Scientific American Supplement, No. 430, March 29, 1884

V >> Various >> Scientific American Supplement, No. 430, March 29, 1884

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We may now consider the heating of blanks for stamping, hardening the
points of spindles, finishing the ends of umbrella tips, and work where
a small article, or a small part of any article, has to be heated to a
high temperature with speed and certainty. For these a long and narrow
flame is necessary, and I may mention that in cases where a high speed
of delivery is required, and a small part only has to be heated, such
as, for instance, in the hardening of the points of spindles for cotton
machinery, I have made burners giving a flame of exceedingly high
temperature only 1/4 inch wide and five feet long. This flame is produced
by the assistance of a blast of air, and is of sufficiently high
temperature to fuse the spindle in a few minutes.

The points only project over the flame, and the spindles are carried
mechanically at such a speed that at the end of the five feet traverse
they are red hot, and drop into water. More than one hundred are in the
flame at once, lying side by side.

For heating blanks for stamping, the furnace bar-burner is perfectly
suited, and in this work the chute supplying the blanks to the machine
should be made of two fireclay sides, with an opening for the flame
between the chute and flame being placed at a sharp angle, to prevent
risk of the blanks sticking or overriding each other. A blowpipe may
also be used with good effect, as shown in the above engraving, and in
many cases it is preferable and much easier to manage.

In some cases the direct contact of the flame would spoil the articles
to be heated, and instead of the arrangement mentioned, a tube of iron,
fireclay, or other suitable material is heated, and the articles are
passed through it. This system of continuous feed, through a tube, has
been applied to the firing of small articles of pottery, and might
possibly be well adapted, among other things, to the production of
gas-burners.

[Illustration: FIG. 4.]

Where the contact of air with the heated articles is injurious, many
plans have been tried to keep the ends closed as much as possible, but I
believe no more perfect and simple seal against the admission of air can
be devised than to turn a jet of pure gas, unmixed with air, into each
end of the tube. This is an absolute seal against the entry of oxygen in
an uncombined state; free oxygen cannot exist at a very high temperature
in the presence of coal gas.

For many trades there is a demand for hardened and tempered steel wire,
either round or flattened, and the production of this has led to many
attempts to obtain a satisfactory continuous process. The common method
now, which is worked as a "secret" process by most firms, is to pass
the wire through a tube to heat it, as already described, and to run it
direct from the tube through a hole in the side of a box filled with
oil, the whole being packed with asbestos, to prevent leakage; from this
it is passed through another similar hole on the opposite side, either
over a plate heated to the right temperature, or over a narrow open
flame of sufficient length and power to give the correct heat for
tempering.

Where absolute precision is necessary, the gas supply must be adapted by
an automatic regulator on the main, to prevent the slightest variation
of heat. Once adjusted, the production of flat and round spring wire by
the mile is an exceedingly simple matter. It is quite possible to obtain
absolute precision in temperature by a proper adjustment of the gas
pressure, and as this is, for tempering steel articles and some other
purposes, a matter of great importance, it is worth some consideration.
No pressure regulator alone will give an absolutely steady supply; but
if we put on first a regulator, adjusted to the minimum pressure of
supply, say one inch of water, and then fix another on the same pipe,
adjusted to a slightly lower pressure, say 9/10 of an inch, the first
regulator does the rough adjustment, and the second one will then give
an absolutely steady supply, provided always that the regulators are
both capable of passing more gas than is likely to be ever required. No
regulator can be relied on for absolute precision, if worked up to its
maximum possible capacity.

[Illustration: Fig. 5. ARRANGEMENT FOR HEATING BLANKS FOR STAMPING OR
HARDENING.]

Among other applications of a long narrow flame of high power, may be
mentioned the brazing of long lengths of tube, in fact the application
of flames of this form, with and without a blast of air, for different
temperatures, are almost endless.

The thousands of uses to which blowpipes are adapted are so well known,
that they need no mention, except the curiously ignored fact that the
power of any blowpipe depends on the air pressure. A compact flame of
high temperature cannot be obtained except with a heavy air pressure,
and the ignorance of this fact has caused an immense number of
unexplained failures. Many people think that one blower is as good as
another, and expect that a fan giving a pressure equal to, say, the
height of a two inch column of water should do the same work as a blower
giving a pressure ten to twenty times as great. The construction and
power of blowpipes, with the laws ruling the proportions and power, will
be found in an article on "Blowpipe Construction," published in _Design
and Work_, March, 1881, and as the matter is there fully treated, no
further reference to the subject is necessary.

In the more recent forms of gas-engine, the charge is exploded by a
wrought iron tube, heated to redness by the external application of a
gas flame. This, although considered satisfactory by the makers, appears
to me to be an exceedingly crude way of getting over the difficulty; and
I offer it as a suggestion, that a very small platinum tube shall be
used instead of iron. This, if made with a porous or spongy internal
coating, would fire the charge with certainty, at a lower temperature
than iron, and it could be made so thin and small in diameter, without
risk of deterioration or loss of strength, that an exceedingly small
flame could be used to heat it up. As it would be fully heated in a very
few seconds, the delay in starting would be obviated.

[Illustration: Fig. 6.]

There are many purposes for which a red heat is needed for slow
continuous processes on a small scale, such as case-hardening small
steel goods, annealing, heating light steel articles for hardening, and
a great variety of other similar processes. This, until recently, has
required the use either of a rather complicated furnace, or a blast of
air under pressure, to increase the rapidity of combustion. Since the
conclusion of my experiments on the theoretical construction of burners,
I have found that the high-power burners, previously described, are
capable of heating a crucible equal in size to their own diameter
to bright redness without the assistance of a chimney, provided the
crucible is protected from draughts by a fireclay cylinder.

This is an important point, as it renders the production of a continuous
bright red heat a matter of the greatest ease, even in crucibles of a
comparatively large size. Where the heat is steady, and certain not to
rise above a definite point, it can safely be used for such purposes as
hardening penknife blades and other articles which are very irregular
in thickness, the thin edges not being liable to be burnt or damaged by
overheating.

For the highest temperatures air under pressure is a necessity, as we
require a large quantity of gas burnt in as small a space as possible
with the maximum speed, and given this air supply, we are very little
hampered by conditions, as an explosive mixture may be blown through a
gauze into a fireclay chamber, closed, except so far as is necessary to
allow the escape or burnt gases. The speed of combustion is limited only
by the speed of supply of air and gas, and by increasing these there is
no practical limit to the heat which can be obtained. When we have to
do with the reduction of samples of refractory ores, testing the
comparative fusibility of different samples of firebricks, or alloys,
etc., the use of an explosive mixture blown into and burning in a
close chamber is invaluable, and the ease and certainty with which
any temperature may be obtained has led to great discoveries, and the
revolutionizing of many commercial processes. Recent experiments have
proved that, by a modification in the form of the well-known injector
furnace, an enormous increase of temperature may be obtained. I have,
in actual work, obtained the fusing point of cast iron in two minutes,
starting all cold, and have fused every furnace casing I have yet been
able to produce. If infusible casings can be made, I think I am not
overstating facts in saying that any temperature required can and will
eventually be obtained with the greatest ease. What the limit is I have
as yet not been able to discover.

There is one more application of gas, as a fuel, which, discovered and
published by myself some two years ago, has yet to become generally
known, and in some special processes may prove exceedingly valuable.
This is the addition of a very small quantity or coal gas, or light
petroleum vapors, to the air supplied by a blower or chimney pull,
to furnaces burning coke or charcoal. The instant and great rise in
temperature of the furnace, and the greater stability of the solid fuel
used, are extraordinary. This is, in fact, a practical application of
the well-known "flameless combustion," the only signs that the gas
is being burnt being a great rise in temperature and a decreased
consumption of the solid fuel; in fact, if the gas is in correct
proportion, the solid fuel remains unburnt, or nearly so, in spite of
the high temperature. In cases where a sudden rise in temperature is
required in a furnace, or where the power is deficient, this method
of supplementing and increasing the heat will be found of very great
service, and processes liable to be checked by making up a fire with
fresh fuel can be carried on without check, even after the solid fuel
has almost entirely disappeared.

That a solid fuel is quite unnecessary, I will prove in a very simple
manner, by burning a mixture of coal gas and air without a flame, in a
bundle of iron wire. The heat is sufficient to fuse the wrought iron
with ease, and the glare inside the bundle of wire is painful to the
eyes. The same result could be obtained by a pile of red-hot lumps of
firebrick, and the same heat obtained also without a trace of flame.

It is not possible to enter fully into such a wide and important subject
in a single lecture, and the suggestions now given are simply hints for
the guidance for those who need or desire to experiment. No doubt we
shall have, after a time, some text-books and other literature on this
subject, which is one of great importance to many industries; and it is
necessary for experimental work and applications to new industries, that
the experimenter shall not only be able to purchase special burners, but
that he shall have fundamental laws laid down which will enable him to
construct them for himself, so as to have his experiments under his own
control. The difficulty in the way of literature on the subject is that
those few who have worked in the matter are busy men, with little time
which is not already fully employed.

Pioneers on new ground have a great liability to generalize and jump at
conclusions, and the necessary exact work and detail must, to a great
extent, be left to those who follow on tracks already roughly marked
out.

Of the special trades which have come under my observation, I have only
had time to mention a very few. It appears to me that there are very few
manufacturing processes of any kind which could not be simplified by the
use of gas as a fuel, from the production of electric light apparatus
to the manufacture of explosives, cotton stockings, beer, catgut, glue,
umbrellas, ink, fish-hook, medals, stained glass windows, brushes, and
other trades equally various, which come daily under my own notice.

* * * * *

A man was received into the Laborisiere Hospital, Paris, the other day,
with a yard of rope hanging from his mouth. Traction upon the cord
revealed a section of clothes line measuring eight feet. He had been
surprised in an attempt at suicide and had tried to conceal his design
by swallowing the cord. He lived, of course--they generally do.

* * * * *

INSTANTANEOUS PHOTOGRAPHY.

A certain number of the readers of this journal are occupied with
photography, and all assuredly are interested in this marvelous art,
whose progress is so remarkable. So it has seemed to us that it would
be of interest to treat of a question that is the order of the day. We
desire to speak of those photographic apparatus called instantaneous
shutters.

Numerous apparatus of this kind have been proposed to the public, and
several even have been described in this journal, but we have to state
that, despite the success in certain cases, none of them has proved
remarkable for its qualities and superiority. This is due, we believe,
to the fact that inventors, while showing arrangements that were often
ingenious, have not always taken into account the end that the shutter
is to subserve, and the qualities that it must possess in order to
attain such end.

In face of the progress made by extra rapid dry processes, the question
of shutters has become the most important, since cabinet-making, optics,
and photographic chemistry give us apparatus, objectives, and products
which, although they will doubtless be improved upon, satisfy for the
present all our needs.

What is understood by instantaneousness? To our knowledge, no definition
thereof has as yet been given. For our part, we propose to style
"instantaneous" any photograph that is taken in a fraction of a second
that our senses will not permit us to estimate. The shutter is the
apparatus which allows the light to enter the photographic chamber
during this very short time.

In order to examine the different rules that govern the question of
shutters, we shall take as an example the type styled the "Guillotine."

This apparatus, as every one knows, is a stiff plate containing an
aperture and passing over the line of the rays of light. Some place
it in front and others behind, while others again place it within the
objective. Let us examine and discuss what occurs in the three cases.
Suppose a rectilinear objective of the kind most usually employed in
instantaneous photography, and an object, A B, that we wish to reproduce
(Fig. 1), the objective being provided with any sort of diaphragm. The
point, A, sends a bundle of rays, a"b", to the first lens. Here they are
slightly refracted, and then go on parallel lines to the second lens,
where they are again refracted and form at A' an image of A. It is this
image that we see upon the ground glass, and which makes an impression
upon the sensitive film. The point, B, behaves in the same way and
gives an image at B', but, as will be at once seen, the image will be
reversed. In our figure, A corresponds to the sky and B to the earth.
If, then, the shutter passes in front of the objective, it will first
allow of the passage of the rays which come from the sky, then, on
continuing its travel, it will unveil the landscape, and lastly the
ground. As it is submitted to the law of the fall of bodies and has a
uniformly increasing velocity, it follows that the time of exposure will
uniformly decrease between A' and B', and that the sky will pose longer
than the foreground. Such a result is contrary to all photographic
rules, which require that objects shall pose so much the longer the
less they are lighted. This position of the "guillotine" shutter is
absolutely false, and must be altogether discarded. If the shutter be
placed behind the objective, it will follow, as a consequence of the
same demonstration, that the time of exposure will go diminishing from
B' to A', and that the foreground will be exposed longer than the sky.
The solution is logical, then, and will permit of obtaining excellent
negatives.

[Illustration: FIG. 1]

Let us now examine how the image, A'B', is formed. The point, A, appears
first, and becomes lighter and lighter up to the moment at which all the
rays that emanate from the point, A, are unveiled. The point, B', is not
yet visible. As the shutter continues its travel the point, B', appears
in its turn and becomes illuminated like the point, A'. At this moment
the objective is completely uncovered; the image, A'B', is perfect, and
possesses its maximum intensity. Then the point, A', gradually becomes
obscured and disappears; and the same is the case with all parts of
A'B'. The image is developed progressively from A' to B', and makes its
impression upon the sensitive plate successively--a fact which, as
may be conceived, may have its importance. If, for example, we are
photographing a ship that is being tossed about by the sea (and we
borrow this example from our colleague, Mr. Davanne), the image of the
top of the mast will not be formed at the same instant as that of the
base, and if the motion of the mast has sufficient extent it may take on
a curved form, due to the fact that it has effected a movement between
the moments during which its apex and base were being photographed.

Upon placing the guillotine shutter in the optical center of the
objective, what will occur? The shutter will permit the passage of an
equal fraction of the rays derived from A and B, that is to say, the
image will be complete from the first instant of the exposure. The
points, A' and B', will be illuminated precisely at the same moment. As
the shutter continues its travel, a fresh quantity of rays coming from A
and B will be admitted, and the image will be illuminated more and more
up to the moment at which all the rays can pass. It will then possess
its maximum intensity. Then a portion of the rays from A and B being
intercepted, the image will become darker and darker until complete
extinction. The image here, then, is not produced successively as in the
former case, but is entire from the beginning. In this case the image of
our mast cannot be misshapen, since it has been accurately photographed
at the same moment.

The true place for the guillotine shutter, then, from a theoretical
standpoint, is in the interior of the objective. Are there any other
advantages to be gained by so placing it? Yes; it is easy to understand
that for the same time of exposure, and consequently for the same
result, the aperture may be so much the smaller in proportion as the
optical center is approached.

The luminous rays, in fact, form in the objective a double truncated
cone whose upper base is equal to the diaphragm, and the lower one to
the diameter of the lenses. If the aperture be equal to any diameter
whatever of one of the cones, the result will be the same; but, for
the same period of exposure, it will evidently prove advantageous to
approach the diaphragm. The ratio of the apertures that give the same
results at the optical center or behind the objective is as that of the
diaphragm employed to that of the back lens. If the diaphragm is
one centimeter and the lenses four centimeters, an aperture of one
centimeter in one case and of four in the other will give the same
result.

We shall see further along that it is advantageous to employ apertures
equal to several times the diameter of the diaphragm or lens. Now, from
what we have just said, an aperture, equal for example to four times the
diaphragm, will be only 4 centimeters, while the corresponding aperture
behind the lens must be 16. The dimensions of the first will be
practical, and those of the second will give too cumbersome and too
fragile an apparatus. But why must the aperture be larger than the
diaphragm employed? This is what we are going to demonstrate. Let us
make the aperture equal to the diameter of the objective, and see
what occurs at the different periods of the exposure. For the sake of
clearness, we shall suppose the velocity uniform.

It is evident, _a priori_, that a perfect apparatus will be the one that
will allow the light to act during the entire exposure with a maximum of
intensity. Is it thus, when the aperture is equal to the diameter of the
objective? Evidently not. Let us consult Fig. 2. We here see the shutter
progressively uncovering the objective. The light will increase from A
to C up to the moment when the objective is entirely uncovered, and will
then immediately decrease up to B. The objective has operated with a
maximum of light for only a short time. We are far from the ideal result
in which the maximum of light, CD, should exist during the entire
exposure, and form the upper plane precisely equal to AB.

[Illustration: Fig. 2.]

If we cannot obtain such a result in practice, we must nevertheless
aproximate to it. We shall do so by increasing the shutter. Up to C' the
apparatus will operate as before, but from C' to D' the aperture will be
complete, and from D' to B' will decrease as has been said.

Let us give A'B' the same value as AB, that is to say, let us increase
the velocity in the second case in order that the time of exposure shall
be the same; we shall at once see that in the first case the object will
be completely uncovered for only a very short time, while in the second
the exposure will be perfect for a very appreciable period.

The time of exposure which is absolutely active, we propose to call
effective time of exposure in contradistinction to the total time of the
same. The more we increase the value of C'D', that is to say, that of
the effective time, the more the ratio, C'D'/A'B', will approximate to
unity, and the nearer we shall reach perfection. The correlative of such
elongation of the aperture is an increase in velocity which will always
bring the total exposure to the same figure, whatever be the aperture
employed.

If the aperture be equal to two diameters, the effective time will be
equal to half the time of the total exposure; and if it is equal to
three diameters, the exposure will be good during 2/3 of the total time.
This amounts to saying that the effective time of exposure is equal to n
times the diameter--1, the velocity being supposed always uniform. If
we place the shutter within the objective, it is the diameter of the
diaphragm that it will be necessary to say. The effective time will be
equal then to n diaphragm--1.

From what precedes it results that in no case should the aperture be
inferior to the diaphragm, since the former would otherwise absolutely
suppress the effective time in giving a lower plane corresponding to
an insufficient quantity of light. Moreover, an aperature of this kind
would prove injurious to the quality of the image by successively
uncovering rays which do not form their image identically at the same
point. We are now, then, in presence of results that are absolutely
positive, and they are as follows:

1. The guillotine shutter should be placed in the interior of the
objective and as near as possible to optical center, that is to say,
behind the diaphragm, since the latter is precisely in the optical
center.

2. The aperture should be as wide as possible.

3. The velocity should be as great as possible.

In practice, an aperture from 4 to 5 times the diameter of diaphragm
employed will be more than sufficient, since we shall have, according to
circumstances, 3/4 or 4/5 of the effective time. Moreover, whatever be the
time of exposure, this ratio once established will be invariable, and
the apparatus will always operate identically.

A shutter combining these qualities will not yet be perfect. It is
necessary, according to the time and the light, that the time of
exposure shall be capable of being varied. In a word, it is necessary
that the apparatus shall be _graduated_ and permit of taking views more
or less quickly. The different velocities might be given to the
shutter by means of weights, rubber, or springs. The latter seem to be
preferable, since they permit in the first place of operating out of
the vertical; moreover, they are less fragile, and, through different
tensions, they permit of these graduations that we consider as
indispensable. For the current needs of practice 1/100 of a second is a
limit that seems to us sufficient as a maximum of rapidity. In order to
know the time of exposure obtained we employ the following method, which
permits of graduating an apparatus rapidly and with extreme precision:

A band of smoked paper is fixed upon the shutter, then a tuning-fork
provided with a small stylet resting against the paper is made to
vibrate. Better yet, a chronograph which vibrates synchronously with a
tuning-fork, whose motion is kept up by electricity, is put in the same
place. Fig. 3 shows the arrangement to be employed. We then let the
shutter fall, when the little stylet will inscribe a certain number of
vibrations. Knowing the number of vibrations of the tuning-fork, and
counting the number of those inscribed upon the paper, it is very simple
to deduce therefrom the amount of the time of exposure. The results of
one of these experiments we have reproduced in Fig. 4. The tuning-fork
gave 100 double vibrations per second. Six vibrations are included
between the opening and closing of the apparatus. Each vibration
estimated at 1/100 of a second. The exposure was 6/100 of a second in
round numbers. This is the amount of the total time of exposure. As
for that of the effective time, that is just as easily ascertained. It
suffices to know the number of vibrations comprised between the moment
at which one point of the objective has been completely uncovered and
that at which it has begun to be covered again. The time is equal to
2/100 in round numbers.

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