Scientific American Supplement, No. 492, June 6, 1885 by Various
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Various >> Scientific American Supplement, No. 492, June 6, 1885
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[Illustration: IMPROVED PLAITING MACHINE.]
To remedy this and to prevent its occurrence, Messrs. A. Edmeston and
Sons, Manchester, in the plaiting machines they are now manufacturing
make the upper gripper bar movable as well as the table below. Referring
to the illustration, the upper gripper bars, A A, are capable of moving
about the center pins, B B, and when the machine is working are operated
in the following manner:
Upon the shaft, C, which revolves in unison with the crank shaft working
the plaiting levers and knife, are placed two cams, D, one at each end,
inside the main frames. These cams engage with and work two escapement
levers or pallets, E E, upon which rest the feet of four rods, attached
one end to each of the upper gripper bars. Upon these four rods are
helical springs of sufficient strength to hold down, by means of the
grippers to which they are connected, the folds of cloth that have just
been made. The cam, D, is so shaped that when the advancing plaiting
knife and cloth reach the front edge of the gripper bar, the gripper is
raised from the table to admit them freely. The instant the end of the
stroke is reached the anchor pallet or lever, E, escapes from the cam,
and the gripper bar is suddenly forced on to the knife and cloth by the
springs before mentioned, securely retaining the piece in its position.
Simultaneously with the first of these motions the plaiting table itself
is lowered, and, when the plaiting knife reaches the end of its stroke,
is released by means of the levers and chains, F F, which are in
connection with the escapement pallets, E, and partake of their every
motion. These chains are so attached that they exert no effort upon the
table until the escapement lever is moved, thus permitting the plaiting
table to press upward against either one or both of the gripper bars with
the full force imparted to it by the weights and levers, G' G'. The
chains, furthermore, are also threaded over pulleys in such a manner that
they adjust themselves automatically to every position of the table and
to the different thicknesses which the folded cloth acquires.
It will be obvious from this description that in plaiting there is no
more strain put upon the cloth in placing it under the grip than is
necessary to draw it over the table from the feed rollers. This feature
insures perfect immunity from the dragging out of grip, as already
described, and renders the machine very useful for finishers and
makers-up, as the delicacy with which the cloth is handled prevents any
damage being done to the finish of the lightest fabrics. Double cloth
can, of course, be plaited by it equally well, and the precision and
uniformity with which the cloth is plaited makes the machine thoroughly
reliable as a cloth measurer.--_Tex. Manfr._
* * * * *
SELF-ACTING SHUTTLE GUARD.
[Illustration: SELF-ACTING SHUTTLE GUARD.]
The annexed illustration shows the essential parts of Hahlo and
Liebreich's improvement, the loom being now at work. The handrail,
shuttle race, and starting handle can be at once recognized, and the
shuttle guard will be seen in its proper position, which position it
rigidly retains as long as the loom is working, but on a stoppage the rod
swings back close underneath the handrail, and quite clear of the reed.
The mode in which this is accomplished we will endeavor to make clear.
The guard is connected to the starting lever by the arrangement shown,
consisting of a stud on the handle, on which, with the movement of the
slay, lever, a, slides. This lever, by means of another lever and a link,
is attached to the shuttle guard by the crank, b, which, by means of the
set screw in the boss, permits the shuttle guard to be adjusted in the
most convenient place. It will be observed that whenever the loom stops
working, whether it is stopped by hand or automatically, the hand lever
has to be moved, and this movement is communicated to the shuttle guard
by the mechanism just described, placing the guard rod beneath the hand
rail, and leaving the whole of the shuttle race free and unencumbered.
The act of starting the loom brings the guard again to the working
position without any extra act having to be performed by the weaver. The
action is entirely automatic, and the weaver has not anything to do that
she has not to do with the present unguarded looms. The arrangement
appeared to ourselves to be a very efficient one, and it has the merit
that the length of the guard can be made greater than the width of the
cloth, a further advantage that will be recognized by practical weavers.
* * * * *
RULER AND TRIANGLE FOR HATCHING.
The instrument shown in the cut is the invention of Mr. Maginnis, and is
designed for producing equidistant hatchings. It consists of a short
ruler, A, and a triangle, B, supposed to be one of 45 deg., but which may be
of any angle. The triangle carries two stops, c c, while the ruler is
provided with a conical piece, D, which is slotted, and is held by a
screw. The play that occurs between this conical slide and the stops
varies according to the position of the former.
[Illustration: RULER AND TRIANGLE FOR HATCHING.]
The apparatus operates as follows: In the figure, the stop to the right
being in contact with the piece, D, a line is drawn along the right side
of the triangle. Then the ruler is made to slide along the triangle until
D touches the other stop, and then the triangle is slid along the ruler
until the stop to the right touches D again. In this position another
line is drawn, and so on. The position of the piece, D, between the stops
is regulated according to the fineness of the hatching to be
done.--_Chronique Industrielle_.
* * * * *
THE DISTILLATION OF SEA WATER.
The supplying of the troops at Suakim and in the Soudan with water is one
of the most important items in the whole conduct of the Egyptian war.
Even in cold or temperate latitudes fresh water is a first necessity for
animal life; much more is this the case in the desert; and the wells in
the country forming the scene of our military operations form in
themselves valuable strategical points. Their supply, however, has to be
supplemented, and to do so artificial means and the aid of the engineer
have to be enlisted into this service.
Many of our readers see notices from time to time in the newspapers about
this or that ship being employed, or at least her steam fittings, in
distilling water for the use of the troops; and although most of, if not
all, our readers are engineers, still it is no disparagement to some of
them to assume that they are more or less unfamiliar with sea water
distillation on the scale on which the process is now being carried on at
Suakim; and as the subject is of general interest, we give a short
description of the process.
In a general sense, fresh water is obtained from sea water by simply
generating steam from the sea water, passing the said steam through a
surface condenser, and filtering the resulting water. The obtaining of
fresh water in this way has been in practice on board sea-going ships for
many years. It is supposed by some authorities on this subject that the
first time fresh water was thus obtained at sea was by an old captain of
a brig which ran short of water, and he cut up some pewter dishes into
strips, which he bent and soldered into a pipe. He, with the carpenter's
aid, fitted a wooden lid in one of the cooking boilers, and fixed one end
of his pipe in it. He next sawed a water cask in half, bored a hole in
the bottom of one half, and took his pipe through it, filling the space
round the pipe with sea water. Thus he extemporized a worm and still or
condenser. The distilled water, however, was scarcely drinkable. Not to
be beaten, however, the captain got some pieces of charred wood which he
put in the water, which so far improved it as to render it at all events
fit to sustain life, and our skipper brought his brig and her screw
safely to port. What suggested the use of charcoal to his mind history
does not tell. For many years past scarce any sea-going vessel leaves
port that is not fitted with a properly constructed distiller; and one
conspicuous advantage attending this practice is that each ship thus
fitted to the satisfaction of the Board of Trade inspector is allowed to
sail with only half the quantity of fresh water on board which she should
have if not provided with a distiller. The distiller and filter occupy
very much less space than that which would be occupied by the casks or
tanks of water otherwise required to be carried.
Coming now a little to detail, sea water distillers are usually fitted in
connection with the winch and its boiler, which latter supplies the steam
both for distillation and to drive the engine working its circulating
pump. Smaller distillers are worked without a pump, the cooling water
merely passing through by gravitation. These smaller affairs again are of
two kinds, the one being mounted at one end of the cooking hearth, as in
outline sketch, which shows a two oven hearth with distiller at one end.
A is the supply pipe to admit air to aerate the water; B is the cock
where fresh water is drawn off; C is a pipe conveying cooling water to
the condenser E, placed on three little feet on top of the boiler, F,
whose steam rises up a central pipe to the dome top, where it expands out
and returns downward through a number of tubes about 1 in. diameter, in
which it is condensed, collected in a bottom chamber, and drawn off
through the cock, B. A distiller of this size would make about thirty
gallons of fresh water per day. Very frequently a distiller, such as is
shown in the sketch, is mounted separately, and placed near the winch or
donkey boiler, which supplies it with steam, the lower part, F, being
then used as a filter. The diameter of E is from 15 in. to 18 in., the
outer casing being either iron or copper. Another form of distiller is
one like the above, but larger, and having a small donkey engine and
circulating pump attached thereto. As a rule these distillers are
vertical, but larger apparatus are arranged horizontally. To give our
readers some general idea of size, weight, and produce of water, we may
say that a plain cylindrical distiller, mounted on a square filter case,
measuring 3 ft. 9 in. high, weighing 41/2 cwt., will distill twelve gallons
per hour. A larger size, measuring 6 ft. 2 in. high, and weighing about
23 cwt., will give 85 gallons; while a still larger one, measuring 7 ft.
high and weighing 32 cwt., yields 150 gallons. These have no pumps. When
an engine and pump are fitted, the weight is increased from about 80 per
cent. in the smaller to 50 per cent. in the larger sizes. An immense
advantage attends the use of those distillers that are combined with a
winch boiler. Of course, the chief use of the winch is while in dock;
some use is made of it at sea to do heavy pulling and hauling, to wash
decks, and in case of emergency the circulating pump is used as a fire
engine. Were it not, however, for the distiller, the winch boiler would
simply be idle lumber at sea. The distiller, however, finds useful
employment for it, and has also this excellent effect, that as steam is
pretty constantly kept up for the distiller, in the evil event of a fire
the boiler is ready to work at once. In horizontal types of distiller an
engine and pump are mounted on a cast iron casing as a bed, and in this
casing is placed a number of tubes through which the steam passes to be
condensed, the whole being simply a surface condenser with engine and
pump above. Another type is that of a small single-flued horizontal
boiler with combustion chamber and twenty or thirty return tubes--in
fact, the present high-pressure marine boiler on a small scale. A boiler
of this sort, measuring 4 ft. to 5 ft. long, 3 ft. 9 in. to 4 ft. 6 in.
diameter, would have a horizontal donkey engine on a bed at its side, and
at the end of the engine a vertical cylindrical condenser.
[Illustration]
Few have done more, perhaps none so much, as Dr. Normandy to make sea
water distillation not only a success as a source of water supply, but
also to supply it at a minimum cost for fuel. He by a peculiar
arrangement of pipes embodied something of the regenerative system in his
apparatus, using the heat taken from one lot of steam to generate more,
and again the heat from this he used over again. The defect of his older
arrangements was undue complexity and consequent trouble to keep in
order.
As can be well imagined, the distillers in use at Suakim are on a much
more colossal scale, and owing to the now almost universal use of surface
condensers in ocean steamers, no great difficulty ought to attend the
adaptation of the boilers and condensers of one of our transports. One of
these full-powered steamers will indicate, say, 5,000 horse-power, and
assuming her engines to use 25 lb. of steam per indicated horse-power, or
21/4 gallons, she could distill some 12,000 gallons of water per hour. As
no appreciable pressure of steam need be maintained, the boilers would
suffer little from deposit, especially if regularly blown out. Hard
firing need not be resorted to; indeed, it would be injudicious, as, of
course, priming must be carefully guarded against. Of course, the salt
water distilled will affect the working, not exactly of the distillers,
but of the boilers. If the water in the harbor, as is not improbable, is
muddy, some method of filtering it before pumping it into the boilers
ought, if at all practicable, to be resorted to, for the twofold reason
of preserving the boiler plates from muddy deposit, and also to prevent
priming, which would certainly ensue from the use of muddy water. No
doubt the medical staff take care that the distilled water is alike
thoroughly aerated and efficiently filtered. The most successful method
of aerating is, we believe, to cause the current of steam as it enters
the condenser to suck in air by induced current along with it. The
filtering ought not to present any difficulty, as at all events sand
enough can be had. Charcoal, however, is another affair, and all
distilled water ought to be brought into contact with this substance.
Simple, however, as such an arrangement as this appears to be, practical
difficulties, which it is _said_ are insurmountable, stand in the way of
its adoption, and the distilled water produced for Egypt is made in
special apparatus, and various forms of condenser are employed, made
under various patents. The principle involved is, however, in all cases
the same. Steam is generated in one of the ships' boilers, and condensed,
filtered, and aerated in a special apparatus. The great objection to the
use of the ordinary surface condenser is that the main engines would, in
the majority of cases, have to be kept going, in order to pump the
distilled water out of the condenser, and to supply circulating water.
But it is easy to see that if engineers thought proper, this difficulty
could be readily got over. Separate circulating pumps, usually
centrifugal, are now freely used, and the addition of a special pump for
lifting the condensed water presents no difficulty whatever. While the
main engines are running, the withdrawal of much condensed water would
no doubt risk the safety of the boiler; but in the case of so-called
"distilling" ships, there need be no trouble incurred on this
score.--_The Engineer_.
* * * * *
AIDS TO CORRECT EXPOSURE ON PHOTOGRAPHIC PLATES.
[Footnote: We take from the Br. Jour. of Photo. the following interesting
paper read by W. Goodwin before the Glasgow and West of Scotland Amateur
Association.]
With good plates, and intelligent development, a practiced photographer
may within certain limits correct the effects of an over or under
exposure; but you have all, doubtless, found out that there is a correct
exposure, and that you cannot trespass very far on either side of it
without sacrificing something in the resulting negative.
MR. W.K. BURTON'S TABLE OF COMPARATIVE EXPOSURES
------------+--------------------+-------------------+-------------------------
| | Badly lighted| Portraits in bright
| | interiors,| diffused light
Aperture | +------------+ up | out of doors.
calculated | Landscape with | Fairly | to | /
on the | heavy foliage in | lighted | | / Portraits in
standard | foreground. | interiors | | / studio light
system +------+-------+ +------+ | | | /
of the | Sea |Open | | Under| | | | / Portraits
Photographic| and |land- | |trees,| | | | | in ordinary
Society. | sky. | scape.| |up to | | | | | room.
------------+------+-------+-----+------+-----+------+------+-----+------
| sec | sec | sec | m s | m s| h m | sec | m s| m s
No. 1, | 1/160| 1/50 | 1/8 | 0 10 | 0 10| 0 2 | 1/6 | 0 1| 0 4
or f/4 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 2, | 1/80 | 1/25 | 1/4 | 0 20 | 0 20| 0 4 | 1/3 | 0 2| 0 8
or f/5.657 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 4, | 1/40 | 1/12 | 1/2 | 0 40 | 0 40| 0 8 | 2/3 | 0 4| 0 16
or f/8 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 8, | 1/20 | 1/6 | 1 | 1 20 | 1 20| 0 16 | 1-1/3| 0 8| 0 32
or f/11.314 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 16, | 1/10 | 1/3 | 2 | 2 40 | 2 40| 0 32 | 2-2/3| 0 16| 1 4
or f/16 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 32, | 1/5 | 2/3 | 4 | 5 20 | 5 20| 1 4 | 5-1/3| 0 32| 2 8
or f/22.627 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 64, | 2/5 | 1-1/3 | 8 |10 40 |10 40| 2 8 |10-1/2| 1 4| 4 15
or f/32 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 128, | 4/5 | 2-2/3 | 16 |21 0 |21 0| 4 15 | 21 | 2 8| 8 30
or f/45.255 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 256, |1-1/2 | 5-1/2 | 32 |42 0 |42 0| 8 30 | 42 | 4 15|17 0
or f/64 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
The estimation of this correct exposure is probably the greatest
difficulty in photography, and it is particularly discouraging to find
plate after plate useless because the guess has been wide of the mark.
There are some here to-night who have spoiled so many plates that at last
they are prepared by experience for almost any contingency, and to those
I nave very little to say; but there are also many who are still in their
troubles, and I propose to tell them how the amount of guesswork required
may be reduced to a minimum.
The factors which govern exposure are: the subject of the picture, the
lens and its aperture, the rapidity of the plate, and last, but not by
any means least, the quality of the light by which the work is to be
done.
Let us consider each of these separately, and see if we cannot reduce any
of them to rule. In this respect the subject will be found somewhat
intractable. Scarcely two subjects will be found to send exactly the same
amount of light through the lens. However, a broad classification may be
made, and this has been done by Mr. Burton in his Table of Comparative
Exposures. A glance at this table will show how greatly the character of
the view may influence the time of exposure. Thus, with full aperture of
a rapid symmetrical, the exposure for open landscape is given as
one-twelfth of a second; when heavy foliage appears in the foreground,
half a second will be required; while, under trees, as much as forty
seconds may be needed.
The first aid I have to suggest is the use of such a table as Mr.
Burton's. Before we do anything more in this direction, we must consider
the influence of the lens and its diaphragms. In theory the single
landscape lens is more rapid than the doublet of equal aperture, but the
difference is so little that it may be disregarded in practice, and my
remarks will apply to both.
The rapidity of a lens depends mainly on its aperture and its focal
length. Thus a lens of twelve inches focus will require four times the
exposure of a six inch, with an equal sized diaphragm, and a quarter inch
diaphragm will require four times the exposure of a half inch when used
in the same lens.
The Photographic Society of Great Britain have recommended that the
diaphragms of all lenses should bear such relation to the focal length
that each should require exactly double the exposure of the next smaller.
Now, if we turn again to Mr. Burton's table, we shall find that it is
constructed on this principle, and that each stop is numbered so as to
show its exposure. Obviously, the most sensible thing would be to get a
set of stops made to correspond with this arrangement, but we will see
how we can construct a table for stops of any size.
First, if possible, find the equivalent focus of your lens. If it is made
by a known maker, you will find it in his price list, and if not, you may
calculate it for yourself by the rules given in the various text books,
provided you have a camera of pretty long focus. However, it will be near
enough for our purpose if you get a sharp image of the sun on a piece of
paper, and while you hold lens and paper, get some one to measure the
distance from the paper to the diaphragm aperture, or, in the case of a
single lens, to the center of the lens. Note down this focal length, and
proceed to measure your diaphragms in sixteenths of an inch.
Then, with pen and paper, proceed to divide the diameter of each stop
into the focus, and state the result as a fraction of the focus, thus
f/8. For example, a Ross half plate rapid symmetrical has a focal length
of 71/2 in.; for convenience reduce this to sixteenths=120. A diaphragm
measuring seven sixteenths will give the fraction f/17. Now let us see if
any of these stops correspond with Mr. Burton's. The first two in his
table will only be found in portrait lenses, but we shall probably find
one to correspond with the third, if we are using a doublet lens; with a
single lens we won't find any so large. Having picked out those that
correspond, and filled in the exposure for them, we have now to deal with
the odd sizes. Here is one, f/27, which is just half way between No. 16
and No. 32, but a moment's thought will show that as the exposure
increases as the square of the diameter, it won't do to take the exposure
half way between the two.
We have another factor to consider now: that is, the rapidity of the
plate. If you use plates by a maker who has a name to sustain, you may be
pretty confident that they are of fairly uniform rapidity, so after you
have got into the way of working any particular brand, the best thing you
can do is to stick to it. The exposures in our table are for plates of
medium rapidity in good spring light. In my own experience I find that
they just suit "thirty times" plates, or fifteen on the sensitometer; but
then I like a full exposure with slow development, and I know that others
find these exposures just right for "twenty times" plates developed in
the usual way. The most rapid plates in the market will not be overdone
with half the given exposures. It must always be borne in mind that an
error of a fraction of a second in either direction may be corrected in
development, and it is impossible to make a very serious error if you
refer to the table.
We come now to the light. If you depend on the eye entirely in judging
the quality of the light, it will sometimes play you tricks. The rays
which are most active on the plates are those which have the least effect
on the eye. We can, however, by chemical means arrive at an exact
estimate of the active power, and for this purpose an actinometer is
used. This is simply an arrangement whereby a piece of sensitized paper
is exposed and allowed to darken to a standard tint, and by the time it
takes to reach that tint the value of the light is judged. Capt. Abney
has, however, pointed out that ordinary sensitized paper is not suitable
for bromide plates, since there are conditions of light in which the
plates will be fairly rapid while the paper will be very slow. He gives a
formula for a bromide paper, which is treated with tannin in order to
absorb the bromine set free during exposure, otherwise the darkening
would be very slight. I used this paper for a while, but found it rather
slow. The tannin also turned brown on keeping for a week or so. I then
made some more, substituting for tannin potassium _nitrite_ (not
nitrate), which is colorless. This was an improvement, but still it was
just slow enough.
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