Scientific American Supplement, No. 460, October 25, 1884 by Various
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Various >> Scientific American Supplement, No. 460, October 25, 1884
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_Table I.--Impact on Level Plate._
--------------+--------------------+----------+----------+----------
| Inclination of jet | | |
Distance. | to the horizonal. | 90 deg. | 60 deg. | 45 deg.
--------------+--------------------+----------+----------+----------
| | Pressure | Pressure | Pressure
| | | |
/ | Experiment \ | / | 61.00 | 49.00
11/2 in. < | > | 71.00 < | |
\ | Theory / | \ | 61.48 | 50.10
| | | |
| | | |
/ | Experiment \ | / | 55.00 | 45.00
1 in. < | > | 63.00 < | |
\ | Theory / | \ | 54.00 | 45.00
| | | |
--------------+--------------------+----------+----------+----------
In each case the unit of pressure is 1/4 oz.
In the first trial there was a distance of 11/2 in. between the jet and point
of its contact with the plate, while in the second trial this space was
diminished to 1/2 in. It will be noticed that as this distance increases we
have augmented pressures, and these are not due, as might be supposed, to
increase of head, which is practically nothing, but they are due to the
recoil of a portion of the stream, which occurs increasingly as it becomes
more and more broken up. These alterations in pressure can only be
eliminated when care is taken to measure that only due to impact, without
at the same time adding the effect of an imperfect reaction. Any stream
that can run off at all points from a smooth surface gives the minimum of
pressure thereon, for then the least resistance is offered to the
destruction of the vertical element of its velocity, but this freedom
becomes lost when a stream is diverted into a confined channel. As pressure
is an indication and measure of lost velocity, we may then reasonably look
for greater pressure on the scale when a stream is confined after impact
than when it discharges freely in every direction. Experimentally this is
shown to be the case, for when the same oblong jet, discharged under the
same conditions, impinged vertically upon a smooth plate, and gave a
pressure of 71 units, gave 87 units when discharged into a confined
right-angled channel. This result emphasizes the necessity for confining
streams of water whenever it is desired to receive the greatest pressure by
arresting their velocity. Such streams will always endeavor to escape in
the directions of least resistance, and, therefore, in a turbine means
should be provided to prevent any lateral deviation of the streams while
passing through their buckets. So with screw propellers the great mass of
surrounding water may be regarded as acting like a channel with elastic
sides, which permits the area enlarging as the velocity of a current
passing diminishes. The experiments thus far described have been made with
jets of an oblong shape, and they give results differing in some degree
from those obtained with circular jets. Yet as the general conclusions from
both are found the same, it will avoid unnecessary prolixity by using the
data from experiments made with a circular jet of 0.05 square inch area,
discharging a stream at the rate of 40 ft. per second. This amounts to 52
lb. of water per minute with an available head of 25 ft., or 1,300
foot-pounds per minute. The tubes which received and directed the course of
this jet were generally of lead, having a perfectly smooth internal
surface, for it was found that with a rougher surface the flow of water is
retarded, and changes occur in the data obtained. Any stream having its
course changed presses against the body causing such change, this pressure
increasing in proportion to the angle through which the change is made, and
also according to the radius of a curve around which it flows. This fact
has long been known to hydraulic engineers, and formulae exist by which such
pressures can be determined; nevertheless, it will be useful to study these
relations from a somewhat different point of view than has been hitherto
adopted, more particularly as they bear upon the construction of screw
propellers and turbines; and by directing the stream, AB, Fig. 3,
vertically into a tube 3/8 in. internal diameter and bent so as to turn the
jet horizontally, and placing the whole arrangement upon a compound
weighing machine, it is easy to ascertain the downward pressure, AB, due to
impact, and the horizontal pressures, CB, due to reaction. In theoretical
investigations it may be convenient to assume both these pressures exactly
equal, and this has been done in the paper "On Screw Propellers" already
referred to; but this brings in an error of no importance so far as general
principles are involved, but one which destroys much of the value such
researches might, otherwise possess for those who are engaged in the
practical construction of screw propellers or turbines. The downward impact
pressure, AB, is always somewhat greater than the horizontal reaction, BC,
and any proportions between these two can only be accurately ascertained by
trials. In these particular experiments the jet of water flowed 40 ft. per
second through an orifice of 0.05 square inch area, and in every case its
course was bent to a right angle. The pressures for impact and reaction
were weighed coincidently, with results given by columns 1 and 2, Table II.
[Illustration: FIG. 3]
[Illustration: FIG. 4]
_Table II.--Impact and Reaction in Confined Channels._
-----------------------------+-------+---------+----------+-------
Number of column. | 1 | 2 | 3 | 4
-----------------------------+-------+---------+----------+-------
Description of experiments. |Impact.|Reaction.|Resultant.| Angles
| | | | ABS.
-----------------------------+-------+---------+----------+-------
Smooth London tube, 13/4 in. | 71 | 62 | 94.25 | 49 deg.
mean radius. | | | |
| | | |
Rough wrought iron tube, | 78 | 52 | 98.75 | 56.5 deg.
13/4 in. | | | |
| | | |
Smooth leaden tube bent to a | 71 | 40 | 81.5 | 60
sharp right angle. | | | |
-----------------------------+-------+---------+----------+------
The third column is obtained by constructing a parallelogram of forces,
where impact and reaction form the measures of opposing sides, and it
furnishes the resultant due to both forces. The fourth column gives the
inclination ABS, at which the line of impact must incline toward a plane
surface RS, Fig. 3, so as to produce this maximum resultant perpendicularly
upon it; as the resultant given in column 3 indicates the full practical
effect of impact and reaction. When a stream has its direction changed to
one at right angles to its original course, and as such a changed direction
is all that can be hoped for by ordinary screw propellers, the figures in
column 3 should bear some relationship to such cases. Therefore, it becomes
an inquiry of some interest as to what angle of impact has been found best
in those screw propellers which have given the best results in practical
work. Taking one of the most improved propellers made by the late Mr.
Robert Griffiths, its blades do not conform to the lines of a true screw,
but it is an oblique paddle, where the acting portions of its blades were
set at 48 deg. to the keel of the ship or 42 deg. to the plane of rotation.
Again, taking a screw tug boat on the river Thames, with blades of a
totally different form to those used by Mr. Griffiths, we still find them
set at the same angle, namely, 48 deg. to the keel or 42 deg. to the plane
of rotation. An examination of other screws tends only to confirm these
figures, and they justify the conclusion that the inclinations of blades
found out by practice ought to be arrived at, or at any rate approached, by
any sound and reliable theory; and that blades of whatever form must not
transgress far from this inclination if they are to develop any
considerable efficiency. Indeed, many favorable results obtained by
propellers are not due to their peculiarities, but only to the fact that
they have been made with an inclination of blade not far from 42 deg. to
the plan of rotation. Referring to column 4, and accepting the case of
water flowing through a smooth tube as analogous to that of a current
flowing within a large body of water, it appears that the inclination
necessary to give the highest resultant pressure is an angle of 49 deg.,
and this corresponds closely enough with the angle which practical
constructors of screw propellers have found to give the best results.
Until, therefore, we can deal with currents after they have been
discharged from the blades of a propeller, it seems unlikely that anything
can be done by alterations in the pitch of a propeller. So far as concerns
theory, the older turbines were restricted to such imperfect results of
impact and reaction as might be obtained by turning a stream at right
angles to its original course; and the more scientific of modern turbine
constructors may fairly claim credit for an innovation by which practice
gave better results than theory seemed to warrant; and the consideration of
this aspect of the question will form the concluding subject of the present
paper. Referring again to Fig. 3, when a current passes round such a curve
as the quadrant of a circle, its horizontal reaction appears as a pressure
along _c_ B, which is the result of the natural integration of all the
horizontal components of pressures, all of which act perpendicularly to
each element of the concave surface along which the current flows. If, now,
we add another quadrant of a circle to the curve, and so turn the stream
through two right angles, or 180 deg., as shown by Fig. 4, then such a
complete reversal of the original direction represents the carrying of it
back again to the highest point; it means the entire destruction of its
velocity, and it gives the maximum pressure obtainable from a jet of water
impinging upon a surface of any form whatsoever. The reaction noticed in
Fig. 3 as acting along _c_ B is now confronted by an impact of the now
horizontal stream as it is turned round the second 90 deg. of curvature,
and reacts also vertically downward. It would almost seem as if the first
reaction from B to F should be exactly neutralized by the second impact
from F to D. But such is not the case, as experiment shows an excess of the
second impact over the first reaction amounting to six units, and shows
also that the behavior of the stream through its second quadrant is
precisely similar in kind to the first, only less in degree. Also the
impact takes place vertically in one case and horizontally in the other.
The total downward pressure given by the stream when turned 180 deg. is
found by experiment thus: Total impact and reaction from 180 deg. change in
direction of current = 132 units; and by deducting the impact 71 units, as
previously measured, the new reaction corresponds with an increase of 61
units above the first impact. It also shows an increase of 37.75 units
above the greatest resultant obtained by the same stream turned through 90
deg. only. Therefore, in designing a screw propeller or turbine, it would
seem from these experiments desirable to aim at changing the direction of
the stream, so far as possible, into one at 180 deg. to its original
course, and it is by carrying out this view, so far as the necessities of
construction will permit, that the scientifically designed modern turbine
has attained to that prominence which it holds at present over all
hydraulic motors. Much more might be written to extend and amplify the
conclusions that can be drawn from the experiments described in the present
paper, and from many others made by the writer, but the exigencies of time
and your patience alike preclude further consideration of this interesting
and important subject.
* * * * *
IMPROVED TEXTILE MACHINERY.
[Illustration: THE TEXTILE EXHIBITION, ISLINGTON.]
In the recent textile exhibition at Islington, one of the most extensive
exhibits was that, of Messrs. James Farmer and Sons, of Salford. The
exhibit consists of a Universal calender, drying machines, patent creasing,
measuring, and marking machines, and apparatus for bleaching, washing,
chloring, scouring, soaping, dunging, and dyeing woven fabrics. The purpose
of the Universal calender is, says the _Engineer_, to enable limited
quantities of goods to be finished in various ways without requiring
different machines. The machine consists of suitable framing, to which is
attached all the requisite stave rails, batching apparatus, compound
levers, top and bottom adjusting screws, and level setting down gear, also
Stanley roller with all its adjustments. It is furthermore supplied with
chasing arrangement and four bowls; the bottom one is of cast iron, with
wrought iron center; the next is of paper or cotton; the third of chilled
iron fitted for heating by steam or gas, and the top of paper or cotton. By
this machine are given such finishes as are known as "chasing finish" when
the thready surface is wanted; "frictioning," or what is termed "glazing
finish," "swigging finish," and "embossing finish;" the later is done by
substituting a steel or copper engraved roller in place of the friction
bowl. This machine is also made to I produce the "Moire luster" finish. The
drying machine consists of nineteen cylinders, arranged with stave rails
and plaiting down apparatus. These cylinders are driven by bevel wheels, so
that each one is independent of its neighbor, and should any accident occur
to one or more of the cylinders or wheels, the remaining ones can be run
until a favorable opportunity arrives to repair the damage. A small
separate double cylinder diagonal engine is fitted to this machine, the
speed of which can be adjusted for any texture of cloth, and being of the
design it is, will start at once on steam being turned one. The machine
cylinders are rolled by a special machine for that purpose, and are
perfectly true on the face. Their insides are fitted with patent buckets,
which remove all the condensed water. In the machine exhibited, which is
designed for the bleaching, washing, chloring, and dyeing, the cloth is
supported by hollow metallic cylinders perforated with holes and corrugated
to allow the liquor used to pass freely through as much of the cloth as
possible; the open ends of the cylinders are so arranged that nearly all of
their area is open to the action of the pump. The liquor, which is drawn
through the cloth into the inside of the cylinders by the centrifugal
pumps, is discharged back into the cistern by a specially constructed
discharge pipe, so devised that the liquor, which is sent into it with
great force by the pump, is diverted so as to pour straight down in order
to prevent any eddies which could cause the cloth to wander from its
course. The cloth is supported to and from the cylinders by flat perforated
plates in such a manner that the force of the liquor cannot bag or displace
the threads of the cloth, and by this means also the liquor has a further
tendency to penetrate the fibers of the cloth. Means are provided for
readily and expeditiously cleansing the entire machine. The next machine
which we have to notice in this exhibit is Farmer's patent marking and
measuring machine, the purpose of which is to stamp on the cloths the
lengths of the same at regular distances. It is very desirable that drapers
should have some simple means of discovering at a glance what amount of
material they have in stock without the necessity of unrolling their cloth
to measure it, and this machine seems to perfectly meet the demands of the
case. The arrangement for effecting the printing and inking is shown in our
engraving at A. It is contained within a small disk, which can be moved at
will, so that it can be adapted to various widths of cloth or other
material. A measuring roller runs beside the printing disk, and on this is
stamped the required figures by a simple contrivance at the desired
distances, say every five yards. The types are linked together into a
roller chain which is carried by the disk, A, and they ink themselves
automatically from a flannel pad. The machine works in this way: The end of
the piece to be measured is brought down until it touches the surface of
the table, the marker is turned to zero, and also the finger of the dial on
the end of the measuring roller. The machine is then started, and the
lengths are printed at the required distances until it becomes necessary to
cut out the first piecing or joint in the fabric. The dial registers the
total length of the piece.
* * * * *
ENDLESS ROPE HAULAGE.
In the North of England Report, the endless rope systems are classified as
No. 1 and No 2 systems. No. 1, which has the rope under the tubs, is said
to be in operation in the Midland counties. To give motion to the rope a
single wheel is used, and friction for driving the rope is supplied either
by clip pulleys or by taking the rope over several wheels. The diagram
shows an arrangement for a tightening arrangement. One driving wheel is
used, says _The Colliery Guardian_, and the rope is kept constantly tight
by passing it round a pulley fixed upon a tram to which a heavy weight is
attached. Either one or two lines of rails are used. When a single line is
adopted the rope works backward and forward, only one part being on the
wagon way and the other running by the side of the way. When two lines are
used the ropes move always in one direction, the full tubs coming out on
one line and the empties going in on the other. The rope passes under the
tubs, and the connection is made by means of a clamp or by sockets in the
rope, to which the set is attached by a short chain. The rope runs at a
moderately high speed.
[Illustration: TIGHTENING ARRANGEMENT--ENDLESS ROPE HAULAGE.]
No. 2 system was peculiar to Wigan. A double line of rails is always used.
The rope rests upon the tubs, which are attached to the rope either singly
or in sets varying in number from two to twelve. The other engraving shows
a mode of connection between the tubs and the rope by a rope loop as shown.
[Illustration: ATTACHMENT TO ENDLESS ROPE "OVER."]
The tubs are placed at a regular distance apart, and the rope works slowly.
Motion is given to the rope by large driving pulleys, and friction is
obtained by taking the rope several times round the driving pulley.
* * * * *
A RELIABLE WATER FILTER.
Opinions are so firmly fixed at present that water is capable of carrying
the germs of disease that, in cases of epidemics, the recommendation is
made to drink natural mineral waters, or to boil ordinary water. This is a
wise measure, assuredly; but mineral waters are expensive, and, moreover,
many persons cannot get used to them. As for boiled water, that is a
beverage which has no longer a normal composition; a portion of its salts
has become precipitated, and its dissolved gases have been given off. In
spite of the aeration that it is afterward made to undergo, it preserves an
insipid taste, and I believe that it is not very digestible. I have
thought, then, that it would be important, from a hygienic standpoint, to
have a filter that should effectually rid water of all the microbes or
germs that it contains, while at the same time preserving the salts or
gases that it holds in solution. I have reached such a result, and,
although it is always delicate to speak of things that one has himself
done, I think the question is too important to allow me to hold back my
opinion in regard to the apparatus. It is a question of general hygiene
before which my own personality must disappear completely.
In Mr. Pasteur's laboratory, we filter the liquids in which microbes have
been cultivated, so as to separate them from the medium in which they
exist. For this purpose we employ a small unglazed porcelain tube that we
have had especially constructed therefor. The liquid traverses the porous
sides of this under the influence of atmospheric pressure, since we cause a
vacuum around the tube by means of an air-pump. We collect in this way,
after several hours, a few cubic inches of a liquid which is absolutely
pure, since animals may be inoculated with it without danger to them, while
the smallest quantity of the same liquid, when not filtered, infallibly
causes death.
This is the process that I have applied to the filtration of water. I have
introduced into it merely such modifications as are necessary to render the
apparatus entirely practical. My apparatus consists of an unglazed
porcelain tube inverted upon a ring of enameled porcelain, forming a part
thereof, and provided with an aperture for the outflow of the liquid. This
tube is placed within a metallic one, which is directly attached to a cock
that is soldered to the service pipe. A nut at the base that can be
maneuvered by hand permits, through the intermedium of a rubber washer
resting upon the enameled ring, of the tube being hermetically closed.
Under these circumstances, when the cock is turned on, the water fills the
space between the two tubes and slowly filters, under the influence of
pressure, through the sides of the porous one, and is freed from all solid
matter, including the microbes and germs, that it contains. It flows out
thoroughly purified, through the lower aperture, into a vessel placed there
to receive it.
I have directly ascertained that water thus filtered is deprived of all its
germs. For this purpose I have added some of it (with the necessary
precautions against introducing foreign organisms) to very changeable
liquids, such as veal broth, blood, and milk, and have found that there was
no alteration. Such water, then, is incapable of transmitting the germs of
disease.
[Illustration: CHAMBERLAND'S WATER FILTER.]
With an apparatus like the one here figured, and in which the filtering
tube is eight inches in length by about one inch in diameter, about four
and a half gallons of water per day may be obtained when the pressure is
two atmospheres--the mean pressure in Mr. Pasteur's laboratory, where my
experiments were made. Naturally, the discharge is greater or less
according to the pressure. A discharge of three and a half to four and a
half gallons of water seems to me to be sufficient for the needs of an
ordinary household. For schools, hospitals, barracks, etc., it is easy to
obtain the necessary volume of water by associating the tubes in series.
The discharge will be multiplied by the number of tubes.
In the country, or in towns that have no water mains, it will be easy to
devise an arrangement for giving the necessary pressure. An increase in the
porosity of the filtering tube is not to be thought of, as this would allow
very small germs to pass. This filter being a perfect one, we must expect
to see it soil quickly. Filters that do not get foul are just the ones that
do not filter. But with the arrangement that I have adopted the solid
matters deposit upon the external surface of the filter, while the inner
surface always remains perfectly clean. In order to clean the tube, it is
only necessary to take it out and wash it vigorously. As the tube is
entirely of porcelain, it may likewise be plunged into boiling water so as
to destroy the germs that may have entered the sides or, better yet, it may
be heated over a gas burner or in an ordinary oven. In this way all the
organic matter will be burned, and the tube will resume its former
porosity.--_M. Chamberland, La Nature._
* * * * *
SIMPLE DEVICES FOR DISTILLING WATER.
The alchemists dreamed and talked of that universal solvent which they so
long and vainly endeavored to discover; still, for all this, not only the
alchemist of old, but his more immediate successor, the chemist of to-day,
has found no solvent so universal as water. No liquid has nearly so wide a
range of dissolving powers, and, taking things all round, no liquid
exercises so slight an action upon the bodies dissolved--evaporate the
water away, and the dissolved substance is obtained in an unchanged
condition; at any rate, this is the general rule.
The function of water in nature is essentially that of a solvent or a
medium of circulation; it is not, in any sense, a food, yet without it no
food can be assimilated by an animal. Without water the solid materials of
the globe would be unable to come together so closely as to interchange
their elements; and unless the temperatures were sufficiently high to
establish an igneous fluidity, such as undoubtedly exists in the sun, there
would be no circulation of matter to speak of, and the earth would be, as
it were, locked up or dead.
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