove it to be so, therefore
all theory yet laid down must be defective."
[Illustration: MOUNT'S BAY. [W. J. Welch.]]
At the date of this letter Trevithick had been rather more than a year
in England, residing generally at Hayle, within half-a-dozen miles of
Mount's Bay, from which he had sailed for America; and after eleven
years of wandering in countries where steam-engines were unknown,
except those that he himself had constructed, was again on his return
giving his whole thoughts to the idol of his life.
During that period scientific men in Europe thought and wrote much
on the question of relative temperature, pressure, economy, and
manageability of steam. Newcomen's great discovery a century before
was the avoidance of the loss of heat by the cooling at each stroke
of the exterior of the steam-vessel of Savery's engine by injecting
cold water into the steam in the cylinder. After fifty years came the
Watt improvement, still reducing the loss of heat by removing the cold
injection-water from the steam-cylinder to a separate condenser.
The high-pressure steam-engine was perfect without injection-water,
though when convenient its use was equally applicable as in the
low-pressure engine. Trevithick, on his return to civilized life, read
the views of Watt on steam, as given in 'Farey on the Steam-Engine.'
On informing Davies Gilbert of his doubts of the accuracy of those
views, and of his intention of testing them by comparison with the
work performed by Cornish pumping engines, his friend, who had just
published his 'Observations on the Steam-Engine,'[158] forwarded a copy,
from which the following is an extract:--
[Footnote 158: 'Observations on the Steam-Engine,' by Davies Gilbert,
V.P.R.S., January 25th, 1827. See 'Philosophical Transactions.']
"One bushel of coal, weighing 84 lbs., has been found to perform
a duty of thirty, forty, and even fifty millions, augmenting with
improvements, chiefly in the fire-place, which produce a more rapid
combustion with consequently increased temperature, and a more
complete absorption of the generated heat; in addition to expansive
working, and to the use of steam raised considerably above atmospheric
pressure."
Those words gave the result of Trevithick's experience made known to
his friend during twenty years of labour,[159] and yet by a seeming
fatality his name is not found in his friend's book.
[Footnote 159: See letter, vol. ii., p. 143.]
Sir John Rennie, who in youth had been employed under Boulton and Watt
at Soho, and had risen to be a member of the Royal Society, came about
that time into Cornwall, at the request of the Admiralty, to make
examination into the work performed by Cornish pumping engines, and
selected Wheal Towan engine on which to make special experiments.[160]
The subject of Trevithick's note was therefore at that period, and
still is, a matter of importance; and his practical treatment of
the question is more instructive to young engineers than complex
rules. Arthur Woolf was at the same time experimenting on steam at
the Consolidated Mines, and finding the want of agreement between
the rules of low-pressure and the practice of high-pressure engines,
imputed the error to the escape of steam by the sides of the piston.
Trevithick disbelieved this, "because some engines perform double as
much as others, under the same known circumstances," and advocated
the observance of general practice to prove why high-pressure engines
were more economical than those of low-pressure. Captain Gregor had
placed fire-flues around the steam cylinder and pipes, hoping thereby
to exceed the duty of the Wheal Towan engine, whose boiler, cylinder,
and steam-pipes were carefully clothed with a thick coating of sawdust
or other non-conductor of heat, and lifted eighty-seven millions of
pounds of water 1 foot high by the heat from a bushel of coal weighing
84 lbs. This was the greatest duty that had ever been recorded from a
steam-engine. The Trevithick or Cornish boilers, similar to those in
Dolcoath,[161] measured at the rate of 1000 superficial feet of heating
surface for each bushel of coal burnt in an hour, and in round numbers
gave a duty of 1500 lbs. lifted a foot high to each foot of boiler
surface. In words not technical, the heat from 1 lb. of coal gave steam
that raised 460 tons weight of water 1 foot high.
[Footnote 160: See vol. ii., p. 185.]
[Footnote 161: See drawing, vol. ii., p. 169.]
The cylinder of this engine used the Watt steam-jacket. The Binner
Downs engine was doing not one-half this duty, namely, forty-one
millions; when brick flues were built around the cylinder, cylinder
cover, and steam-pipes, and one or two fire-places, fixed near the
bottom of the cylinder, of a size to conveniently burn 5 bushels of
coal in twenty-four hours, the heat from which circulated through those
flues on its way to the chimney, and increased the duty of the engine
by one-half, raising it to sixty-three millions; in other words, during
twenty-four hours of working, 67 bushels of coal in the boiler, and 5
bushels in the cylinder flues, did the same work as 108 bushels in the
boiler without the cylinder flues, causing a saving of fifty per cent.
by their use. Another startling fact was the greater effect for each
foot of heating surface in the steam-cylinder flues than in the boiler
flues; the latter gave a power of 1500 lbs. raised 1 foot high by a
bushel of coal, while the former gave 6000 lbs. of power from the same
amount of coal and heating surface.
Here was a mystery that Trevithick would not believe until he had
seen it with his own eyes: he searched for it for a year or two, and
overlooking the fact that the more simply arranged engine of his once
pupil, Captain Samuel Grose, was doing more duty than the superheating
steam-engine at Binner Downs, he worked at what seemed to be new
facts, and converted them into a new engine.
We have traced how succeeding engineers tried to prevent loss of heat.
Trevithick took the first bold step, and aiming at the same object,
made the boiler the steam-jacket for the cylinder, and in his patent
of 1802 went still further and protected the boiler from external
cold, and thus describes it:--"The steam which escapes in this engine
is made to circulate in the case round the boiler, where it prevents
the external atmosphere from affecting the temperature of the included
water, and affords by its partial condensation a supply for the boiler
itself."[162] So that a quarter of a century before the date of those
Binner Downs experiments he had patented an engine having neither
cylinder nor boiler exposed to the cooling atmosphere. The flues around
the Binner Downs cylinder were difficult of control. Trevithick says
the piston packing had not been injured, showing that observers thought
it would be, and even the cylinder was endangered, for the writer,
who stoked those heating flues, recollects the fires burning very
brightly in them. The ready transmission of heat through thin metal,
used by Trevithick in 1802 for heating feed-water, and in the cellular
bottom of the iron ship of 1808, serving as a surface condenser,[163]
and his experience in 1812, that "the cold sides of the condenser
are sufficient to work an engine a great many strokes without any
injection,"[164] still followed up in 1828 by condensing steam without
the use of injection-water, led to what is since known as Hall's
surface condenser.
[Footnote 162: See patent specification, vol. i., p. 132.]
[Footnote 163: See vol. i., p. 335.]
[Footnote 164: See Trevithick's letter, 7th December, 1812, vol. ii., p.
18.]
The following letter is in the handwriting of the present writer;
it is the only one of Trevithick's numerous letters not written by
himself:--
"MR. GILBERT, "HAYLE, _December 30th, 1828_.
"Sir,--On the 28th inst. I received your printed report on steam, and
have examined Farey's publication on sundry experiments made by Mr.
Watt, which are very far from agreeing with the actual performance
of the engines at Binner Downs. Mr. Watt says that steam at one
atmosphere pressure expands 1700 times its own bulk as water at 212°,
and that large engines ought to perform eighteen millions when loaded
with 10 lbs. to the inch of actual work, the amount of condensing
water being one-fortieth part of the content of the steam in the
cylinder at one atmosphere strength, the cold condensing water at 50°,
and when heated 100°. This would give for the Binner Downs engine,
with a 70-inch cylinder, 10-inch stroke, 11 lbs. effective work on the
inch (this load being one-tenth more than in Watt's table, by Farey,
for an engine of this size and stroke), 57 gallons of injection-water
for each stroke, and when working eight strokes per minute, to do
eighteen millions would consume 11-1/4 bushels of coal per hour.
"Now the actual fact at Binner Downs, at the rate of working and power
above mentioned, is that 3 bushels of coal per hour were burnt, using
13 gallons of injection-water at each stroke at 70° of heat, which was
raised by its use to 104°, or an increase of 34°, which, multiplied by
13 gallons, gives 442. Mr. Watt's table for this engine and work gives
57 gallons of condensing water at 50°, heated by use to 100°. This 50°
raised, multiplied by the 57 gallons of water, amounts to 2850, or six
and a half times the quantity really used in the Binner Downs engine,
and nearly four times the coal actually used at present. Mr. Watt
further says that steam of 15 lbs. to the inch, or one atmosphere,
from 1 inch of water at 212° occupies 1170 inches, and that steam of
four atmospheres, or 60 lbs. to the inch, gives only 471 inches at a
heat of 293°. Now deducting 50° from 212° leaves 162° of heat raised
by the fire. Multiply 15 lbs. to the inch by 1700 inches of steam,
and divide it by 162°, gives 138°, whereas if you deduct 50° from
293°, it leaves the increase of heat by the fire 243°. Steam of 60
lbs. to the inch multiplied by 471, being the inches of steam made
by 1 inch of water divided by 243°, the degrees of heat raised by the
coal, gives a product of 116; therefore, by Mr. Watt's view it appears
that low steam would do one-fifth more duty than high steam, and yet
Binner Downs engine in actual work performs about four times the duty
given by Mr. Watt's theory and practice, with only one-sixth part of
the amount of heat carried off by the condensing water, proving that
high steam has much less heat, in proportion to its effective force;
and this is further proved by the small quantity of condensing water
required to extract its heat.
"Yesterday I proved this 70-inch cylinder while working with the
fire-flues round it, which flues only consumed 5 bushels of coal in
twenty-four hours. The engine worked eight strokes a minute, 10-feet
stroke, 11 lbs. to the inch effective force on the piston; steam in
the boiler 45 lbs. above the atmosphere, consuming 12 bushels of
coal in four hours, using 13 gallons of condensing water at each
stroke, which was heated from 70° to 104°; but when the fires round
the cylinder were not kept up, though still having the casing of hot
brickwork around it, and performing the same work, burnt 17 bushels
of coal in the same time of four hours, and required 15-1/2 gallons
of condensing water, which was heated from 70° to 112°. You will find
that the increased consumption of coal, by removing the fire from
around the cylinder, was nearly in the same proportion as the increase
and temperature of the condensing water, showing the experiment to be
nearly correct.
"From the general reports of the working of the engines it appears
that when the surface sides of the castings are heated, either by hot
air or high steam, the duty increases nearly fifty per cent. from this
circumstance alone.
"A further proof of the more easy condensation of high steam was in
the Binner Downs 42-inch cylinder engine, 9-feet stroke, six strokes
per minute, 11 lbs. effective power on each inch, burning 1-1/3
bushel of coal an hour. In this engine the proportion of saving by
the heating flues was the same as in the large engine. I tried to
condense the steam by the cold sides of the condenser, without using
injection-water. The water in the condenser cistern was at 50°.
After working for twenty-five minutes the small quantity of hot water
discharged at the top of the air-pump reached 130° of heat, but then
would rise no higher, the cold sides of the condenser being equal to
the condensation of all the steam. The eduction-pipe and air-pump,
with its bottom and top, gave 60 feet of surface sides of thick
cast iron, and about 20 feet more of surface sides of a thin copper
condenser; altogether, 80 feet of surface cold sides, surrounded by
cold water. About half a pound on the inch was lost in the vacuum, the
discharged water being 130° of heat instead of 100°. The vacuum was
made imperfect by about 1-1/2 lb. to the inch.
"It is my opinion that high steam will expand and contract with a much
less degree of heat or cold in proportion to its effect, than what
steam of atmosphere strong will do. I intend to try steam of five
or six atmospheres strong, and partially condense it down to nearly
one atmosphere strong, and then by an air-pump of more content than
is usual to return the steam, air, and water, from the top of the
air-pump, all back into the boiler again, above the water-level in
the boiler, and by a great number of small tubes, with greatly heated
surface sides, to reheat the returned steam; though by this plan I
shall lose the power of the vacuum, and also the power required on the
air-bucket to force the steam and water back again into the boiler,
yet by returning so much heat I shall over-balance the loss of power,
besides having a continued supply of water, which in portable engines,
either on the road or on the sea, will be of great value.
"I shall esteem it a very great favour if you will be so good as to
turn over in your mind the probable theory of those statements, and
give me your opinion. If Mr. Watt's reports of his experiments are
correct, how is it possible that the high-pressure engine that I built
at the Herland thirteen years ago, which discharged the steam in open
air, did more than twenty-eight millions? If you wish, I will send a
copy of the certificate of the duty done by this engine, which states
very minutely every circumstance. Now that cylinder, with every part
of the engine, was exposed to the cold; had it been heated around
those surfaces, as on the present plan, it would have done above forty
millions.
"Suppose the Binner Downs 70-inch cylinder engine, 10-feet stroke,
working with full steam to the bottom of the stroke, when, by the
experiment, the heated flues were again laid on would have worked
one-third expansive, by the heat of 5 bushels of coal around the
cylinder. Now one-third of the power would make a 3 feet 4 inch
stroke, 11 lbs. to the inch effective power, eight strokes a minute,
during twenty-four hours, by the consumption of 5 bushels of coal
applied on the surface sides of the cylinder, performing a duty of 324
millions with a bushel of coal. Now suppose the cylinder without the
heating flues had the steam cut off at two-thirds of the stroke, and
that it is possible in a moment to heat the cylinder by the flues; in
that case the steam would, by its expansion from the hot sides, fill
the last third of the cylinder to the bottom of the stroke; then if
that steam could be suddenly cooled, so as to contract it one-third,
the piston would ascend one-third its stroke in the cylinder; and it
appears in theory by this plan, that a cylinder once filled two-thirds
full of steam, by receiving the heat on its surface sides from 5
bushels of coal, and again suddenly cooling down, would continue to
work for ever, without removing the steam from the cylinder, and
would perform a duty of 324 millions. This never can be accomplished
in practice in this way, but the effect may be obtained by partially
condensing in a suitable condenser, and again heating by hot sides.
"This mystery ought to be laid open by experiment, for what I have
stated are plain facts from actual proofs, and I have no doubt that
time will show that the theory of Mr. Watt is incorrect. Though there
were 300 feet of cold sides, yet 200 feet were not condensing steam,
because on the return of the piston, what was condensed below, and
while the engine was resting, did not make against it more than what
was condensed above the piston on its descent; therefore you may count
on 150 feet of cold external sides constantly condensing, that made
this third-part difference against the expansion of the steam.
"I remain, Sir,
"Your very humble servant,
"RICHD. TREVITHICK."
The writer's note-book used during those experiments is in his
possession, as well as Trevithick's note-book giving particulars of
experiments at several mines, from which the following extracts are
taken:--
"CORNWALL, _August, 1828_.--Wheal Towan 80-inch cylinder,
10-feet stroke, 6·9 strokes per minute, loaded to 9·5 lbs. on the inch
of the piston, with three of Trevithick's boilers, each 37 feet long,
6 feet 2 inches diameter, with fire-tube 3 feet 9 inches diameter,
fire-place 6 feet long, evaporated 13 square feet of water with 1
bushel of coal,[165] duty 87 millions. The heat in the stack was just
the same as the heat of the steam in the boiler. Another engine of
the same size on the same mine, with similar boilers, but working
only 4·06 strokes per minute, loaded to 4·55 lbs. on each inch of the
piston, did 50·8 millions.
[Footnote 165: 84 lbs.]
"Wheal Vor 53-inch cylinder, 9-feet stroke, 6·59 strokes per minute,
loaded to 19·58 lbs. on each square inch of the piston, did 36·6
millions.
"Wheal Damsel 41-inch cylinder, 7 feet 6 inch stroke, 5·52 strokes per
minute, loaded to 21·5 lbs. on the inch of the piston, did 33 millions.
"It would appear, therefore, that about 10 lbs. to the inch on the
piston allows of the best duty, and that a 10-feet stroke exceeds in
duty a 7 feet 6 inch stroke.
"The Wheal Towan engine, doing 87 millions, had 1248 feet of tube
fire-surface, and a similar amount of external boiler surface in the
flues. 2-1/2 bushels of coal were consumed each hour, giving about
1000 feet of fire-sides for each bushel of coal consumed per hour, and
50 feet of fire-bars. Those boilers were intended to supply steam for
working the engine at ten strokes a minute; a bushel of coal an hour
would in that case have had 600 feet of boiler fire-surface.
"Binner Downs 70-inch cylinder, 10-feet stroke, did 41 millions. A
fire was then put around the cylinder and steam-pipes, which burnt 5
bushels of coal in twenty-four hours, by which the duty was increased
to 63 millions. The surface sides of the cylinder, cylinder-top,
and steam-pipes heated by flues was 300 feet, and caused a saving of
41 bushels of coal in twenty-four hours. Another engine in the same
mine was tried, having a 42-inch cylinder; when the fire was around
the cylinder, she worked 100 strokes without injection-water; the
expansion-valve was closed at half-stroke, the steam in the boiler 56
lbs. on the inch above the atmosphere."
It is not easy to deal with the important reasonings flowing from
those facts, and influencing the form and economy of the steam-engine,
nor to show if Trevithick was right in discrediting the laws laid
down by Watt. Newcomen's engine had the interior, as well as the
exterior of the steam-cylinder exposed to the cooling atmosphere.
Watt, by putting a cover on the cylinder, reduced the loss of the
heat from the interior, and by his steam-case hoped to reduce the
loss from the exterior, though by it he increased the amount of
surface exposed to the cold. In Trevithick's early engines the boiler
alone exposed heat-losing surface, and this was further reduced by
its own comparatively small size, the engine and boiler complete not
exposing one-quarter of the surface of a Watt low-pressure engine of
equal power. One object of the Binner Downs experiment was to further
curtail this loss of power by increasing the heat of the steam while in
operation in the cylinder, since called superheating steam.
This principle of giving increased heat to steam, after it had left
its state as water, was made practical by Trevithick's boiler at Wheal
Prosper in 1810, where the flues having first been carried around the
water portion of the boiler, then passed over the steam portion;[166]
and again in the upright boiler of 1815, having the upper end of the
fire-tube surrounded by steam above the water line.[167] Those early
beginnings of superheating steam and surface condensation culminated
in the Binner Downs experiments of 1828, one immediate practical result
of which was the tubular surface condenser, enabling steamboat boilers
to avoid, in a great measure, the use of salt water, facilitating in a
marked degree the application of marine boilers and engines with steam
of an increased pressure.
[Footnote 166: See vol. ii., p. 71.]
[Footnote 167: See vol. i., p 354.]
The Binner Downs engine, with a cylinder of 70 inches in diameter,
and a stroke of 10 feet when working with steam in the boilers of 45
lbs. to the square inch above the atmosphere, and using the heating
flues around the cylinder, required 13 gallons of injection-water at
each stroke, and consumed at the rate of 3 bushels of coal an hour, to
produce a duty equal to eighteen millions; by removing the cylinder
superheating flues, the quantity of injection-water for the same amount
of work increased to 15-1/2 gallons, and the coal to 4-1/4 bushels.
Watt's rule for his low-pressure steam vacuum engine doing a duty of
eighteen millions, gave 57 gallons of injection-water, and 11-1/4
bushels of coal.
On the question of coal, this statement agrees very nearly with
Trevithick's letters of sixteen years before, when he used the
high-pressure boilers in the Dolcoath pumping engine,[168] promising that
his high-pressure expansive engine would do the work with one-third of
the coal required in the low-pressure vacuum engine.
[Footnote 168: See vol. ii., p. 171.]
The high-pressure steam required a less amount of injection-water to
condense it than the low-pressure steam, in proportion to the work
done, showing the Watt rule and the Watt experience to be inapplicable
to high-pressure engines; for instead of 57 gallons of injection-water
the Binner Downs engine with steam of 45 lbs. to the inch required
but 15-1/2 gallons of injection-water, and this amount was further
reduced to 13 gallons by superheating the steam; this roughly agrees
with the coal consumed, or in other words, with the amount of heat
to be carried off by injection-water: the Watt rule giving 11-1/4
bushels as the fair allowance for low-pressure steam vacuum engines,
while the high-pressure steam vacuum engine burnt but 4-1/4 bushels.
This was further reduced to 3 bushels by superheating. Those facts led
to the idea that if the steam pressure was sufficiently increased,
condensation might be carried out without any injection-water, by
the transmission of the heat in the steam through the metal sides
of the condenser. An experiment was at once made by removing the
Watt condenser and injection-water, as he had done seventeen years
before,[169] using in their stead a thin copper surface-condenser
immersed in cold water, producing, within 1/2 lb. on the inch, as good
a vacuum as when injection-water was used, leading to the conclusion,--
[Footnote 169: See Query 3rd, vol. ii., p. 19.]
"It is my opinion that high steam will expand and contract with a much
less degree of heat or cold, in proportion to its effect, than what
steam of atmosphere strong will do. I intend to try steam of five or
six atmospheres strong, and partially condense it down to nearly one
atmosphere strong, and then by an air-pump of more content than is
usual to return the steam, air, and water back into the boiler again,
and by a great number of small tubes, with greatly heated surface
sides, to reheat the returned steam."
This, in practical words, is the surface condenser by which the used
steam is returned to the boiler in the form of water. The more general
use of high-pressure steam of 70 or 90 lbs. to the inch, increasing its
expansive force on one side of the piston by superheating it on its
passage through numbers of small tubes, and decreasing its expansive
force on the other side of the piston by cooling it in passage through
similar tubes exposed to cold, is partly effected in steamboats, but
has not yet been attempted in engines on the road.
After a month's further consideration he wrote:--
"Wheal Towan engine is working with three boilers, all of the
same size, and the strong steam from the boilers going to the
cylinder-case; the boilers are so low as to admit the condensed
water to run back from the case again into the boiler: they find
that this water is sufficient to feed one of these boilers without
any other feed-water, therefore one-third of the steam generated
must be condensed by the cold sides of the cylinder-case, and this
agrees with the experiments I sent to you from Binner Downs. Wheal
Towan engine has an 80-inch cylinder, and requires 72 bushels of
coal in twenty-four hours, therefore, the cylinder-case must, in
condensing high-pressure steam, use 24 bushels of coal in twenty-four
hours. Boulton and Watt's case for a 63-inch cylinder working with
low-pressure steam, condensed only 4-1/2 bushels of coal in equal
time, the proportions of surface being as 190 to 240 in Wheal Towan.
Nearly five times the quantity was condensed of high steam than of low
steam, proving that there is a theory yet unaccounted for."[170]
[Footnote 170: See Trevithick's letter, January 24th, 1829, vol. ii., p.
368.]
These apparent facts are, in the case of steamboats, more culpably
overlooked now than when he wrote forty-two years ago; engines have
been examined and reported on by eminent scientific men, but it was
left for Trevithick to point out that cold on the surface of the
steam-case of a Watt low-pressure steam vacuum engine condensed about
one-fifteenth of the steam given from the boilers, and that the loss
from exposure to cold was nearly five times more from high-pressure
steam than from low-pressure. Within a few more months he determined
on constructing an engine for the purpose of more accurately testing
those views.
"MR. GILBERT, "HAYLE FOUNDRY, _July 27th, 1829_.
"Sir,--Below you have a sketch of the engine that I am making here for
the express purpose of experimenting on the working the same steam and
water over and over again, heating the returned steam by passing it in
small streams up through the hot water from the bottom of the boiler.
The boiler is 3 feet in diameter, standing perpendicular; the interior
fire-tube is 2 feet in diameter; there is a steam-case round the
outside of the boiler with a 1-1/2-inch space. This keeps the boiler
hot and partially condenses the steam before it is again forced into
the boiler.
[Illustration]
"The boiler is 15 feet high; the cylinder 14 inches diameter, with a
6-feet stroke, single power. The pump for forcing the steam and water
back again is 10 inches in diameter, with a 2 feet 9 inch stroke,
about one-quarter part of the content of the steam-cylinder. The
bottom of the boiler will have a great number of small holes, about
1/16th of an inch in diameter, through which the steam delivered into
the boiler will pass up through the hot water, by which I should
think it will heat those small streams of steam again to their usual
temperature.
"The pump for lifting water to prove the duty of the engine is 30
inches in diameter, with a 6-feet stroke, but this may be lengthened
to a 12-feet lift, as the trial or load in the experiments may
require, giving from 12 to 24 lbs. to the inch in the piston. This
machine will be ready before your return to Cornwall, and I intend to
prove it effectually before I go to Holland.
"The Holland engine lifted on the trial, when they came down to see
it, 7200 gallons of water a minute 10 feet high with 1 bushel of coal
an hour; exceedingly good duty for a small engine of 24-inch cylinder,
being 34,560,000 of duty.
"On the 17th August the trial comes on between the two companies
about the quays. They are as desperate as possible on both sides,
and castings and every other article are thrown down to 30 per cent.
below cost price; iron pumps for 6_s._ 6_d._ per cwt., and coal sold
to the mines for 37_s._ 3_d._ per wey, when 48_s._ per wey on board
ship was paid for it. Several thousands lost per year by each party.
This never can last long. If you can think of any improvement I shall
be very glad to hear in time, before it may be too late to adopt it.
At all events, if it is not too much trouble to write, I shall be very
glad to hear from you. What effect do you think the water will have
in heating the steam on its passage to the top of the water from the
false bottom of the boiler?
"I have a cistern of cold water, with a proper condenser in it,
connected between the bottom of the boiler-case and the force-pump
to the bottom of the boiler, therefore I can partially condense by
cold water sides, or by cold air sides just as I please, by rising or
sinking the water in the cistern.
"The boiler is made very strong to try different temperatures, and
an additional length to the water-pump makes all very suitable for a
great number of experiments, and if there is any good in the thing I
will bring it out.
"I shall have indicators at different places to prove what advantages
can be gained. I hope to have the pleasure of your company during
those experiments, which I think will throw more light on this
subject than ever has yet been done. Some trials since I last wrote
to you make me very confident that much good will arise from these
experiments, but to what extent is uncertain.
"I remain, Sir,
"Your most obedient servant,
"RICHARD TREVITHICK."
Trevithick did not use letters to illustrate his sketch, knowing that
Davies Gilbert would comprehend it; but the reader of to-day may not
find it so easy, therefore the writer has added them with a slight
detail description, he having been Trevithick's daily companion when
those drawings and experiments were made. _a_, top of boiler; _b_,
water line; _c_, centre of wheel; _d_, cast-iron wheel and chain; _e_,
chimney, 13 in. in diameter; _f_, fire-tube, 2 ft. diameter; _g_, outer
boiler-*case, 3 ft. diameter, 15 ft. long; _h_, water space of 6 in.;
_i_, boiler steam-case, 3 ft. 4 in. diameter; _j_, small holes through
which steam and water are forced into the boiler; _k_, force-pump, 10
in. diameter, 2 ft. 9 in. stroke; _l_, steam-cylinder, 14 in. diameter,
6-ft. stroke; _m_, piston-rod; _n_, fire-door; _o_, fire-bars; _p_,
pump for testing the power of the engine.
There is a natural tendency in men of genius to unwittingly return,
under new forms, to old ideas. The ideas are similar, though in
combination with new forms and new acquirements; even the outline of
this 1828 boiler, with the exception of its outer steam-casing, is
very like that in a letter to Davies Gilbert fourteen years before,[171]
of which Trevithick had kept no copy. When in the foregoing letter
he wrote, "There is a steam-case round the outside with a 1-1/2-inch
space; this keeps the boiler hot and partially condenses the steam
before it is again forced into the boiler," he had forgotten that
twenty-seven years before, when constructing his first high-pressure
steam-engines, he thus specified his invention:--"The steam which
escapes in this engine is made to circulate in the case round the
boiler, where it prevents the external atmosphere from affecting
the temperature of the included water, and affords by its partial
condensation a supply for the boiler itself."[172]
[Footnote 171: See Trevithick's letter, 7th May, 1815, vol. i., p. 364.]
[Footnote 172: See patent specification of 1802, vol. i., p. 128.]
Not one of his numerous patent specifications has been found among his
papers, neither do his letters refer to them; probably he never read
them after the first necessary examinations.
"MR. GILBERT, "HAYLE FOUNDRY, _November 5th, 1829_.
"Sir,--The engine has been worked. The result is ten strokes per
minute, 6-feet stroke, with half a bushel of coal per hour, lifting
six thousand pounds weight. This was done with water in the cistern
round the condenser, which water came up to 180 degrees of heat, and
remained so. The water sides of the condenser covered with this hot
water was 50 surface feet. I tried it to work with the cold air sides,
but I found that the cold air sides of 120 feet would only work it
four strokes per minute. I should have worked the steam much higher
than 50 lbs. to the inch, but being an old boiler I thought it a risk.
I am now placing an old boiler of 350 feet of cold sides more to the
condenser, to give a fair trial to condensing with cold sides alone.
The steam below the piston was about 6 or 7 lbs. to the inch above
the atmosphere. The force-pump to the boiler was about one-fifth part
of the content of the cylinder, and the valve close to the boiler
lifted when the force-piston was down about two-thirds of its stroke,
at which time the returned steam entered the boiler again. I have
no doubt of doing near ten times the duty that is now done on board
ships, without using salt water in the boiler, as at present. Our
boiler has been working three days and the water has not sunk 1 inch
per day. I am quite satisfied the trial will be a great success.
"Mr. Praed and Sir John St. Aubyn are anxious to get a high bank
carried out from Chapel Angel to 15 feet below low-water mark on the
bar, to make Hayle a floating harbour.
"I have proposed to make a sand-lifting engine. When I built that
engine for deepening Woolwich Harbour, we lifted 300 tons per hour
through 36 feet of water, and 20 feet above water, 56 feet above the
bottom. This was done with two bushels of coal per hour, therefore it
will not cost above one penny per square fathom to lift the sand over
this embankment. It is intended to get down Mr. Telford to give his
opinion on it. Your remarks on it would be of service.
"I remain, Sir,
"Your humble servant,
"RICHARD TREVITHICK."
The writer having worked at these experiments, knows that their
object was to employ high-pressure steam in the boiler, using it very
expansively in the cylinder, and by cold surface sides reducing its
bulk either to low-pressure steam or boiling water, and then force it
again into the boiler.
"MR. GILBERT, "HAYLE FOUNDRY, _November 14th, 1829_.
"Sir,--I have both of your letters and sketches, which shall be put
in hand. I understand it perfectly well. Since I wrote to you last
I have made several satisfactory trials of the engine, and think it
unnecessary to make any further experiments. The statement below may
be depended on for a future data. The load of the engine was 6280
lbs., being 20 lbs. to the inch for a 20-inch cylinder with a 6-feet
stroke, 12 strokes per minute, with three-quarters of a bushel of
coals per hour, giving a duty of 361,728,000 for 1 bushel of coal, a
duty far beyond anything done in the county by so small an engine. The
cold water sides round the condenser was 60 feet, and the water at 112
degrees temperature, not having a sufficient stream of cold water to
supply the cistern. Each foot of cold water sides did 7536 lbs. per
minute, about three times the work done in the county per foot of hot
boiler sides; therefore the condenser need not be more than one-third
of the boiler sides. By making the condenser of 4-inch copper tubes
and of an inch thick, it would stand in one-twentieth part of the
space of the boiler.
"I put a boiler naked to try cold air sides; it was very rusty, and
did not condense as fast as I expected. The engine worked exceedingly
well, but slow. The duty performed for each foot of cold air sides
was 565 lbs. per minute, about one-thirteenth part of the condensing
of cold water sides. We never wanted to get the steam above 60 lbs. to
the inch. I have no doubt but that copper pipes of 1/32nd of an inch
thick, clean and small, would do considerably more, because the hot
water that came out of the boiler from the condensed steam was but 170
decrees, and the external sides the same heat when the steam was 15
lbs. above the atmosphere in the condensing boiler. This boiler was 4
feet 6 inches diameter, and I think that towards the external sides of
the boiler there was a colder atmosphere, if I may call it so, than
what it was in the middle of this large condensing boiler, because I
found by trying a small tin tube, that it would condense 1500 lbs. for
each foot of cold air sides.
"However, as it is, it will do exceedingly well for portable purposes.
"The duty, I doubt not, will be, both for water and air sides
condensing, at least 50 per cent. above our Cornish engines, which
will be above four times what is now done with ships' engines,
especially when you take into consideration their getting steam from
salt water, and letting out so much water from the boiler to prevent
the salt from accumulating in the boiler, which will make 30 per cent.
more in its favour.
"If strong boilers to stand 200 lbs. to the inch are made with small
tubes, I have no doubt but that the duty would be considerably more,
and my engines will not be one-quarter part of the weight, price, or
space of others; and when every advantage is taken it will be 1000 per
cent. superior in saving of coal to those now at work on board. This
engine works well, and returns the steam very regularly every stroke
into the boiler.
"I am extremely sorry you were not present to see these experiments.
Please make your remarks on these statements, with any further
information you may judge useful.
"I shall now make drawings agreeable to my experiments for actual
performance on board ships. In hope of hearing from you soon,
"I remain, Sir,
"Your very humble servant,
"RICHD. TREVITHICK."
The large old boilers used as surface condensers, in which the steam
was partially condensed by the transmission of heat to the external
atmosphere, together with its further condensation in a smaller
condenser with cold water around it, so reduced its expansiveness,
that a large feed-pump drew the hot water and steam from the small
condenser, and forced it back into the boiler without any reduction of
quantity; those temporary contrivances, almost immediately resolved
themselves into a condenser made of copper tubes surrounded by cold
water.
Having proved by six months' experiment on a working scale the
practicability of the plan which in reality he had invented twenty
years before in the iron steamship,[173] he wrote in June, 1830:--
[Footnote 173: Drawing of iron steamship, vol. i., p. 336.]
"TO THE RIGHT HONOURABLE THE LORDS COMMISSIONERS OF THE
ADMIRALTY, &c., &c., &c.
"MY LORDS,
"About one year since I had the honour of attending your honourable
Board with proposed plans for the improvement of steam navigation,
and as you expressed a wish to see it accomplished, I immediately
made an engine of considerable power for the express purpose of
proving by practice what I then advanced in theory. I humbly request
your lordships will grant me the loan of a vessel of about 200 or
300 tons burthen, in which I will fix at my own expense and risk an
engine of suitable power to propel the same at the speed required:
no alterations whatever in the vessel will be necessary. When under
sail the propelling apparatus can be removed, and when propelled by
steam alone, the apparatus outside the ship will scarcely receive any
shock from a heavy sea. This new invention entirely removes the great
objection of feeding the boiler with salt water."
This petition was backed by Mr. Gilbert and Mr. George Rennie. His old
friend Mr. Mills took an interest in it, and wrote, "I am going to meet
Captain Symonds at Woolwich again to-morrow, and hope to be able to
persuade him to use his influence with Sir T. Hardy,"
"LAUDERDALE HOUSE, HIGHGATE,
"MR. GILBERT, "_August 19th, 1830_.
"Sir,--The boiler with the fire-place, cold air tubes outside the
boiler but within the steam-case, fire-tubes in the boiler from the
top of the fire-place to the top of the boiler, the ash-pit close,
except a small door to clear out the ashes.
[Illustration: FIG. 1.--PLAN SECTION.]
[Illustration: FIG. 2.--ELEVATION SECTION.[174]]
[Footnote 174: _a_, steam-case; _b_, boiler-case; _c_, space for
condensation of steam; _d_, water and steam space; _e_, fire-tubes;
_f_, fire-box; _g_, fire-door; _h_, fire-bars; _i_, ash-box; _j_,
ash-box door; _k_, air-tubes in condenser; _l_, chimney; _m_, water
level; a smoke-jack fan draught.]
"The design is for the cold air to pass down from the top of the
boiler through the air-tubes within the steam-case surrounding the
boilers, becoming heated in its passage by condensing the steam in the
case, and then to pass up through the fire-bars in, the hot state,
nearly as hot as the steam in the case; because this air, heated to
nearly 212 degrees by condensing the steam in its passage without any
of its oxygen being burnt, it will not carry off so much heat from the
fire as cold air would, and still have the same oxygen as cold air to
consume the coal.
"The cold air will be passing down the steam-case in the air-tubes,
and up through the fire and fire-tubes in the boiler. I find by
experiments I have made here, by placing a tin tube 2-1/2 inches in
diameter, 4 feet long, inside a 4-inch tube of the same length, having
boiling water and steam between the tubes, kept hot by a fire round
the outer tube, with a smith's bellows blowing in at the bottom of
the inside tube, having 2-2/3rds surface feet of condensing sides,
measuring the inside, where the air is passing up from the bellows,
heats from 60 to 134 degrees 15 square feet of cold air per minute.
When you compare the effective heat of 74 degrees given to 15 cubic
feet of air every minute from 2-2/3rds surface feet of tin plate, and
the heat contained in 15 cubic feet of air charged with 74 degrees of
effective heat, compared with steam of atmosphere strong, you will
find that the condensing power of surface sides is very great, and for
locomotive purposes might be carried still further, by forcing the air
more quickly through the tubes. If the statements on air given in some
books that I have read are correct, that there is about three times
as much heat in 1 gallon of steam of atmosphere strong as there is in
1 gallon of air of 212 degrees of heat, in that case 1 surface foot
of tin-plate sides of this pipe, by sending off the hot air before
described, would take out the heat of 1-1/2 cubic foot of steam per
minute of atmosphere strong, which in the common condensing engine
would be equal to a duty of 2700 lbs. lifted 1 foot high per minute;
but in the high-pressure expansive engine, the heat of 1-1/2 cubic
foot of steam would give a duty of 10,800 lbs., or four times the duty
of the Boulton and Watt engine.
"If you calculate on the air being heated to nearly 212 degrees before
it enters the fire, together with the heat given to the sides of the
boiler, the fuel saved will be above one-half on what has been done
by the high-pressure engines in Cornwall, because at present the coal
must pay for heating the cold air, therefore a less proportion goes
through the sides of the boiler, and is lost through the chimney;
whereas if the heat of the steam, by passing into the cold air, on
its way through the condenser tubes, is carried into the fire-place,
one-half of the coal must be saved; and you will find by calculation
that the quantity of air required to burn the coal, and also to
condense the steam, goes exactly in proper proportion for each other,
and for locomotive engines with a blast will go hand-in-hand almost
to any extent, and the size of an engine, for its power, is a mere
nothing.
"A smoke-jack fan in the ash-pit under the fire-bars, worked by the
engine, would draw air down the condensing tubes, and force it up
through the fire and fire-tubes always with the speed required, as the
steam and the condensation would increase in the same ratio.
"As it is possible to blow so much cold air into a fire as to put it
out, by first heating the air it would burn all the stronger, and
whatever heat is taken out of the condenser into the fire-place from
the steam that has been made use of, half this extra heat will go
into the boiler again, or in other words, but half the quantity of
cold will be put into the fire, being the same in effect as saving
fuel. Taking heat from the condenser through the boiler sides is an
additional new principle in this engine. I find by blowing through
tubes that the condensation of a surface foot of air-tube against a
surface foot of boiler fire-tube is greater than the fire that passes
through the boiler sides, where the common chimney draught is used, by
nearly double; but I expect when both air and fire tubes are forced
by a strong current of air it will be nearly equal, and the increase
of steam and of condensation can be increased by an increased current
of air, so as to cause a surface foot of fire and of air sides to do
perhaps five times as much; and of course the machine will be lighter
in proportion. I think air sides condensation preferable to water
sides, as so small a space does the work, and is always convenient,
and its power uniformly increasing with its speed, by the increased
quantity of air, without the weight of water vessels. This kind of
engine can be made to suit every place and purpose, and I think such
an engine of the weight of a Boulton and Watt engine will perform
twenty times the duty.
"Air sides condensation will be advantageous on board ship, because
there are holes for the passage of water through the bottom and sides
of the ship.
"I am anxious to have your opinion on this plan of returning the hot
air from the condenser to the fire-place, and what you think the
effect will be.
"The Comptroller of the Navy has not yet returned from Plymouth,
therefore no answer has been given to me.
"You will see by the sketch how very small and compact an engine is
now brought without complication or difficulty; each surface foot of
boiler and condenser is equal to one-third of a horse-power, weighing
20 lbs., or 60 lbs. weight for each horse-power. The consumption of
fuel is so small when working a differential engine, that I expect it
will not exceed 1 lb. of coal per hour for each horse-power.
"The cost of erection and required room are so small from its
simplicity that it will be generally used. As I am very anxious that
every possible improvement should be considered prior to making a
specification for a patent, I must beg that you will have the goodness
to consider and calculate on the data I have given you. I am sorry to
trouble you, but I am satisfied this will be to you rather a pleasing
amusement than a trouble. The warming machines will take a very
extensive run, and I believe will pay exceedingly well.
"I am almost in the mind to take a ride down to see you in a few days,
but am now detained here about the American mining concerns.
"I remain, Sir,
"Your very humble servant,
"RD. TREVITHICK."
The letters and foot-note are the only changes made by the writer
in Trevithick's original sketch so descriptive of a wonderful
application of varied and improved principles of long-known difficulty
and importance; the beautifully compact tubular boiler for giving
high-pressure superheated steam, surface condensation, absence of
feed and condensing water, and return of the heat, in other engines
wasted in condensation, to the fire-place; though there is little or
no mention of the mechanical or moving parts of the steam-engine, yet
its vital principles are grasped with the hand of a master. The sketch
in the letter hastily made forty years ago is more ingenious than any
portable engine since constructed, though there may be no sufficient
proof of its practical success. The propeller to be worked by this
novel engine was of course his long-idle screw.
_Steam Engines, 21st February, 1831._
"NOW KNOW YE, that in compliance with the said proviso, I,
the said Richard Trevithick, do declare that the essential points in
my improved steam-engine, for which I claim to be the first and true
inventor, are:--
"Firstly, the placing of the boiler within the condenser, in order to
obtain the additional security of the strength of the condenser to
prevent mischief in case the boiler should burst, and also by the same
arrangement to conveniently make the condenser, with a very extensive
surface, enabling me to condense the steam without injecting water
into it.
"Secondly, the enclosing of the condenser in an air or water
vessel, by which the intention of safety from explosion is further
provided for, and my engine really rendered what I denominate it, a
high-pressure safety engine.
"Thirdly, the condensing of the steam in the condenser by means of a
current of cold air or cold water forced against the outsides of the
condenser.
"Fourthly, the returning of the condensed steam from the condenser
back again into the boiler, to the end that sediment and concretion in
the boiler may be prevented; and,
"Fifthly, the blowing of the fire with the air after it has been
heated by condensing the steam.
"In forming my improved steam-engine I employ several or all of
these points according to convenience, in combination with the other
necessary parts of steam-engines in common use.
"These, my essential points, will admit of various modifications as
to form and proportions such as must be and are quite familiar to
every competent steam-engine manufacturer, and therefore it will be
sufficient for the perfect description of my improved steam-engine
that I explain some of the modes of forming and combining the
essential points of my invention with the other parts of steam-engines
in common use. In my most favourite form of engine in which I condense
by a current of cold air, the fire-place and flue, the boiler, the
condenser, and the air-vessel, are made of six concentric tubes,
standing in an upright position. The inner or first tube forms the
fire-place and flue, and at the same time the inner side of the
boiler. This tube is conical, having its small end upwards. The next
or second tube is cylindrical, about 6 inches larger in diameter
than the lower end of the first tube, and forms the outside of the
boiler, leaving a space all round of about 3 inches at the bottom, and
so much more at the top, as the flue is taper for holding water and
steam between the two tubes. The third tube is about 2 inches larger
in diameter than the second, in order to allow a space of about an
inch for powdered charcoal or some other slow conductor of heat. This
tube also constitutes the inner side of the air-vessel. The fourth
tube is about 2 inches larger than the third, and forms the inner
side of the condenser. The fifth tube, about 2 inches larger than the
fourth, forms the outside of the condenser; and the sixth tube, about
2 inches larger than the fifth, forms the outside of the air-vessel,
and at the same time the outside of the whole of the generating
and condensing apparatus, consisting of fire-place, flue, boiler,
condenser, and air-vessel. These tubes are made of wrought-iron plates
riveted together, and are all cylindrical, except the first, which
is conical, the bottom or fire end being the largest. The first or
inner tube is closed at bottom, but has an opening on one side near
the bottom, through which the fire-bars are introduced, and the ashes
and clinkers taken away. To this opening a neck-piece about 3 inches
long is riveted, having a flange to fit against the inside of the
second tube, when the two tubes are concentric, through, the side of
which second tube is an opening corresponding with that in the first
tube, and the flanch is screwed to the second tube so as to make one
opening through the sides of the two tubes. The second tube extends
downwards about 5 inches below the first tube, and has a flanch
turning inwards, to which a second round plate of iron is screwed,
forming the bottom of the boiler. The first tube has an external
flanch at the top, and the second tube an internal flanch, both of the
same height, and screwed to a cast-iron circular plate or cap-piece,
which extends wide enough around the boiler to form also the cover
for the air-vessel. This plate has a hole in the middle as large as
the flue. The sides of the condenser and air-vessel are formed of
four concentric tubes, each about 2 inches larger than the one within
it. The inner and outer of these tubes constitute the sides of the
air-vessel, and are each furnished with an external flanch at the
top by which they are screwed to the cap-piece. The two intermediate
tubes constituting the sides of the condenser are riveted together at
the top, leaving a space of about an inch between their upper ends
and the cap-piece, so as to allow of a free communication over them
between the outer and inner parts of the air-vessel. The inner tube of
the air-vessel extends downwards about an inch below the boiler, and
is closed by a flat plate screwed on to a flanch projecting inwards
from the tube; the two tubes of the condenser descend about 3 inches
lower than the boiler. The inner tube has an internal flanch, to which
a flat circular plate is screwed to close up the tube. The outer
tube of the condenser is of the same length with the inner, and is
provided with an external flanch about 3 inches broad. The outer tube
of the air-vessel has an external flanch 2 inches broad, and is just
long enough to come down upon the broad flanch of the condenser last
described, and these two flanches are together bolted upon a bottom
piece of cast iron, which is a dish of 4 inches deep, and equal in
diameter with the diameter of the outer tube, and having a flanch the
same breadth as the flanch of the outer tube, and the bottom piece is
secured to the air-vessel and outer tube of the condenser by bolts
going through all the three flanches. An opening is made through the
sides of all the four tubes of the condenser and air-vessel opposite
to and as wide as the fire-place opening through the sides of the
boiler. The upper part of both openings to be of the same height,
but the outer opening is made as low as the bottom of the boiler, in
order to allow room for a pipe to enter that part of the boiler for
forcing the water into it, and also another pipe and cock for drawing
off the water or sediment, in case foul water be used by accident or
carelessness. These two openings through the condenser and air-vessel,
and through the boiler, constitute one fire doorway through all the
six tubes for access to the fire-place; a ring is placed between the
two tubes of the condenser around the fire doorway, so as to cut off
all communication of the steam in the condenser with the air in the
doorway; another similar ring is placed between the condenser and the
outer tube to prevent the escape of air into the fire doorway, and
a half ring is placed in the lower part of the fire doorway between
the condenser and the inner tube of the air-vessel, to prevent ashes
from falling into the air-vessel, and yet allow a free passage for
the air from the inner part of the air-vessel into the upper part of
the fire doorway. These two rings and the half ring are secured in
their places by rivets passing through all of them and through the
tubes, and uniting all firmly together, the interstices being filled
with iron cement. A ring is also placed between the boiler and the
air-vessel around the fire doorway, against the outside of which ring
the charcoal powder is tightly rammed, and will hold the ring in its
place without the necessity of either rivets or screws. That part
of the fire doorway which is above the fire-bars is supplied with
an inner door, to shut the fire-place even with the outside of the
boiler, and exclude all access of air to the fire, except through the
grating. The whole of the fire doorway is enclosed by an outer door
even with the outside of the air-vessel, to exclude all air, except
that which comes through the air-vessel; a pipe is fixed in the bottom
or dish-piece leading to a forcing pump to draw the water out of the
condenser and force it into the bottom of the boiler through the pipe
before described. A blowing cylinder of about ten times the content of
the main cylinder is screwed against the outside of the air-vessel,
and opposite to the two outlet valves of the blowing cylinder two
apertures are made in the air-vessel, through which the air is
forced in. The main cylinder of the engine, of the usual dimensions
according to power wanted, is also screwed against the outside of the
air-vessel high enough above the blowing cylinder to allow room for
the main-crank shaft to work between them. The forcing pump before
mentioned is also screwed to the outside of the air-vessel, and thus
my improved steam-engine becomes more compact and convenient than any
preceding steam-engine. For the purpose of supplying the boiler with
distilled water, in case there should be a deficiency in it, a small
vessel made of two upright tubes, one within the other, is placed on
the cap-piece. The inner tube is of the same diameter as the flue, and
forms a continuation of it. The outer tube is about 6 inches larger
than the inner, and the space at the top and bottom between the two
tubes is closed by two ring-shaped pieces. This vessel may be about
18 inches high; a cock is fixed in the top of this vessel, to which
a bent pipe is fastened, leading to and united with a pipe which
arises from the top of the condenser and passes through a hole in the
cap-piece, and thus a communication between the supplying vessel and
the condenser may be opened or shut at pleasure; another pipe, also
furnished with a stop-cock, arises from the vessel, and communicates
with a water-cistern to receive its supply of water when required; a
third pipe, having a cock in it, opens into the vessel near the bottom
to let out the sediment; a small cock to let the air out is also fixed
in the top of the vessel, which cock may also be used for letting air
out of the condenser. In order to supply the boiler with water by
means of this vessel, the stop-cock leading to the condenser is shut,
and that leading to the cistern is opened, and at the same time the
air-cock is opened to allow the air to escape that the water may fill
the vessel. When the vessel is nearly full of water, the air-cock
and the cock from the cistern are shut, and that in the pipe leading
to the condenser is opened. The water being then heated by the flue
is converted into steam, which, passing into the condenser, is there
reduced to water again, leaving the sediment or salt in the supplying
vessel, which sediment or salt may be occasionally blown out through
the bottom pipe by filling the vessel with, water, shutting the water,
steam, and air cocks, and opening the cock of the outlet pipe at a
time when the steam in the vessel is strong. But the supply of water
from the condenser being always equal to that converted into steam
and used in the engine, there is no tendency to a variation in the
height of the water in the boiler, except there be leakage or waste
of steam in some part of the engine. An upright glass tube, having
an iron tube of communication with the lower part of the boiler and
another iron tube of communication to the upper part of the boiler, is
conveniently placed against the outside of the air-vessel to indicate
at all times the height of the water in the boiler; as is usual in
steam-boilers, a valve is placed on the top of the air-vessel to
allow of the escape of a portion of the air in case that the quality
of the fuel should not require so much air for perfect combustion
as the steam requires for good condensation. The degree of the
condensation of the steam may be increased at pleasure, by increasing
the velocity of the air passing into and through the air-vessel. The
other parts of my improved steam-engine, such as the steam-pipes,
the throttle-valve, the safety-valve, the vacuum-valve, the working
valves, crank, connecting rods, cross-heads, pistons, piston-rods,
and various other minor parts common to engines in general use may be
made in the usual forms, and placed in the most convenient situations;
they cannot, therefore, need any description. When it is intended to
use water for condensing instead of air, my improved steam-engine must
be made as before directed, except that the communication between
the air-vessel and the fire-place must be closed, which may be done
by a perfect ring of iron surrounding the opening leading to the
fire-place, instead of the half ring before described, and a forcing
pump must be employed to draw water from a reservoir, and force it
into the vessel which I have hereinbefore denominated the air-vessel,
but which in this mode of working would more properly bear the name
of water-vessel. In this case a blowing cylinder, the dimensions of
which must be calculated according to the quality of the fuel to be
used, may be worked to blow the fire through a pipe leading into the
ash-pit. This, however, will not be necessary where there is a chimney
high enough to create a strong draught. In respect to proportions, my
improved steam-engine admits of considerable latitude, and it will
be sufficient direction to any practical engineer to say that for
engines working with steam of 120 lbs. to the inch, used expansively
till it be nearly reduced to atmospheric strength and then condensed,
a 10-horse engine may have a fire-place of 20 inches diameter, the
flue at the top 10 inches diameter, and a boiler of 20 feet high; a
60-horse engine, a fire-place of 36 inches diameter, a flue of 16
inches diameter, and a boiler of 20 feet high. In boat-engines, and
in other cases where height cannot be allowed, the diameter must be
increased. The thickness of the two tubes constituting the boiler
sides of a 10-horse engine may be 1/8th of an inch, that of a 60-horse
a quarter of an inch, and so in proportion for engines of other power.
The tubes constituting the condenser and inner tube of the air-vessel
may in all cases be 1/8th of an inch thick. The outer tube may be
3/8ths of an inch thick, to afford stability to the working cylinder,
the blowing cylinder, and the forcing pump fastened to this tube,
and as an ultimate perfect barrier against explosion. The respective
distances of the other tubes constituting the outside of the boiler,
the condenser, and air-vessel, will be the same as hereinbefore given,
and therefore their diameters will depend upon the diameter of the
fire-place. The cap-piece in small engines may be half an inch thick,
and in large engines an inch. The bottom of the ash-pit and bottom of
the boiler must have about half an inch of thickness for every foot
diameter, or they may be cast with ribs to afford equivalent strength.
The fuel is supplied through a door in the flue, at the top of the
boiler, consisting of coke or coals the least liable to swell with
heat. The flue may be filled to about one-third of the height of the
boiler, and the water fill about three-fourths of the boiler, leaving
one-fourth for steam.
"Having clearly explained my improved steam-engine so that any person
competent to make a steam-engine can from this description understand
my invention and carry the same into effect in as beneficial a manner
as myself, I proceed to observe that the extreme safety of my
improved steam-engine will be seen, from considering that in case the
boiler should explode inwards into the flue, the power of the steam
would be first reduced by filling the flue and fire-place, and could
not escape through the chimney and fire doorway faster than it would
diffuse itself and be condensed by mixing with the surrounding air,
and thus lose all its force. But should the outside of the boiler
burst, part of the force of the steam would be spent in filling up
the interstices between the particles of the charcoal, and would then
probably be too weak to effect a breach through the inner tube of the
air-vessel; and should such a second breach be effected, the space
within the air-vessel would allow the steam to expand and partly
condense, and a portion to escape into and through the fire doorway,
where it would divide itself, and proceed harmlessly up the flue,
and out at the doorway; so that the outer case being a reserve of
strength, would to a certainty withstand the force remaining in the
steam after the before-mentioned successive reductions of power."
The patent of February, 1831, perfects the sketch in his letter of
July 27th, 1829, which in its turn made more perfect the plans put
into practice in 1815, just before leaving England for America.[175] The
prejudice against the use of his high-pressure steam-engine he tried
to meet by calling it "a high-pressure safety engine." The boiler was
of six wrought-iron upright tubes, one within the other. The inner one
was the fire-tube, surrounded by a tube of larger diameter, forming
the water and steam space. This was again surrounded by another tube,
2 inches larger in diameter, the space being filled with charcoal or
other non-conductor of heat; another tube, 2 inches more in diameter,
formed the inner circle of the condenser, having an inch space for
the passage of cold air from the blowing cylinder, carrying the heat
from the condensing steam back to the fire-place. Still another tube,
2 inches more in diameter, giving a space into which the used steam
from the cylinder passed to be condensed. Then came the outside tube,
2 inches more in diameter, forming a second space for the passage of
air, taking heat from the condenser into the fire. The steam-boiler had
its heat retained by a coating of charcoal; next to it came a current
of cold air an inch thick, carrying back to the fire any heat that had
passed through the charcoal coat, and also the heat from the inner
surface of the condenser. Then came the inch-thick circle of steam, on
its exit from the cylinder, to be condensed; and finally an outside
circle of cold air, performing the same functions as the inner circle
in condensing the steam and carrying its heat back again to the fire.
[Footnote 175: See Trevithick's letters, July 8th, 1815, vol. ii., p. 80,
and 7th, vol. i., p. 364; and 16th May, vol. i., p. 370; and patent of
1815, vol. i., p. 375.]
The object or principle of this engine was to avoid the loss of
heat, and the necessity for either condensing water or feed-water,
as described in the letter and drawing of August 19th, 1830, but the
detail was changed, mainly to facilitate construction. As in practice
it might be impossible to fully attain those objects, preparation was
made to get rid of the salt from such water as might be required as
feed-water to make good the loss from leakage or other defects in the
working of marine steam-engines. The specification states: "For the
purpose of supplying the boiler with distilled water, in case there
should be a deficiency in it, a small vessel made of two upright tubes,
one within the other, is placed on the cap-piece. The inner tube is
of the same diameter as the flue, and forms a continuation of it. The
water being heated by the flue is converted into steam, which, passing
into the condenser, is there reduced to water again, leaving the
sediment or salt in the supplying vessel."
Where water condensation was preferred the surface-air condenser could
be converted into a surface-water condenser by a current of cold water
in place of the air; in which case the air from the blowing cylinder
was taken direct in to the fire-place or other means used for giving
the necessary draught. Steam of about 135 lbs. to the inch was to be so
expansively worked as at the finish of the stroke, on its escape to the
condenser, to be no more than atmospheric pressure, or 15 lbs. to the
inch--just the strength with which Watt preferred to commence his work
in the cylinder.
The most prominent feature in Trevithick's numerous modifications of
the steam-engine was the boiler. In the 'Life of Watt,' though his
commentators have been numerous and eminent, little or nothing is said
about the boiler or the steam pressure. He left that all-important
part of the steam-engine just as he found it, resisting the increase
of steam pressure, which was the mainspring of Trevithick's engine.
The boiler of the high-pressure engines of 1796[176] sheltered the
steam-cylinder from cold; and the used steam from the cylinder
circulated around the exterior of the boiler, on its way to the
blast-pipe, while the condensed portion was returned as feed-water
in the patent engine of 1802.[177] In 1811 he proposed to force air
into the fire-place, hoping thereby to reduce the amount of heat lost
by the chimney.[178] His various forms of tubular boilers, as at the
Herland Mine,[179] and at Dolcoath,[180] and the upright multitubular
boilers patented in 1815.[181] followed up in 1828. "I shall have a small
portable engine finished here next week, and will try to heat steam
independent of water, in small tubes of iron, on its passage from the
boiler to the cylinder, and also try cold sides for condensing." In
1829 a simple boiler and condenser composed of three tubes was made,
the inner or fire-tube being 2 feet in diameter and 15 feet long, "for
the express purpose of experimenting on the working the same steam and
water over and over again;"[182] and on the same subject, "By making the
condenser of 4-inch copper tubes 1/32nd of an inch thick, it would
stand in one-twentieth part of the space of the boiler:"[183] and finally
the sketch of the tubular boiler and tubular condenser of 1830, in its
boiler portion similar to the best portable boilers of the present day,
and the patent specification of 1831. Surely therefore to him belongs
the credit of having invented and perfected the tubular boiler and
surface condenser.
[Footnote 176: See vol. i., p. 104.]
[Footnote 177: See patent specification, vol. i., p. 128.]
[Footnote 178: See Trevithick's letter, 13th Jan., 1811, vol. ii., p. 6.]
[Footnote 179: See vol. ii., p. 71.]
[Footnote 180: See chap. xx.]
[Footnote 181: See Trevithick's letters, 8th July, 1815, vol. ii., p. 80;
and 7th and 16th May, vol. i., pp. 364, 370.]
[Footnote 182: See vol. ii., p. 332.]
[Footnote 183: See vol. ii., p. 336.]
Smiles has written:[184]--
[Footnote 184: See 'Life of George Stephenson,' by Smiles, p. 279;
published 1857.]
"For many years previous to this period (1829), ingenious mechanics
had been engaged in attempting to solve the problem of the best and
most economical boiler for the production of high-pressure steam.
Various improvements had been suggested and made in the Trevithick
boiler, as it was called, from the supposition that Mr. Trevithick
was its inventor. But Mr. Oliver Evans, of Pennsylvania, many years
before employed the same kind of boiler, and as he did not claim the
invention, the probability is that it was in use before his time. The
boiler in question was provided with an internal flue, through which
the heated air and flames passed, after traversing the length of the
under side of the boiler, before entering the chimney.
"This was the form of boiler adopted by Mr. Stephenson in his
Killingworth engine, to which he added the steam-blast with such
effect. We cannot do better than here quote the words of Mr. Robert
Stephenson on the construction of the 'Rocket' engine:--'After the
opening of the Stockton and Darlington, and before that of the
Liverpool and Manchester Railway, my father directed his attention to
various methods of increasing the evaporative power of the boiler of
the locomotive engine. Amongst other attempts, he introduced tubes
(as had before been done in other engines)--small tubes containing
water, by which the heating surface was materially increased. Two
engines with such tubes were constructed for the St. Etienne Railway,
in France, which was in progress of construction in the year 1828;
but the expedient was not successful; the tubes became furred with
deposit, and burned out.
"'Other engines, with boilers of a variety of construction, were
made, all having in view the increase of the heating surface, as it
then became obvious to my father that the speed of the engine could
not be increased without increasing the evaporative power of the
boiler. Increase of surface was in some cases obtained by inserting
two tubes, each containing a separate fire, into the boiler; in
other cases the same result was obtained by returning the same tube
through the boiler; but it was not until he was engaged in making
some experiments, during the progress of the Liverpool and Manchester
Railway, in conjunction with Mr. Henry Booth, the well-known
secretary of the company, that any decided movement in this direction
was effected, and that the present multitubular boiler assumed a
practicable shape. It was in conjunction with Mr. Booth that my father
constructed the 'Rocket' engine.
"'In this instance, as in every other important step in science or
art, various claimants have arisen for the merit of having suggested
the multitubular boiler as a means of obtaining the necessary heating
surface. Whatever may be the value of their respective claims, the
public, useful, and extensive application of the invention must
certainly date from the experiments made at Rainhill. M. Seguin, for
whom engines had been made by my father some few years previously,
states that he patented a similar multitubular boiler in France
several years before. A still prior claim is made by Mr. Stevens, of
New York, who was all but a rival to Mr. Fulton in the introduction of
steamboats on the American rivers. It is stated that as early as 1807
he used the multitubular boiler.
"'These claimants may all be entitled to great and independent merit;
but certain it is, that the perfect establishment of the success of
the multitubular boiler is more immediately due to the suggestion of
Mr. Henry Booth, and to my father's practical knowledge in carrying it
out.'
"We may here briefly state that the boiler of the 'Rocket' was
cylindrical, with flat ends, 6 feet in length, and 3 feet 4 inches in
diameter. The upper half of the boiler was used as a reservoir for
the steam, the lower half being filled with water. Through the lower
part twenty-five copper tubes of 3 inches diameter extended, which
were open to the fire-box at one end and to the chimney at the other.
The fire-box, or furnace, 2 feet wide and 3 feet high, was attached
immediately behind the boiler, and was also surrounded with water."
Stephenson knew of Trevithick's patent of 1802,[185] in which a
three-tubed boiler is shown; and it was after that time that Oliver
Evans and Fulton tried their experiments, and also the numerous engines
with single or return double tube, at work in the principal towns of
England prior to 1804,[186] and near his residence in childhood and in
manhood.[187]
[Footnote 185: See vol. i., p. 128.]
[Footnote 186: See Trevithick's letter, Sept. 23rd, 1804, vol. ii., p. 2.]
[Footnote 187: Mr. Armstrong's note, vol. i., p. 184.]
George Stephenson's Killingworth boiler, "to which he added the
steam-blast with such effect," was a copy of Trevithick's boiler and
blast, working since 1804 in Newcastle-on-Tyne, and was precisely the
boiler described by Stephenson; "in other cases the same result was
obtained by returning the same tube through the boiler." This is an
admission from Stephenson that Trevithick's patent boiler was the best
in use up to about 1828.
A further proof of the indirect public gain from the use of
Trevithick's return-tube boiler over a period of thirty years is their
having supplied high-pressure expansive steam in the first experiments
made with such steam by the Admiralty, at whose request Mr. Rennie
and others examined the duty of the Cornish high-pressure expansive
engine, and Captain King, R.N., in charge of the Admiralty Department
at Falmouth in 1830, gave an order to Harvey and Co. to construct
high-pressure steam-boilers for the Government vessel 'Echo'; in 1831
the machinery was put on board the 'Echo' in the Government Dockyard
at Plymouth, and included three of Trevithick's return-tube boilers,
made of wrought iron, each 5 feet 6 inches in diameter and 24 feet
long, with internal return fire-tube 2 feet 2 inches in diameter. The
fire-place end of the boiler was 6 feet 9 inches deep by 5 feet 6
inches wide, to give room for the fire-place and ash-pit. The steam
pressure was 20 lbs. on the inch above the atmosphere, worked by
double-beat valves, 6 inches in diameter, with expansive gear.
This new machinery was fixed under the superintendence of the writer,
after which the Government engineers took charge of the vessel, and
the writer who had, as the mechanic in charge, worked like a slave,
though receiving but 1_s._ 6_d._ a day and expenses, was not invited to
take any part in the experimental trials, nor ever heard of the result
except in the ordinary rumours of Admiralty bungling on board the
'Echo.'
Those boilers were similar to the Trevithick boiler that had served
the locomotive in Newcastle and elsewhere from 1801 to 1828, the first
steamboat experiments in England, in Scotland, and in America, and the
numerous high-pressure engines then at work.
[Illustration: BOTTLE-NECK BOILER.]
The enlarging the fire-place end of boilers or fire-tubes has led
to many forms. Trevithick's model of 1796[188] had an oval tube
giving a greater spread of fire-*bars; the same is seen in the 1808
steamboat;[189] the Dolcoath boilers of 1811[190] show the oval and also
the bottle-neck fire-tube; the Welsh locomotive of 1804[191] had the
fire-tube contracted at its bend or return portion; the Tredegar
puddling-mill fire-tube of 1801[192] tapered gradually from the
fire-bridge to the chimney end; in the London locomotive of 1808[193]
the fire-tube took the bottle-neck shape close to the fire-bridge. The
accompanying sketch shows the bottle-neck contraction, only on the
top and sides of the fire-tube was to give breadth to the fire-bars
_d_, and thickness to the fire at bridge _c_, after which the flue
portion of the fire-tube was contracted: this boiler was for many
years a favourite in Cornwall. The bottle-neck contraction of the
'Echo' boiler was similar to the above, except that the enlargement of
the fire-place was downwards instead of upwards, and the fire-tube,
instead of going through the end of the boiler, returned to near the
enlarged fire-place, when it passed out through the side of the boiler
to the chimney, just as in the Tredegar puddling-mill boiler; all those
variations were with the object of increasing the fire-grate, and at
the same time keeping down the gross size and weight of boiler and its
water.
[Footnote 188: See vol. i., p. 104.]
[Footnote 189: See vol. i., p. 335.]
[Footnote 190: See vol. ii., p. 169.]
[Footnote 191: See vol. i., p. 181.]
[Footnote 192: See vol. i., p. 223.]
[Footnote 193: See vol. i., p. 207.]
In 1805, Lord Melville failed to keep his appointment with Trevithick,
on his proposal to construct a high-pressure steamboat.[194] Rennie, a
pupil and friend of Watt, and familiar with Trevithick's high-pressure
steam-dredgers on the Thames, was employed by Lord Melville and the
Admiralty on the Plymouth Breakwater, where in 1813 Trevithick proposed
the use of his high-pressure steam locomotive and boring engine.[195]
In 1820 Rennie wrote to Watt, that the Admiralty had at last decided
upon having a steamer; at that time fifteen years had passed since
Trevithick's offer to propel the Admiralty by steam-puffers, and ten
years more were to pass before they could make up their minds to
venture on high-pressure steam from his boilers. The Steam Users'
Association are equally hesitating, judging from words just spoken by
an engineer, the son of an engineer:--
[Footnote 194: See Trevithick's letter, 10th Jan., 1805, vol. i., p. 324.]
[Footnote 195: Ibid., vol. ii., p. 24.]
"Sir William Fairbairn said he had come to the conclusion, after
many years' experience, that it was in their power to economize the
present expenditure of fuel by a system which might not be altogether
in accordance with the views of the members of the association or
the public at large, and that was to increase the pressure of steam.
He would have great pleasure in stating a few facts which might some
day tend to bring about a change, if not a new era, in the use of
steam. From the result of a series of experimental researches in which
he had been engaged for several years on the density, force, and
temperature of steam, he had become convinced that in case we were
ever to attain a large economy of fuel in the use of steam, it must
be at greatly-increased pressure, and at a rate of expansion greatly
enlarged from what it was at present. Already steam users had effected
a saving of one-half the coal consumed by raising the pressure from
7 lbs. and 10 lbs.--the pressure at which engines were worked forty
years ago--to 50 lbs., or in some cases as high as 70 lbs. on the
square inch."[196]
[Footnote 196: 'The Engineer,' March 15th, 1872: remarks by the Chairman
at a meeting of the Manchester Steam Users' Association.]
Dear me! would have been Trevithick's exclamation had he read this;
did I devote my whole life to the making known the advantages of
high-pressure steam, and did I, seventy years ago,[197] really work
expansive steam of 145 lbs. on the inch in the presence of many of the
leading engineers of the day! Of course this short extract of a speech
made by a member of a practical society, may not be taken as conveying
fully the speaker's views, but it illustrates the immense difficulty
Trevithick encountered in making his numerous plans acceptable to the
public.
[Footnote 197: See Trevithick's letter, August 20th, 1802, vol. i., p.
154.]
Another modern statement bearing on inventions originating with
Trevithick, but wearing new garbs with new names, shows the same
tendency to ignore old friends, or, to say the least of it, to pass
them by:--
"The trial of No. 36 steam-pinnace was made at Portsmouth yesterday.
Her peculiarity consists in the arrangement of her propelling
machinery, in the adaptation of the outside surface condenser, and
a vertical boiler, both patented by Mr. Alexander Crichton. The
condenser is simply a copper pipe passing out from the boat on one
quarter at the garboard strake, and along the side of the keel,
returning along the keel on the opposite side, and re-entering the
boat on that quarter. The boiler is designed for boats fitted with
condensing engines, and which, therefore, are without the acceleration
of draught given by the exhausted steam being discharged into the
funnel. It is of the vertical kind, and stands on a shallow square
tank, which forms the hot well. The tubes are horizontal over
the fire, the water circulating through them. The condensed steam
is pumped into the well at a temperature of 100°, and being there
subjected to the heat radiating from the furnace, is pumped back into
the boilers at nearly boiling point. It is estimated that, under these
conditions, the pinnace would run for nearly 48 hours without having
to 'blow off' or carry a supply of fresh water, the waste water being
made good by sea water."[198]
[Footnote 198: 'The Times,' November 24th, 1871.]
The peculiarity of this steam-pinnace of 1871, on which a patent was
granted, is stated to be a metal surface condenser exposed to the cold
water at the bottom of the boat, returning the condensed steam at
about boiling temperature to the boiler, and a vertical boiler with
horizontal tubes through which the water circulates, both of which
in principle, if not in detail, are seen in the surface condenser of
Trevithick's iron-bottom ship of 1809, and his vertical boiler of
1816,[199] and further illustrated in the inventions spoken of in this
and the following chapter; and yet on so all-important a subject, dealt
with in various ways by Trevithick from 1804 to 1832, his plans are
reproduced as discoveries in 1871.
[Footnote 199: See vol. i., pp. 336, 364, 370.]
About 1828, Mr. Rennie, Mr. Henwood, and others, reported on the
advantages of high-pressure expansive steam in Wheal Towan engine,[200]
on the north cliffs of Cornwall, near Wheal Seal-hole Mine on St. Agnes
Head, where in 1797 Trevithick had worked his first high-pressure
steam-puffer engine in competition with the Watt low-pressure
steam-vacuum engine. Captain Andrew Vivian was then his companion, and
the Cow and Calf, two rocks of unequal size, a mile from the land, were
from that time called Captain Dick and Captain Andrew, or the Man and
his Man, and there they still remain in the Atlantic waves, fit emblems
of their namesakes and their still living inventions. The stir made by
those expansive trials led to the experiment in the 'Echo,' of which
Mr. Henwood[201] thus speaks:--
[Footnote 200: See Mr. Henwood's report, vol. ii., p. 185.]
[Footnote 201: Residing at Penzance, 1871.]
"Captain William King, R.N., Superintendent of the Packet Station
at Falmouth, attempted to impress on Viscount Melville, then First
Lord of the Admiralty, the advantage of using high-pressure steam
expansively in the Royal Navy, to whom Lord Melville replied that
he had been taught by his friend, the late Mr. Rennie, that the
danger attending such a course was very great, and that it would be
difficult, if not impossible, to persuade him to the contrary."
[Illustration: CAPTAIN DICK AND CAPTAIN ANDREW, OR THE MAN AND HIS
MAN. [W. J. Welch.]]
Twenty-five years of precept and example caused the Admiralty to follow
suit, and to request Mr. Ward, a Cornish engineer, to construct boilers
and expansive valves for the Government steamboat 'Echo.' The writer
was entrusted with fixing the machinery in the vessel at the Plymouth
Dockyard, and before starting with it from Harvey and Co.'s foundry,
waited on Captain King, R.N., at Falmouth, for his instructions, in
happy ignorance of the fear of the Lords of the Admiralty to tread on
Cornish high-pressure. After eying the applicant as captains in Her
Majesty's service are apt to do when dealing with boys in the civil
service, he vouchsafed to say, "Mind, young man, what you are about,
for if there is a blow up, by ---- you'll swing at the yard-arm."