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

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

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In the experiment in question, with an aperture equal to twice the
diameter of the diaphragm, we have, then, 1/3 of the half-open exposure;
and the amount of the effective time is 1/3. The difference that we
have in practice is due to the fact that the velocity is uniformly
accelerated. In order to increase the amount of the effective time, it
will be only necessary to increase the aperture of the shutter and apply
again the method that we have just pointed out.

[Illustration: FIG. 3.]

So much for the material part of the apparatus. It will be necessary
in addition to acquire sufficient individual experience to be able to
estimate the intensity of the light, and consequently to judge of the
diaphragm to be employed and the velocity to be obtained. It must not
be forgotten that such or such an object having a relatively slow speed
will not be sufficiently sharp on the negative if it is too near
the apparatus, while such or such another, much more rapid, might
nevertheless be caught if sufficient distance intervened. Here it is
that will appear the skill of the amateur, who will find it possible to
obtain the said object as large as possible and with a maximum degree of
sharpness.

We have seen what diverse qualities should be possessed by a good
guillotine shutter, and it is evident that the same should be found
in all apparatus of the kind. In our opinion the guillotine is a well
defined type that possesses one capital advantage, and that is that it
permits of the use of aperatures as wide as may be desired for the
same time of exposure. It is a question, as we have seen, of velocity.
Consequently, however short the exposure be, it will always be possible
to operate with a full amount of light during the greater part of the
exposure. It is necessary to dwell upon this point, since in another
kind of apparatus that possesses a closing and opening shutter the same
result cannot be reached. In the Boca apparatus, for instance, we remark
that at a given moment the time of exposure is reduced to nothing, as
the closing shutter covers the objective before the latter has been
unmasked by the opening one. In all exposures, in fact, the times of
opening and closing have a constant value. It follows that the shorter
the exposure is, the greater becomes such value, and to such a point
that, at a given moment, the apparatus no longer make an exposure.

[Illustration: FIG. 4.]

In the guillotine, on the contrary, the same space always intervenes
between the time of opening and closing, since it is fixed in an
unvarying manner by the diameter at the aperature. Then, the greater the
velocity, the more the time of opening and closing diminishes. If
the ratio of the effective to the total time of exposure is 3/4, for
example, it will be invariable, whatever be the velocity.

In concluding, we will remark that, without employing springs, we
may increase the aperture of the shutter without varying the time of
exposure. To effect this it is only necessary to raise the point of the
shutter's drop. In fact, as may be seen in Fig. 4, all the vibrations
of the stylet corresponding to 1/100 of a second always continue to
elongate, and it will consequently be possible for the same time of
exposure to considerably increase the aperture and, as a consequence,
the effective time, by causing the guillotine to drop from a greater
elevation. From this study, which has principally concerned the
guillotine shutter, can we draw the deduction that this type of
apparatus will become a definite one? We think not. In fact, along with
its decided advantages the guillotine has a few defects that cannot be
passed over in silence. The aperture, in measure as it is increased,
renders the apparatus delicate and subject to become bent. If, in order
to obviate this trouble, we employ plates of steels, we increase its
weight considerably, and the chamber becomes subject to vibration at the
moment the shutter drops. If rubber or springs are used for increasing
the velocity, it is still worse. Moreover, it is quite difficult to
obtain a graduation, and to our knowledge, and probably for this reason,
it has not yet been applied.

The reader will please excuse us for this perhaps somewhat dry
theoretical _expose_, but we have thought it well to give it in the
hope that it might well show the qualities that should be required of a
photographic shutter and particularly of the guillotine. Moreover, at
the point to which photography has arrived it is no longer permitted to
do things by halves.

After the memorable discoveries of Nicephore, Niepce, Daguerre, and
Talbot, photography remained for some time stationary, limited to the
production of portraits and landscapes. But for a few years past it has
taken a new impetus, and new processes have come to the surface. In the
graphic arts and in the sciences it has taken considerable place. Being
the daughter of chemistry and physics, it is not astonishing that we
require of it the precision of both. It is, moreover, through a profound
study of the reactions that gave it birth and through a knowledge of the
laws of optics that it has come into current use in laboratories. In
fact, it alone is capable of giving with an undoubted character of
truthfulness a durable vestige of certain fleeting phenomena.--

_A. Londe, in La Nature_.

* * * * *

FALCONETTI'S CONTINUOUSLY PRIMED SIPHON.

To carry a watercourse over a canal, river, road, or railway, several
methods may be employed, as, for example, by aqueducts like those of
Arcueil and Buc near Versailles, and by upright and inverted siphons.
Of these three means, the first is the most imposing, but is also very
costly; and, besides, the declivities as well as the arrangement of the
ground are not always adapted thereto. The inverted siphon is subject
to obstruction and choking up in its most inaccessible parts, while
the upright siphon is easy of inspection, taking apart, etc. But, _per
contra_, the latter loses its priming very easily by reason of the
formation of air spaces.

[Illustration: FALCONETTI'S SIPHON.]

Mr. Falconetti, an inspector of bridges and roadways, has found a means
of rendering the latter occurrence impossible by an arrangement which
is both simple and practical, and which is illustrated herewith. In the
figure, a and b are the two vertical legs of the siphon, both of which
enter the liquid. These open into the receptacles, c and d, in which the
cocks, e and f, cut off or set up a communication with the pipes, a
and b. These latter are connected by a branch, g, which may be put in
communication with a reservoir, h, that is divided into two superposed
compartments by a partition, i. Such communication may be established
or cut off by a valve, j, maneuvered by a key, k, which traverses
an aperture in the partition, i. Another aperture, m, in this same
partition serves to put the two parts of the reservoir, h, in
communication, and, for this purpose, is provided with a cock, n, which
is easily maneuvered from the exterior.

The object of this arrangement of cocks and reservoir is to prevent the
siphon from losing its priming through the possible presence in the
transverse portion of a certain quantity of air or gas that might be
given off by the water and accumulate in this place.

The compartment, A, of the reservoir, h, is designed for receiving the
gases that collect in the top of the siphon, while the upper compartment
contains water for making a hydraulic joint, and consequently preventing
any re-entrance of air through the apertures in the partition, i.

To prime the siphon, we shut the cocks, e and f, open the valves, j and
m, and pour in water until the whole affair (siphon and reservoir) is
full; then we close the cock, m, and open the three others. The siphon
thus becomes primed, and begins to operate as soon as any water reaches
one or the other of the lower receptacles. As the cock, j, is constantly
turned on during the operation of the siphon, the air that has been able
to accumulate in the lower compartment, A, of the reservoir, h, would
finally unprime the siphon by intercepting communication between its two
legs. In order to prevent such a thing from occurring, it suffices to
expel the air, from time to time, that accumulates in the chamber,
A, this being done, without stopping the operation of the siphon, as
follows:

After closing the cock, j, water is poured into the reservoir, and,
running down to the lower compartment, drives out the air through the
cock, m. This operation once effected, it only remains to turn off the
cock, m, again, and open j in order to establish the normal operation.
As the chamber, A, is provided externally with a water gauge, N, it may
be seen at a glance when it is necessary to maneuver the cocks in order
to expel the air.

This system of siphon is evidently applicable to all sorts of liquids.
It may likewise undergo a few modifications in its construction; for
example, the valve, which in our engraving is placed over the siphon,
may be located at any distance from the apparatus, although it should,
in all cases, be in constant communication with it by means of a tube,
and be placed a little higher than the siphon. It may then be put under
cover and be kept constantly in sight, thus greatly facilitating its
surveillance.

As may be seen, the essential peculiarity of this improvement consists
in the very ingenious arrangement that permits of immersing the cocks in
the liquid to make them perfectly tight, it being necessary that they
should be hermetically closed in order to prevent the entrance of air
to the siphon. Everything leads to the belief, then, that if upright
siphons have never been able to operate regularly, it has been because
no means have been known of expelling the air from the interior without
letting air from the exterior enter at the same time. The arrangement
devised by Mr. Falconetti gets over the difficulty in a very elegant
manner. It seems as if it would be called upon to render great services
in the industries, and it well merits the attention of engineers
of roads and bridges, and of contractors on public works.--_Revue
Industrielle_.

* * * * *

THE WEIBEL-PICCARD SYSTEM OF EVAPORATING LIQUIDS.

In the industries, there are often considerable quantities of liquid to
be evaporated in order to concentrate it. Such evaporation is very often
performed by burning fuel in sufficient quantity to furnish the liquid
the heat necessary to convert it into steam. This process is attended
with a consumption of fuel such as to form a very important factor in
the cost of the product to be obtained. In order to vaporize, at the
pressure of the atmosphere, 1 kilogramme of water at 0 deg., 637 heat units
are required, and of these, 100 are employed in raising the water from
0 deg. to 100 deg. and 537 in converting the water at 100 deg. into steam at 100 deg..
This second quantity is called the _latent heat_ of the steam at 100 deg..
The sum of the two quantities is called the _total heat_ of the steam at
100 deg.. The total heat of the steam remains nearly constant, whatever be
the temperature at which the vaporization occurred.

[Illustration: THE WEIBEL-PICCARD EVAPORATION APPARATUS.]

In order to utilize the steam as a means of heating, it is necessary to
condense it, that is to say, to cause it to pass from the gaseous to a
liquid state. This conversion disengages as much heat as the passage
from the liquid to the gaseous state had absorbed.

It results from this that if we could condense the steam that is given
off by a liquid that we are vaporizing, in contact with another liquid
that it is also a question of vaporizing, we should utilize all the heat
contained in the steam that was being given off from the first.

This object can be practically attained by two means, viz., by (1)
putting the disengaged steam in contact with the sides of a vessel that
contains a liquid colder than the one that produced it; (2) by raising
the temperature and pressure of the disengaged steam in order to
condense it in contact with the sides of the vessel which contains the
very liquid that has produced it.

The first of these means is realized in the apparatus called multiple
acting, that are at present so generally employed in sugar works. The
second means, which permits of a greater saving in fuel being made than
the other does, is realized by compressing the disengaged steam. This
compression, which raises the temperature and pressure of the steam,
permits of condensing the latter in contact with the vessel wherein it
has been produced. By such condensation we continuously restore to the
liquid which is being vaporized the heat of the steam which it gives
off.

This solution of the question, which has been partially seen at
different epochs, has but recently made its way into the industries. It
is being operated at present with complete success at the salt works of
France and Switzerland, at those of Austria and Prussia, in the sugar
of milk factories of France and Switzerland, and, finally, in 1882, the
first application of it in the sugar industry was made at Pohrlitz, in
Moravia.

The saving of fuel that has been made in these different applications
has always been great.

We shall now, for the sake of explaining the system, give a brief
description of the apparatus as used at the Pohrlitz sugar works
mentioned above. These works treat 255 tons of beets per 24 hours, and
obtain 4,000 hectoliters of juice, which is reduced to about 1,000
hectoliters of sirup. Up to the present, the concentration has been
effected in a double acting apparatus partly supplied by exhaust steam
from the motive engines and partly by steam coming directly from the
generators.

In order to diminish the consumption of direct steam, these sugar works
put in a Weibel-Piccard apparatus designed to concentrate only a third
of their juice, or about 1,350 hectoliters per day.

This apparatus (see engraving) consists of a steam compressor, 0.835 m.
in diameter, actuated directly by a driving cylinder of 0.5 m. diameter
and 0.8 m. stroke, and of three evaporating boilers of the ordinary
vertical tube type, the first of which has a surface of 150 square
meters, the second 60, and the third 80.

The steam, at the ordinary pressure of the generators, say 5
atmospheres, is taken from the connected generators of the works, and is
led to the driving cylinder, where it expands and furnishes the power
necessary to run the compressor. It then escapes at a pressure of l.4
atmospheres and enters the intertubular space of the first evaporator.
The compressor sucks up the steam from the juice of the first evaporator
(which is boiling at the pressure of the atmosphere, without vacuum or
effective pressure), compresses it to 1.4 atmospheres, and forces it
likewise into the intertubular space. The ebullition of the first
evaporator, then, is kept up not only by the exhaust from the motive
cylinder, but also by the steam from the juice itself, which has been
rendered fit to serve as a heating steam by the pressure that it has
undergone in the compressing cylinder.

In this first application of the new system to sugar making, it became
a question of ascertaining whether the advantage resulting from
compression was of great importance, and, in the second place, whether
the apparatus could be run with certainty and ease. In truth, the
applications of the system for some years past in other industries
permitted a favorable result to be hoped for, and the result turned out
as was expected.

With this apparatus it has been found that the work furnished by one
kilogramme of steam passing through the motive cylinder, from a
pressure of 5 atmospheres to one of 1.4, is sufficient to compress 2.5
kilogrammes of steam taken from the juice, led into the compressor
at one atmosphere and escaping therefrom at 1.4. In other words, one
kilogramme of motive steam is sufficient to convert into heating steam
for the first evaporator 2.5 kilogrammes of steam taken from the juice
in this same evaporator. Besides, this same kilogramme of motive steam
produces three effects, one in this same evaporator, and the other
two in the two succeeding ones. The effect obtained, then, from one
kilogramme of motive steam is, in round numbers, 5.5 kilogrammes of
steam removed from the juice.

It must not be forgotten that the motive steam was at the very moderate
pressure of 4 effective atmospheres. Had the use of steam at high
pressure (7 atmospheres for example) been possible, it is easy to
conclude from the above results that more than 6 kilogrammes of water
would have been vaporized with one kilogramme of steam.

The results here cited were ascertained by accurately measuring the
quantities of water of condensation from each evaporator, they soon
received, moreover, the most important of confirmations by the decrease
in the general consumption of fuel by the generators which occurred
after the new apparatus was set in operation.

The mean consumption of coal per 24 hours for the twenty days preceding
the 18th of November was 86,060 kilogrammes. After this date the regular
consumption was as follows:

Nov. 19.................31,800 kilogrammes.
" 20.................33,800 "
" 21.................33,800 "
" 22.................32,000 "
" 23.................31,400 "
" 24.................31,600 "
" 25.................30,500 "
" 26.................30,500 "
" 27.................28,600 "
" 28.................30,300 "

It must be remarked that in the perfectly regular running of the sugar
works, nothing was changed saving the setting of this evaporating
apparatus running. The same quantity of beets was treated per 24 hours,
and the general temperature remained the same. This remarkable result in
the saving of fuel was brought about notwithstanding the new apparatus
treated but a third, at the most, of the total amount of the juice, the
rest continuing to be concentrated by the double action process.

As for the running of the apparatus, that was perfectly regular, and the
deviations in temperature in each evaporater were scarcely two or three
degrees. The following are the mean temperatures:

First evaporator: heating steam 110 deg. C.; juice steam 100 deg. C. Second
evaporator: juice steam 83 deg. C. Third evaporator: juice steam 62 deg. C. As
regards facility of operating the apparatus, the experiment has proved
so conclusive that the plant will be considerably enlarged in view of
the coming crop, in order that a larger quantity of juice may be treated
by the new process. The effect of this will be to still further increase
the saving in coal that has already been effected by the present
apparatus. The engraving which accompanies this article represents the
Weibel-Piccard apparatus as it is now working in the Pohrlitz sugar
works. What we have said of it above we think will suffice to make it
understood without further explanation.--_Le Genie Civil_.

* * * * *

COMPARISON OF STRENGTH OF LARGE AND SMALL ANIMALS.

W. N. LOCKINGTON.

M. Delebeuf, in a paper read before the Academie Royale de Belgique, and
published in the _Revue Scientique_, reviews the attempts of various
naturalists to make comparisons between the strength of large animals
and that of small ones, especially insects, and shows that ignorance or
forgetfulness of physical laws vitiates all their conclusions.

After a plea for the idea without which the fact is barren, M. Delbeuf
repeats certain statements with which readers of modern zoological
science are tolerably familiar, such as the following: A flea can jump
two hundred times its length; therefore a horse, were its strength
proportioned to its weight, could leap the Rocky Mountains, and a whale
could spring two hundred leagues in height. An Amazon ant walks about
eight feet per minute, but if the progress of a human Amazon were
proportioned to her larger size, she could stride over eight leagues in
an hour; and if proportioned to her greater weight, she would make the
circuit of the globe in about twelve minutes. This seems greatly to the
advantage of the insect. What weak creatures vertebrates must be, is the
impression conveyed.

But the work increases as the weight. In springing, walking, swimming,
or any other activity, the force employed has first to overcome the
weight of the body. A man can easily bound a height of two feet, and
he weighs as much as a hundred thousand grasshoppers, while a hundred
thousand grasshoppers could leap no higher than one--say a foot. This
shows that the vertebrate has the advantage. A man represents the volume
of fifteen millions of ants, yet can easily move more than three hundred
feet a minute, a comparison which gives him forty times more power, bulk
for bulk, than the ant possesses. Yet were all the conditions compared,
something like equality would probably be the result. Much of the force
of a moving man is lost from the inequalities of the way. His body,
supported on two points only when at rest, oscillates like a pendulum
from one to the other as he moves. The ant crawls close to the ground,
and has only a small part of the body unsupported at once. This
economizes force at each step, but on the other hand multiplies the
number of steps so greatly, since the smallest irregularity of the
surface is a hill to a crawling creature, that the total loss of force
is perhaps greater, since it has to slightly raise its body a thousand
times or so to clear a space spanned by a man's one step.

By what peculiarity of our minds do we seem to expect the speed of an
animal to be in proportion to its size? We do not expect a caravan to
move faster than a single horseman, nor an eight hundred pound shot to
move twelve thousand eight hundred times farther than an ounce ball.
Devout writers speak of a wise provision of Nature. "If," say they, "the
speed of a mouse were as much less than that of a horse as its body is
smaller, it would take two steps per second, and be caught at once."
Would not Nature have done better for the mouse had she suppressed the
cat? Is it not a fact that small animals often owe their escape to their
want of swiftness, which enables them to change their direction readily?
A man can easily overtake a mouse in a straight run, but the ready
change of direction baffles him.

M. Plateau has experimented on the strength of insects, and the facts
are unassailable. He has harnessed carabi, necrophori, June-beetles
(Melolontha), and other insects in such a way that, with a delicate
balance, he can measure their powers of draught. He announces the result
that the smallest insects are the strongest proportioned to their size,
but that all are enormously strong when compared bulk, for bulk, with
vertebrates. A horse can scarcely lift two-thirds of its own weight,
while one small species of June-beetle can lift sixty-six times its
weight; forty thousand such June-beetles could lift as much as a
draught-horse. Were our strength in proportion to this, we could play
with weights equal to ten times that of a horse.

This seems, again, great kindness in Nature to the smaller animal. But
all these calculations leave out the elementary mechanical law: "What
is gained in power is lost in time." The elevation of a ton to a given
height represents an expenditure of an equal amount of force, whether
the labor is performed by flea, man, or horse. Time supplies lack of
strength. We can move as much as a horse by taking more time, and can
choose two methods--either to divide the load or use a lever or a
pulley. If a horse moves half its own weight three feet in a second,
while a June-beetle needs a hundred seconds to convey fifty times
its weight an equal distance, the two animals perform equal work
proportioned to their weights. True, the cockchafer can hold fourteen
times its weight in equilibrium (one small June-beetle sixty-six times),
while a horse cannot balance nearly his own weight. But this does not
measure the amount of oscillatory motion induced by the respective
pulls. For this, both should operate against a spring.

A small beetle can escape from under a piece of cardboard a hundred
times its weight. Pushing its head under the edge and using it as a
lever, it straightens itself on its legs and moves the board just a
little, but enough to escape. Of course, we know a horse would be
powerless to escape from a load a hundred times its own weight. His head
cannot be made into a lever. Give him a lever that will make the time he
takes equal to that taken by the insect, and he will throw off the load
at a touch. The fact is that in small creatures the lack of muscular
energy is replaced by time.

Of two muscles equal in bulk and energy the shortest moves most weight.
If a muscular fiber ten inches in length can move a given weight five
inches, ten fibers one inch long will move ten times that weight a
distance of half an inch. Thus smaller muscles have an absolutely
slower motion, but move a greater proportional weight than larger.
The experimenter before mentioned was surprised to find that two
grasshoppers, one of which was three times the bulk of the other,
leaped an equal height. This was what might be expected of two animals
similarly constructed. The spring was proportioned to the bulk. In
experiments on the insects with powerful wings, such as bees, flies,
dragon-flies, etc., it was found that the weight they could bear without
being forced to descend was in most cases equal to their own. In some
cases it was more, but the inequality of rate of flight, had it been
taken into the reckoning, would have accounted for this.

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