Scientific American Supplement, No. 417

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These latter examples have been taken from the art of metallurgy; and it
may of course be said that, considering the intimate relations between
that art and the science of chemistry, there can be no wonder if the
former is largely dependent for its progress on the latter. I will
therefore turn to what may appear the most concrete, practical, and
unscientific of all arts--that, namely, of the mechanical engineer; and
we shall find that even here examples will not fail us of the boons
which pure science has conferred upon the art of construction, nor even
perhaps of the reciprocal advantages which she has derived from the
connection.

The address of Mr. Westmacott, from which I have already taken my text,
supplies in itself more than one instance of the kind we seek--instances
emphasized by papers read at the meeting where the address was spoken.
Let us take, first, the manufacture of sugar from beetroot. This
manufacture was forced into prominence in the early years of this
century, when the Continental blockade maintained by England against
Napoleon prevented all importation of sugar from America; and it has now
attained very large dimensions, as all frequenters of the Continent must
be aware. The process, as exhaustively described by a Belgian engineer,
M. Melin, offers several instances of the application of chemical and
physical science to practical purposes. Thus, the first operation in
making sugar from beetroot is to separate the juice from the flesh, the
former being as much as 95 per cent. of the whole weight. Formerly this
was accomplished by rasping the roots into a pulp, and then pressing the
pulp in powerful hydraulic presses; in other words, by purely mechanical
means. This process is now to a large extent superseded by what is
called the diffusion process, depending on the well known physical
phenomena of _endosmosis_ and _exosmosis_. The beetroot is cut up into
small slices called "cossettes," and these are placed in vessels filled
with water. The result is that a current of endosmosis takes place from
the water toward the juice in the cells, and a current of exosmosis
from the juice toward the water. These currents go on cell by cell, and
continue until a state of equilibrium is attained. The richer the water
and the poorer the juice, the sooner does this equilibrium take place.
Consequently the vessels are arranged in a series, forming what is
called a diffusion battery; the pure water is admitted to the first
vessel, in which the slices have already been nearly exhausted, and
subtracts from them what juice there is left. It then passes as a thin
juice to the next vessel, in which the slices are richer, and the
process begins again. In the last vessel the water which has already
done its work in all the previous vessels comes into contact with fresh
slices, and begins the operation upon them. The same process has been
applied at the other end of the manufacture of sugar. After the juice
has been purified and all the crystallizable sugar has been separated
from it by boiling, there is left a mass of molasses, containing so much
of the salts of potassium and sodium that no further crystallization of
the yet remaining sugar is possible. The object of the process called
osmosis is to carry off these salts. The apparatus used, or osmogene,
consists of a series of trays filled alternately with molasses and
water, the bottoms being formed of parchment paper. A current passes
through this paper in each direction, part of the water entering the
molasses, and part of the salts, together with a certain quantity of
sugar, entering the water. The result, of thus freeing the molasses
from the salts is that a large part of the remaining sugar can now be
extracted by crystallization.

Another instance in point comes from a paper dealing with the question
of the construction of long tunnels. In England this has been chiefly
discussed of late in connection with the Channel Tunnel, where, however,
the conditions are comparatively simple. It is of still greater
importance abroad. Two tunnels have already been pierced through the
Alps; a third is nearly completed; and a fourth, the Simplon Tunnel,
which will be the longest of any, is at this moment the subject of
a most active study on the part of French engineers. In America,
especially in connection with the deep mines of the Western States,
the problem is also of the highest importance. But the driving of such
tunnels would be financially if not physically impossible, but for
the resources which science has placed in our hands, first, by the
preparation of new explosives, and, secondly, by methods of dealing with
the very high temperatures which have to be encountered. As regards the
first, the history of explosives is scarcely anything else than a record
of the application of chemical principles to practical purposes--a
record which in great part has yet to be written, and on which we cannot
here dwell. It is certain, however, that but for the invention of
nitroglycerine, a purely chemical compound, and its development in
various forms, more or less safe and convenient, these long tunnels
would never have been constructed. As regards the second point, the
question of temperature is really the most formidable with which the
tunnel engineer has to contend. In the St. Gothard Tunnel, just before
the meeting of the two headings in February, 1880, the temperature
rose as high as 93 deg. Fahr. This, combined with the foulness of the air,
produced an immense diminution in the work done per person and per horse
employed, while several men were actually killed by the dynamite gases,
and others suffered from a disease which was traced to a hitherto
unknown species of internal worm. If the Simplon Tunnel should be
constructed, yet higher temperatures may probably have to be dealt with.
Although science can hardly be said to have completely mastered these
difficulties, much has been done in that direction. A great deal of
mechanical work has of course to be carried on at the face or far end of
such a heading, and there are various means by which it might be done.
But by far the most satisfactory solution, in most cases at least, is
obtained by taking advantage of the properties of compressed air. Air
can be compressed at the end of the tunnel either by steam-engines,
or, still better, by turbines where water power is available. This
compressed air may easily be led in pipes to the face of the heading,
and used there to drive the small engines which work the rock-drilling
machines, etc. The efficiency of such machines is doubtless low, chiefly
owing to the physical fact that the air is heated by compression, and
that much of this heat is lost while it traverses the long line of pipes
leading to the scene of action. But here we have a great advantage from
the point of view of ventilation; for as the air gained heat while being
compressed, so it loses heat while expanding; and the result is that a
current of cold and fresh air is continually issuing from the
machines at the face of the heading, just where it is most wanted. In
consequence, in the St. Gothard, as just alluded to, the hottest parts
were always some little distance behind the face of the heading.
Although in this case as much as 120,000 cubic meters of air (taken
at atmospheric pressure) were daily poured into the heading, yet the
ventilation was very insufficient. Moreover, the high pressure which is
used for working the machines is not the best adapted for ventilation;
and in the Arlberg tunnel separate ventilating pipes are employed,
containing air compressed to about one atmosphere, which is delivered
in much larger quantities although not at so low a temperature.
In connection with this question of ventilation a long series of
observations have been taken at the St. Gothard, both during and since
the construction; these have revealed the important physical fact
(itself of high practical importance) that the barometer never stands at
the same level on the two sides of a great mountain chain; and so have
made valuable contributions to the science of meteorology.

Another most important use of the same scientific fact, namely, the
properties of compressed air, is found in the sinking of foundations
below water. When the piers of a bridge, or other structure, had to be
placed in a deep stream, the old method was to drive a double row of
piles round the place and fill them in with clay, forming what is
called a cofferdam. The water was pumped out from the interior, and the
foundation laid in the open. This is always a very expensive process,
and in rapid streams is scarcely practicable. In recent times large
bottomless cases, called caissons, have been used, with tubes attached
to the roof, by which air can be forced into or out of the interior.
These caissons are brought to the site of the proposed pier, and are
there sunk. Where the bottom is loose sandy earth, the vacuum process,
as it is termed, is often employed; that is, the air is pumped out from
the interior, and the superincumbent pressure then causes the caisson
to sink and the earth to rise within it. But it is more usual to employ
what is called the plenum process, in which air under high pressure
is pumped into the caisson and expels the water, as in a diving bell.
Workmen then descend, entering through an air lock, and excavate the
ground at the bottom of the caisson, which sinks gradually as the
excavation continues. Under this system a length of some two miles of
quay wall is being constructed at Antwerp, far out in the channel of the
river Scheldt. Here the caissons are laid end to end with each other,
along the whole curve of the wall, and the masonry is built on the top
of them within a floating cofferdam of very ingenious construction.

There are few mechanical principles more widely known than that of
so-called centrifugal force; an action which, though still a puzzle
to students, has long been thoroughly understood. It is, however,
comparatively recently that it has been applied in practice. One of the
earliest examples was perhaps the ordinary governor, due to the genius
of Watt. Every boy knows that if he takes a weight hanging from a string
and twirls it round, the weight will rise higher and revolve in a larger
circle as he increases the speed. Watt saw that if he attached such an
apparatus to his steam engine, the balls or weights would tend to rise
higher whenever the engine begun to run faster, that this action might
be made partly to draw over the valve which admitted the steam, and that
in this way the supply of steam would be lessened, and the speed would
fall. Few ideas in science have received so wide and so successful an
application as this. But of late years another property of centrifugal
force has been brought into play. The effect of this so-called force is
that any body revolving in a circle has a continual tendency to fly off
at a tangent; the amount of this tendency depending jointly on the mass
of the body and on the velocity of the rotation. It is the former of
these conditions which is now taken advantage of. For if we have a
number of particles all revolving with the same velocity, but of
different specific gravities, and if we allow them to follow their
tendency of moving off at a tangent, it is evident that the heaviest
particles, having the greatest mass, will move with the greatest energy.
The result is that, if we take a mass of such particles and confine them
within a circular casing, we shall find that, having rotated this casing
with a high velocity and for a sufficient time, the heaviest particles
will have settled at the outside and the lightest at the inside, while
between the two there will be a gradation from the one to the other.
Here, then, we have the means of separating two substances, solid
or liquid, which are intimately mixed up together, but which are of
different specific gravities. This physical principle has been taken
advantage of in a somewhat homely but very important process, viz., the
separation of cream from milk. In this arrangement the milk is charged
into a vessel something of the shape and size of a Gloucester cheese,
which stands on a vertical spindle and is made to rotate with a velocity
as high as 7,000 revolutions per minute. At this enormous speed the
milk, which is the heavier, flies to the outside, while the cream
remains behind and stands up as a thin layer on the inside of the
rotating cylinder of fluid. So completely does this immense speed
produce in the liquid the characteristics of a solid, that if the
rotating shell of cream be touched by a knife it emits a harsh, grating
sound, and gives the sensation experienced in attempting to cut a stone.
The separation is almost immediately complete, but the difficult point
was to draw off the two liquids separately and continuously without
stopping the machine. This has been simply accomplished by taking
advantage of another principle of hydromechanics. A small pipe opening
just inside the shell of the cylinder is brought back to near the
center, where it rises through a sort of neck and opens into an exterior
casing. The pressure due to the velocity causes the skim milk to rise in
this pipe and flow continuously out at the inner end. The cream is at
the same time drawn off by a similar orifice made in the same neck and
leading into a different chamber.

Centrifugal action is not the only way in which particles of different
specific gravity can he separated from each other by motion only. If
a rapid "jigging" or up-and-down motion be given to a mixture of such
particles, the tendency of the lighter to fly further under the action
of the impulse causes them gradually to rise to the upper surface; this
surface being free in the present case, and the result being therefore
the reverse of what happens in the rotating chamber. If such a mixture
be examined after this up-and down motion has gone on for a considerable
period, it will be found that the particles are arranged pretty
accurately in layers, the lightest being at the top and the heaviest
at the bottom. This principle has long been taken advantage of in such
cases as the separation of lead ores from the matrix in which they are
embedded. The rock in these cases is crushed into small fragments, and
placed on a frame having a rapid up-and-down-motion, when the heavy lead
ore gradually collects at the bottom and the lighter stone on the top.
To separate the two the machine must be stopped and cleared by hand. In
the case of coal-washing, where the object is to separate fine coal from
the particles of stone mixed with it, this process would be very costly,
and indeed impossible, because a current of water is sweeping through
the whole mass. In the case of the Coppee coal-washer, the desired
end is achieved in a different and very simple manner. The well known
mineral felspar has a specific gravity intermediate between that of the
coal and the shale, or stone, with which it is found intermixed. If,
then, a quantity of felspar in small fragments is thrown into the
mixture, and the whole then submitted to the jigging process, the result
will be that the stone will collect on the top, and the coal at the
bottom, with a layer of felspar separating the two. A current of water
sweeps through the whole, and is drawn off partly at the top, carrying
with it the stone, and partly at the bottom, carrying with it the fine
coal.

The above are instances where science has come to the aid of
engineering. Here is one in which the obligation is reversed. The rapid
stopping of railroad trains, when necessary, by means of brakes, is a
problem which has long occupied the attention of many engineers; and the
mechanical solutions offered have been correspondingly numerous. Some
of these depend on the action of steam, some of a vacuum, some of
compressed air, some of pressure-water; others again ingeniously utilize
the momentum of the wheels themselves. But for a long time no effort
was made by any of these inventors thoroughly to master the theoretical
conditions of the problem before them. At last, one of the most
ingenious and successful among them, Mr. George Westinghouse, resolved
to make experiments on the subject, and was fortunate enough to
associate with himself Capt. Douglas Galton. Their experiments, carried
on with rare energy and perseverance, and at great expense, not only
brought into the clearest light the physical conditions of the question
(conditions which were shown to be in strict accordance with theory),
but also disclosed the interesting scientific fact that the friction
between solid bodies at high velocities is not constant, as the
experiments of Morin had been supposed to imply, but diminishes rapidly
as the speed increases--a fact which other observations serve to
confirm.

The old scientific principle known as the hydrostatic paradox, according
to which a pressure applied at any point of an inclosed mass of liquid
is transmitted unaltered to every other point, has been singularly
fruitful in practical applications. Mr. Bramah was perhaps the first
to recognize its value and importance. He applied it to the well known
Bramah press, and in various other directions, some of which were less
successful. One of these was a hydraulic lift, which Mr. Bramah proposed
to construct by means of several cylinders sliding within each other
after the manner of the tubes of a telescope. His specification of
this invention sufficiently expresses his opinion of its value, for it
concludes as follows: "This patent does not only differ in its nature
and in its boundless extent of claims to novelty, but also in its claims
to merit and superior utility compared with any other patent ever
brought before or sanctioned by the legislative authority of any
nation." The telescope lift has not come into practical use; but lifts
worked on the hydraulic principle are becoming more and more common
every day. The same principle has been applied by the genius of Sir
William Armstrong and others to the working of cranes and other machines
for the lifting of weights, etc.; and under the form of the accumulator,
with its distributing pipes and hydraulic engines, it provides a store
of power always ready for application at any required point in a large
system, yet costing practically nothing when not actually at work. This
system of high pressure mains worked from a central accumulator has
been for some years in existence at Hull, as a means of supplying power
commercially for all the purposes needed in a large town, and it is
at this moment being carried out on a wider scale in the East End of
London.

Taking advantage of this system, and combining with it another
scientific principle of wide applicability, Mr. J.H. Greathead has
brought out an instrument called the "injector hydrant," which seems
likely to play an important part in the extinguishing of fires. This
second principle is that of the lateral induction of fluids, and may be
thus expressed in the words of the late William Froude: "Any surface
which in passing through a fluid experiences resistance must in so doing
impress on the particles which resist it a force in the line of motion
equal to the resistance." If then these particles are themselves part
of a fluid, it will result that they will follow the direction of the
moving fluid and be partly carried along with it. As applied in the
injector hydrant, a small quantity of water derived from the high
pressure mains is made to pass from one pipe into another, coming in
contact at the same time with a reservoir of water at ordinary pressure.
The result is that the water from the reservoir is drawn into the second
pipe through a trumpet-shaped nozzle, and may be made to issue as
a stream to a considerable height. Thus the small quantity of
pressure-water, which, if used by itself, would perhaps rise to a height
of 500 feet, is made to carry with it a much larger quantity to a much
smaller height, say that of an ordinary house.

The above are only a few of the many instances which might be given to
prove the general truth of the fact with which we started, namely, the
close and reciprocal connection between physical science and mechanical
engineering, taking both in their widest sense. It may possibly be worth
while to return again to the subject, as other illustrations arise.
Two such have appeared even at the moment of writing, and though their
practical success is not yet assured, it may be worth while to cite
them. The first is an application of the old principle of the siphon to
the purifying of sewage. Into a tank containing the sewage dips a siphon
pipe some thirty feet high, of which the shorter leg is many times
larger than the longer. When this is started, the water rises slowly and
steadily in the shorter column, and before it reaches the top has left
behind it all or almost all of the solid particles which it previously
held in suspension. These fall slowly back through the column and
collect at the bottom of the tank, to be cleared out when needful. The
effluent water is not of course chemically pure, but sufficiently so
to be turned into any ordinary stream. The second invention rests on
a curious fact in chemistry, namely, that caustic soda or potash will
absorb steam, forming a compound which has a much higher temperature
than the steam absorbed. If, therefore, exhaust-steam be discharged
into the bottom of a vessel containing caustic alkali, not only will it
become condensed, but this condensation will raise the temperature of
the mass so high that it may be employed in the generation of fresh
steam. It is needless to observe how important will be the bearing of
this invention upon the working of steam engines for many purposes,
if only it can be established as a practical success. And if it is so
established there can be no doubt that the experience thus acquired will
reveal new and valuable facts with regard to the conditions of chemical
combination and absorption, in the elements thus brought together.

WALTER R. BROWNE.

* * * * *

HYDRAULIC PLATE PRESS.

One of the most remarkable and interesting mechanical arrangements at
the Imperial Navy Yard at Kiel, Germany, is the iron clad plate bending
machine, by means of which the heavy iron clad plates are bent for the
use of arming iron clad vessels.

Through the mechanism of this remarkable machine it is possible to bend
the strongest and heaviest iron clad plates--in cold condition--so that
they can be fitted close on to the ship's hull, as it was done with the
man-of-war ships Saxonia, Bavaria, Wurtemberg, and Baden, each of which
having an iron strength of about 250 meters.

[Illustration: IMPROVED HYDRAULIC PLATE PRESS.]

One may make himself a proximate idea of the enormous power of pressure
of such a machine, if he can imagine what a strength is needed to bend
an iron plate of 250 meters thickness, in cold condition; being also 1.5
meters in width, and 5.00 meters in length, and weighing about 14,555
kilogrammes, or 14,555 tons.

The bending of the plates is done as follows: As it is shown in the
illustration, connected herewith, there are standing, well secured into
the foundation, four perpendicular pillars, made of heavy iron, all
of which are holding a heavy iron block, which by means of female nut
screws is lifted and lowered in a perpendicular direction. Beneath the
iron block, between the pillars, is lying a large hollow cylinder in
which the press piston moves up and down in a perpendicular direction.
These movements are caused by a small machine, or, better, press
pump--not noticeable in the illustration--which presses water from
a reservoir through a narrow pipe into the large hollow cylinder,
preventing at the same time the escape or return of the water so forced
in. The hollow cylinder up to the press piston is now filled with water,
so remains no other way for the piston as to move on to the top. The
iron clad plate ready to undergo the bending process is lying between
press piston and iron block; under the latter preparations are already
made for the purpose of giving the iron clad plate such a form as it
will receive through the bending process. After this the press piston
will, with the greatest force, steadily but slowly move upward, until
the iron clad plate has received its intended bending.

Lately the hydraulic presses are often used as winding machines, that
is, they are used as an arrangement to lift heavy loads up on elevated
points.

The essential contrivance of a hydraulic press is as follows:

One thinks of a powerful piston, which, through, human, steam, or water
power, is set in a moving up-and-down motion. Through the ascent of the
piston, is by means of a drawing pipe, ending into a sieve, the water
absorbed out of a reservoir, and by the lowering of the piston water is
driven out of a cylinder by means of a narrow pipe (communication pipe)
into a second cylinder, which raises a larger piston, the so-called
press piston. (See illustration.)

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