Various - Scientific American Supplement, No. 312, December 24, 1881

V >> Various >> Scientific American Supplement, No. 312, December 24, 1881

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It has been found, on the whole, more convenient to expand the steam
in two or more cylinders, rather than in one. I quite agree that, as a
mere matter of engineering science, there is no reason why the
expansion should not take place in a single cylinder, unless it be
that a single cylinder is cooled down to an extent which cannot be
overcome by jacketing, and which, therefore, destroys a portion of the
steam on its entering into the cylinder.

As regards the propeller, as we know, except in certain cases, the
paddle-wheel has practically disappeared, and the screw propeller is
all but universally employed. The substitution of the screw propeller
for the paddle enables the engine to work at a much higher number of
revolutions per minute, and thus a very great piston speed, some 600
ft. to 800 ft. per minute, is attained; and this, coupled with the
fairly high mean pressure which prevails, enables a large power to be
got from a comparatively small-sized engine. Speeds of 15 knots an
hour are now in many cases maintained, and on trial trips are not
uncommonly exceeded. Steam vessels are now the accepted vessels of
war. We have them in an armored state and in an unarmored state, but
when unarmored rendered so formidable, by the command which their
speed gives them of choosing their distance, as to make them, when
furnished with powerful guns, dangerous opponents even to the best
armored vessels.

MARINE GOVERNORS.

We have also now marine engines, governed by governors of such extreme
sensitiveness as to give them the semblance of being endowed with the
spirit of prophecy, as they appear rather to be regulating the engine
for that which is about to take place than for that which is taking
place. This may sound a somewhat extravagant statement, but it is so
nearly the truth, that I have hardly gone outside of it in using the
words I have employed. For a marine governor to be of any use, it must
not wait till the stern of the vessel is out of the water before it
acts to check the engine and reduce the speed. Nothing but the most
sensitive, and, indeed, anticipatory action of the governors can
efficiently control marine propulsion. Instances are on record of
vessels having engines without marine governors being detained by
stress of weather at the mouth of the Thames, while vessels having
such governors, of good design, have gone to Newcastle, have come
back, and have found the other vessels still waiting for more
favorable weather.

With respect to condensation in marine engines, it is almost
invariably effected by surface condensers, and thus it is that the
boilers, instead of being fed with salt water as they used to be,
involving continuous blowing off, and frequently the salting up, of
the boiler, are now fed with distilled water. It should be noticed,
however, that in some instances, owing to the absence of a thin
protecting scale upon the tubes and plates, very considerable
corrosion has taken place when distilled water, derived from
condensers having untinned brass tubes, has been used, and where the
water has carried into the boiler fatty acids, arising from the
decomposition of the grease used in the engine; but means are now
employed by which these effects are counteracted.

LIGHT ENGINES AND BOILERS.

I wish, before quitting this section of my subject, to call your
attention to two very interesting but very different kinds of marine
engines. One is the high-speed torpedo vessel, or steam launch, of
which Messrs. Thornycroft's firm have furnished so many examples. In
these, owing to the rate at which the piston runs to the initial
pressure of 120 lb. and to very great skill in the design, Messrs.
Thornycroft have succeeded in obtaining a gross indicated horse-power
for as small a weight as half a cwt., including the boiler, the water
in the boiler, the engine, the propeller shaft, and the propeller
itself.

To obtain the needed steam from the small and light boiler, recourse
has to be made to the aid of a fan blast driven into the stoke-hole.
From the use of a blast in this way advantages accrue. One is, as
already stated, that from a small boiler a large amount of steam is
produced. Another is that the stoke-hole is kept cool; and the third
is that artificial blasts thus applied are unaccompanied by the
dangers which arise, when under ordinary circumstances the blast is
supplied only to the ash-pit itself.

THE PERKINS SYSTEM.

The second marine engine to which I wish to call your attention is one
that has been made with a view to great economy. The principles
followed in its construction are among those suggested by the
President (Sir W.G. Armstrong) in his address. He (you will remember)
pointed out that the direction in which economy in the steam engine
was to be looked for was that of increasing the initial pressure;
although at the same time he said that there were drawbacks in the
shape of greater loss, by radiation, and by the higher temperature at
which the products of combustion will escape. We must admit the fact
of the latter source of loss, when using very high steam, it being
inevitable that temperature of the products of combustion escaping
from a boiler under these conditions must be higher than those which
need be allowed to escape when lower steam is employed; although I
regret to say that in practice in marine boilers working at
comparatively low pressures the products are ordinarily suffered to
pass into the funnel at above the temperature of melted lead. But with
respect to the loss by radiation in the particular engine I am about
to mention--that of Perkins--there is not as much loss as that which
prevails in the ordinary marine boilers, because the Perkins boiler is
completely inclosed, with the result that while there is within the
case a boiler containing steam of 400 lb. on the square inch, and the
fire to generate that steam, the hand may be applied to the casting
itself, which contains the whole of the boiler, without receiving any
unpleasant sensation of warmth. By Mr. Perkins's arrangement, using
steam of 400 lb. in the boiler, it was found, as the result of very
severe trials, conducted by Mr. Rich, of Messrs. Easton and Anderson's
firm, and myself--trials which lasted for twelve hours--that the total
consumption of fuel, including that for getting up steam from cold
water, was just under 1.8, actually 1.79 lb. per gross indicated
horse-power per hour. That gross indicated horse-power was obtained in
a manner which it is desirable should always be employed in steamboat
trials. It was not got by using as a divisor the horse-power of the
most favorable diagram obtained during the day; but it was got from
diagrams taken during the regular work; then, every half-hour, when
the pressure began to die down, from coal being no longer put upon the
fire, diagrams taken every quarter of an hour, and then toward the
last, every five minutes; and the total number of foot pounds were
calculated from these diagrams, and were used to obtain the gross
indicated horse-power.

Further, so far as could be ascertained by the process of commencing a
trial with a known fire, and closing that trial at the end of six
hours, with the fire as nearly as possible in the same condition, the
consumption was 1.66 lb. of coal per gross indicated horse-power per
hour. So that, without taking into account the coal consumed in
raising steam from cold water, the engine worked for 1-2/3 lb. of coal
per horse per hour. I think it well to give these details, because
undoubtedly it is an extremely economical result.

ETHER ENGINE.

Our president alluded to the employment of ether as a means of
utilizing the heat which escaped into the condenser, and gave some
account of what was done by Mons. Du Tremblay in this direction. It so
happened that I had occasion to investigate the matter at the time of
Du Tremblay's experiments; very little was effected here in England,
one difficulty being the excise interference with the manufacture of
ether. Chloroform was used here, and it was also suggested to employ
bisulphide of carbon. In France, however, a great deal was done. Four
large vessels were fitted with the ether engines, and I went over to
Marseilles to see them at work. I took diagrams from these engines,
and there is no doubt that, by this system, the exhaust steam from the
steam cylinder, which was condensed by the application of ether to the
surface of the steam condenser (producing a respectable vacuum of
about 22 inches), gave an ether pressure of 15 lb. on the square inch
above atmosphere, and very economical results as regards fuel were
obtained. The scheme was, however, abandoned from practical
difficulties. It need hardly be said that ether vapor is very
difficult to deal with, and although ether is light, the vapor is
extremely heavy, and if there is any leakage, it goes down into the
bilges by gravitation, and being mixed with air, unless due care is
taken to prevent access to the flues, there would be a constant risk
of a violent explosion. In fact, it was necessary to treat the engine
room in the way in which a fiery colliery would be treated. The
lighting, for instance, was by lamps external to the engine room, and
shining through thick plate-glass. The hand lamps were Davy's. The
ether engine was a bold experiment in applied science, and one that
entitles Du Tremblay's name to be preserved, and to be mentioned as it
was by our president.

THE QUICKSILVER ENGINE.

These was another kind of marine engine that I think should not be
passed over without notice; I allude to Howard's quicksilver engine.
The experiments with this engine were persevered in for some
considerable time, and it was actually used for practical purposes in
propelling a passenger steam-vessel called the Vesta, and running
between London and Ramsgate. In that engine the boiler had a double
bottom, containing an amalgam of quicksilver and lead. This amalgam
served as a reservoir of heat, which it took up from the fire below
the double-bottom, and gave forth at intervals to the water above it.
There was no water in the boiler, in the ordinary sense of the term,
but when steam was wanted to start the engine, a small quantity of
water was injected by means of a hand-pump, and after the engine was
started, there was pumped by it into the boiler, at each half
revolution, as much water as would make the steam needed. This water
was flashed on the top surface of the reservoir in which the amalgam
was confined, and was entirely turned into steam, the object of the
engineers in charge being to send in so much water as would just
generate the steam, but so as not to leave any water in the boiler.
The engines of the Vesta were made by Mr. Penn, for Mr. Howard, of
the King and Queen Ironworks, Rotherhithe. Mr. Howard was, I fear, a
considerable loser by his meritorious efforts to improve the
steam-engine.

There was used, with this engine, an almost unknown mode of obtaining
fresh water for the boiler. Fresh water, it will be seen was a
necessity in this mode of evaporation. The presence of salt, or of any
other impurity, when the whole of the water was flashed into steam,
must have caused a deposit on the top of the amalgam chamber at each
operation. Fresh water, therefore, was needed; the problem arose how
to get it; and that problem was solved, not by the use of surface
condensation, but by the employment of reinjection, that is to say,
the water delivered from the hot well was passed into pipes external
to the vessel; after traversing them, it came back into the injection
tank sufficiently cooled to be used again. The boilers were worked by
coke fires, urged by a fan blast in their ashpits, but I am not aware
that this mode of firing was a needful part of the system.

LOCOMOTIVE ENGINES.

I come now to the engines used for railways. At the British
Association meeting of 1831, the Manchester and Liverpool Railway had
been opened only about a year. The Stockton and Darlington coal line,
it is true, had carried passengers by steam power as early as 1825,
but I think we may look upon the Manchester and Liverpool as being the
beginning of the passenger and mercantile railway system of the
present day. At that time the locomotives weighed from eight to ten
tons, and the speed was about 20 miles per hour, with a pressure of
from 40 to 50 lb. The rails were light; they were jointed in the
chairs, which were generally carried on stone blocks, thus affording
most excellent anvils for the battering to pieces of the ends of the
rails--that is to say, for the destruction of the very parts where
they were most vulnerable. The engines were not competent to draw
heavy trains, and it was a common practice to have at the foot of an
incline a shed containing a "bank engine," which ran out after the
trains as they passed, and pushed them up to the top of the hill.
Injectors were then unknown, and donkey-pumps were unknown, and
therefore, when it was necessary to fill up the boiler, if it had not
been properly pumped up before the locomotive came to rest, it had to
run about the line in order to work its feed-pumps. To get over this
difficulty, it was occasionally the practice to insert into a line of
rails, in a siding, a pair of wheels, with their tops level with that
of the rails so that the engine wheels could run upon the rims. Then,
the locomotive being fixed to prevent it from moving off the pair of
wheels thus endways, it was put into revolution, its driving wheels
bearing, as already stated, upon the rims of the pair of wheels in the
rails, and thus the engine worked its feed-pumps without interfering
(by its needless running up and down the line) with the traffic. It
should have been stated, that at this time there was no link motion,
no practical expansion of the steam, and that even the reversal of the
engine had to be effected by working the sides by hand gear, in the
manner in use in marine engines. When the British Association
originated, although the Manchester and Liverpool Railway had been
opened for a year, there is no doubt that the 300 members who then
came to this city found their way here by the slow process of the
stage-coach, the loss of which we so much deplore in the summer and in
fine weather, but the obligatory use of which we should so much regret
in the miserable weather now prevailing in these islands.

In 1881, we know that railways are everywhere inserted. Steel rails,
double the weight of the original iron ones, are used. Wooden sleepers
have replaced the stone blocks, and they, in their turn, will probably
give way to sleepers of steel. The joints are now made by means of
fish-plates, and the most vulnerable part of the rail, the end, is no
longer laid on an anvil for a purpose of being smashed to pieces, but
the ends of the rails are now almost always over a void, and thereby
are not more affected by wear than is any other part of the rail. The
speed is now from 50 to 60 miles an hour for passenger trains, while
slow speed goods engines, weighing 45 tons, draw behind them coal
trains of 800 tons. The injector is now commonly employed, and, by its
aid, a careful driver of the engine of a stopping train can fill up
his boiler while at rest at the stations. The link motion is in common
use, to which, no doubt, is owing the very considerable economy with
which the locomotive engine now works.

As regards the question of safety, it is a fact that, notwithstanding
the increased speed, railway accidents are fewer than they were at the
slow speed. It is also a fact, that if the whole population of London
were to take a railway journey, there would be but one death arising
out of it. Four millions of journeys for one death of a passenger from
causes beyond his own control is, I believe, a state of security which
rarely prevails elsewhere. As an instance, the street accidents in
London alone cause between 200 and 300 deaths per annum. This safety
in railway traveling is no doubt largely due to the block system,
rendered possible by the electric telegraph; and also to the efficient
interlocking of points and signals, which render it impossible now for
a signal man to give an unsafe signal. He may give a wrong one, in the
sense of inviting the wrong train to come in; but, although wrong in
this sense, it would still be safe for that train to do so. If he can
give a signal, that signal never invites to danger; before he can give
it, every one of the signals, which ought to be "at danger," must be
"at danger," and every "point" must have been previously set, so as to
make the road right; then, again, we have the facing point-lock, which
is a great source of safety.

BRAKES.

Further, we have continuous brakes of various kinds, competent in
practice to absorb three miles of speed in every second of time; that
is to say, if a train were going 60 miles an hour, it can be pulled up
in 20 seconds; or, if at the rate of 30 miles, in 10 seconds. With a
train running at 50 miles an hour, it can be pulled up in from 15 to
20 seconds, and in a distance of from 180 to 240 yards. Moreover, in
the event of the train separating into two or more sections, the
brakes are automatically applied to each section, thereby bringing
them to rest in a short time. Another cause of safety is undoubtedly
the use of weldless tires. I was fortunate enough to attend the
British Association meeting many years ago at Birmingham, and I then
read a paper upon weldless tires, in which I ventured to prophesy
that, in ten years' time, there would not be a welded tire made; that
is one of the few prophecies that, being made before the event, have
been fulfilled. I may perhaps be permitted to mention, that at the
same time I laid before the section plans and suggestions for the
making of the cylindrical parts of boilers equally without seam, or
even welding. This is rarely done at the present time, but I am sure
that, in twenty years' time, such a thing as a longitudinal seam of
rivets in a boiler will be unknown. There is no reason why the
successive rings of boiler shells should not be made weldless, as
tires are now made weldless.

MOTORS.

The next subject I intend to deal with is that of motors. In 1831, we
had the steam-engine, the water-wheel, the windmill, horse-power,
manual power, and Stirling's hot air engines. Gas engines, indeed,
were proposed in 1824, but were not brought to the really practical
stage. We had then tide mills; indeed, we have had them until quite
lately, and it may be that some still exist; they were sources of
economy in our fuel, and their abandonment is to me a matter of
regret. I remember tide mills on the coast between Brighton and
Newhaven, another between Greenwich and Woolwich, another at
Northfleet, and in many other places. Indeed, such mills were used
pretty extensively; they were generally erected at the mouth of a
stream, and in that way the river bed made the reservoir, and even
when they were erected in other situations, those were of a kind
suitable for the purpose, that is, lowlying lands were selected, and
were embanked to form reservoirs. In 1881, windmills and water-wheels
are much the same, but the turbines are greatly improved, and by means
of turbines we are enabled to make available the pressure derived from
heads of water which formerly could not be used at all, or if used,
involved the erection of enormous water-wheels, such as those at
Glasgow and in the Isle of Man, wheels of some eighty feet in
diameter. But now, by means of a small turbine, an excellent effect is
produced from high heads of water. The same effect is obtained from
the water-engines which our president has employed with such great
success. In addition to these motors, we have the gas-engine, which,
within the last few years only, has become a really useful working and
economical machine. With respect to horse-power motors, we have not
only the old horse engines, but we have a new application, as it seems
to me, of the work of the horse as a motor. I allude to those cases
where the horse drawing a reaping or thrashing machine, not only pulls
it forward as he might pull a cart, but causes its machinery to
revolve, so as to perform the desired kind of work. This species of
horse-engine, though known, was but little used in 1831. With respect
to hot-air engines there have been many attempts to improve them, and
some hot-air engines are working, and are working with considerable
success; but the amount of power they develop in relation to their
size is small, and I am inclined to doubt whether it can be much
increased.

TRANSMISSION OF POWER.

I now come to the subject of the transmission of power. I do not mean
transmission in the ordinary sense by means of shafting, gearing, or
belting, but I mean transmission over long distances. In 1831, we had
for this purpose flat rods, as they were called, rods transmitting
power from pumping engines for a considerable distance to the pits
where the pumps were placed, and we had also the pneumatic, the
exhaustion system--the invention of John Hague, a Yorkshire-man, my
old master, to whom I was apprenticed--which mode of transmission was
then used to a very considerable extent. The recollection of it, I
find, however, has nearly died out, and I am glad to have this
opportunity of reviving it. But in 1881, we have, for the transmission
of power, first of all, quick moving ropes, and there is not, so far
as I know a better instance of this system than that at Schaffhausen.
Any one who has ever, in recent years, gone a mile or two above the
falls at Schaffhausen, must have seen there--in a house, on the bank
of the Rhine, opposite to that on which the town is situated--large
turbines driven by the river, which is slightly dammed up for the
purpose. These work quick-going ropes, carried on pulleys, erected at
intervals along the river bank, for the whole length of the town; and
power is delivered from them to shafting below the streets, and from
it into any house where it is required for manufacturing purposes.
Then we have the compressed air transmission of power, which is very
largely used for underground engines, and for the working of rock
drills in mines and tunnels.

COMPRESSED AIR LOCOMOTIVES.

We have also compressed air in a portable form, and it is now employed
with great success in driving tram-cars. I had occasion last January
to visit Nantes, where, for eighteen months, tram-cars had been driven
by compressed air, carried on the cars themselves, coupled with an
extremely ingenious arrangement for overcoming the difficulties
commonly attendant on the use of compressed air engines. This consists
in the provision of a cylindrical vessel half filled with hot water
and half with steam, at a pressure of eighty pounds on the square
inch. The compressed air, on its way from the reservoir to the engine,
passes through the water and steam, becoming thereby heated and
moistened, and in that way all the danger of forming ice in the
cylinders was prevented, and the parts were susceptible of good
lubrication. These cars, which start every ten minutes from each end,
make a journey of 33/4 miles, and have proved to be a commercial and an
engineering success. I believe, moreover, that they are capable of
very considerable improvement.

HYDRAULIC TRANSMISSION OF POWER.

Then there is, although not much used, the transmitting of power by
means of long steam pipes. There is also the transmission
hydraulically. This may be carried out in an intermittent manner, so
as to replace the reciprocating flat rods of old days; that is to say,
if two pipes containing water are laid down, and if the pressure in
those pipes at the one end be alternated, there will be produced an
alternating and a reciprocative effect at the other, to give motion to
pumps or other machinery. There is also that thoroughly well known
mode of transmission, hydraulically, for which the engineering world
owes so much to our president. We have, by Sir William Armstrong's
system, coupled with his accumulator, the means of transmitting
hydraulically the power of a central motor to any place requiring it,
and by the means of the principal accumulator, or if need be by that
aided by local accumulators, a comparatively small engine is enabled
to meet very heavy demands made upon it for a short time. I think I am
right in saying that, at the ordinary pressure which Sir William
Armstrong uses in practice, viz., 700 lb. to the square inch, one foot
a second of motion along an inch pipe would deliver at the rate to
produce one-horse power. Therefore, a ten-inch pipe, with the water
traveling at no greater pace than three feet in a second, would
deliver 300 horse-power. This 300 horse-power would no doubt be
somewhat reduced by the loss in the hydraulic engine, which would
utilize the water. But the total energy received would be equivalent
to producing 300 horse-power. Such a transmission would be effected
with an exceedingly small loss infliction in transit. I believe I am
right in saying that a 10 inch pipe a mile long would not involve much
more than about 14 or 15 lb. differential pressure to propel the
water through it at the rate of three feet in a second. If that be so,
then, with 700 lb. to the inch, the loss under such circumstances
would be only two per cent. in transmission. There is no doubt that
this transmission of power hydraulically has been of the greatest
possible use. It has enabled work to be done which could not be done
before. Enormous weights are raised with facility wherever required,
as by the aid of power hydraulically transmitted, it is perfectly easy
for one man to manage the heaviest cranes. Moreover, as I have said in
other places, the system which we owe to Sir William Armstrong has
gone far to elevate the human race, and it has done so in this manner.
So long as it is competent for a man to earn a living by mere
unintelligent exercise of his muscles, he is very likely to do it. You
may see in the old London docks the crane-heads covered by structures
that look like paddle-boxes. If you go to them, there is, I am glad to
say, nothing now to fill them up; but when the British Association
first met, these paddle-boxes covered large tread-wheels, in which men
trod, so as to raise a weight. Now, although I know that in fact there
is nothing more objectionable in a man turning a wheel by treading
inside of it than there is if he turn it round by a winch-handle, yet
somehow it strikes one more as being merely the work of an animal, a
turnspit, or a squirrel, or, indeed, as the task imposed on the
criminal. But, nevertheless, in this way there were a large number of
persons getting their living by the mere exercise of their muscles,
but, as might be expected, a very poor living, derived as it was from
unintelligent labor. That work is no longer possible, and is not so,
for the powerful reason that it does not pay. Those persons,
therefore, who would now have been thus occupied, are compelled to
elevate themselves, and to become competent to earn their living in a
manner which is more worthy of an intelligent human being. It is on
these grounds that I say we owe very much the elevation of the working
classes, especially of the class below the artisan, to this invention
of our distinguished president.

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