HEAT VACUUMS
IN THE preceding chapter we dealt with high temperatures and their
employment in melting, molding, and working steel into useful forms. It
will be well for us to pause here to consider temperatures at the other
end of the thermometer scale, how they are obtained, and the important
part they play in modern civilization.
It is not absolutely correct to speak of producing “cold.” We are apt
to forget that cold is merely absence of heat. Strictly speaking, there
is nothing cold on earth. Everything is more or less hot. A piece of
ice at 32 degrees F. is hot compared with a lump of frozen alcohol, and
the latter at its freezing point is hot compared with a lump of frozen
air, while air at its freezing point is hot compared with a lump of
solid helium. In other words, frozen alcohol will be melted by the heat
in the ice; frozen air will be melted by the heat in frozen alcohol,
and frozen helium will be fused by the heat in frozen air. Everything
contains heat, and one object is colder than another only because it
contains less heat.
Of course, the temperature of ice may vary. One block of ice may be
ten, fifty, or a hundred degrees warmer than another, but ice cannot be
heated above 32 degrees F. at the normal pressure of the atmosphere.
Ice is really a partial heat vacuum, a chamber partially exhausted,
into which heat will flow if it gets a chance. We pack it away in
sawdust, granulated cork, or other materials through which heat can
with difficulty penetrate, and then in hot weather cakes of ice are
placed in our household refrigerators, so that the heat that is in our
food will have something to flow into. When we place our hands near a
cake of ice, they feel cool and it seems as if ice radiated cold just
as a stove radiates heat; but, of course, such is not the case. The
heat of our hands radiates more rapidly in the direction of the cake of
ice than in other directions, because there is a partial heat vacuum
for the heat to flow into and the result is a sensation of cold.
We no longer depend upon cold winters for our supply of ice. We have
learned how to pump heat and we can make heat vacuums, anywhere and
at any time, even in the heart of the tropics, and regions in which
no natural ice is ever obtainable have the benefits of refrigeration.
Furthermore, we are not dependent upon ice for cooling foods. In many
cases it is not necessary or even desirable to reduce temperatures
to the freezing point of water. A moderate chilling is all that
is required for certain foods. By the proper use of refrigerating
machinery any degree of temperature may be obtained and maintained.
To-day small refrigerating plants are constructed for domestic
purposes, so as to render the housewife independent of the ice man.
With refrigerator cars and refrigerating plants on shipboard,
fruit from the far west and from tropical lands may be brought to
our breakfast table. Meats from northern slaughterhouses may be
transported in perfect condition into hot southern climes. There
are also certain industries which are dependent on the use of the
low temperatures. In breweries, dairies, margarine factories, etc.,
refrigeration is of the utmost importance, and refrigerating machinery
is used for cooling and drying the air blast for blast furnaces.
In some few places refrigerating machinery is used to cool buildings
in warm weather and make life more bearable in summer weather. It is
highly probable that refrigeration of dwellings will be more and more
extensively developed. In winter time we can make the climate in our
houses anything we please. Why should we not control the indoor climate
in summer time as well?
ABSOLUTE ZERO
The volume of a gas varies inversely in accordance with the pressure to
which it is subjected, and also directly according to the temperature.
If we start with a gas at the freezing point (32 degrees F.) and reduce
its temperature 1 degree (or to 31 degrees F.), we find that the volume
of the gas is reduced 1/492.6 of its original volume, provided, of
course, that we do not vary the pressure on it. In fact, for every
reduction of 1 degree below the freezing point there is a reduction of
1/492.6 of its volume, and for every degree of increased temperature
there is an increase of 1/492.6 of the volume. From this it is assumed
that at 492.6 degrees below the freezing point, or 460.6 degrees below
zero F., we will reach the absolute zero, or the point at which there
is no more heat in the gas.
We have not yet succeeded in reaching the extreme of low temperature,
although we have come very near it in laboratory experiments. Helium
is liquefied at -448 degrees F., which is very near to the absolute
zero. At the other end of the scale we have attained enormously
high temperatures. The heat of the electric arc, for instance, is
between 6,500 and 7,200 degrees F., and that is the highest degree of
temperature that we have been able so far to attain.
Human life occupies a very limited zone in this range of temperatures.
We must maintain our blood at a temperature of 98 degrees F. A
variation of 8 degrees either way is fatal. By piling on heat
insulators, such as fur clothing, to retain the heat of our bodies
and keep it from flowing out too rapidly, we can maintain the blood
temperature at 98 while the surrounding atmosphere may be 70 or 80
degrees below zero. There are internal fires within us that generate
heat which radiates from the body, and by checking this radiation by
suitable clothing we can maintain our blood at the normal temperature.
But what can we do when the surrounding temperature is higher than
blood heat? The outside heat may be kept from flowing in by surrounding
ourselves with heat-insulating clothing, but the internal heat then
has no means of radiating away from our bodies; it accumulates, and
we become overheated. However, Nature provides a cooling system in
the perspiration which oozes from our pores, and as this evaporates
it cools the skin and enables us to maintain our normal blood heat,
although submerged in an atmosphere of a higher temperature. If the air
is dry, the evaporation is more rapid and the cooling is greater than
in a moist atmosphere. That is why a temperature of 105 degrees on our
Western plains may be more endurable than a temperature of 95 degrees
in the moist atmosphere of New York. The importance of keeping down the
temperature of the blood is particularly appreciated by physicians, and
for this reason the earliest attempts at artificial cooling were made
by physicians.
EARLY USES OF LOW TEMPERATURES
Very early in his history man discovered fire, learned how to kindle it
and how to use it for his good. That discovery placed him immediately
on a level far above the beasts. However, it is only in comparatively
recent times that he has learned the uses of low temperatures. Nature’s
stores of ice were drawn upon, and methods of preserving ice through
warm weather were discovered in ancient times. Nero had ice houses
built for him in Rome, but he could stock these buildings only with the
ice that nature furnished him. Freezing mixtures of salt and ice, such
as we use in our ice-cream freezers to-day to obtain temperatures far
below the freezing point of water, were probably known in early times,
but the ancients did not know how to produce ice.
Artificial ice was probably first made in India, where it has long
been the practice to produce ice by evaporation. Water is placed in
shallow pans and then dry air is circulated over it, causing so rapid
a vaporization as to cool the water to the freezing point. The idea
of cooling water by evaporation belongs to very ancient times. Water
placed in porous earthen vessels was found to be cooler than water
kept in water-tight jars. The moisture that escaped through the vessel
would evaporate, and in so doing draw heat out of the vessel and its
contents. To-day campers keep water cool by putting it in canvas
buckets and hanging the buckets in the wind, so that the moisture
oozing through the canvas will evaporate quickly.
It was not until 1755 that a mechanical means of producing low
temperatures was developed. The inventor was Dr. Cullen, and he used an
evaporation system, expediting the evaporation by producing a partial
vacuum over the water. But nearly a century elapsed before the first
commercially successful refrigerating machine was built. Even then the
advantages of artificial refrigeration were not fully realized, and it
was not until late in the last century that real progress was made.
Since then the development of artificial refrigeration has been truly
remarkable.
HEAT AND MECHANICAL ENERGY
There is a definite relation between heat and mechanical energy, in
fact the two are mutually convertible. The amount of heat required
to raise the temperature of a pound of water 1 degree F. is called
a British thermal unit or a B. t. u. This measure is taken at 39.1
degrees F., because at that temperature water is at its densest. Since
heat and mechanical energy are mutually convertible, we can express
foot-pounds or horsepower in B. t. u. One B. t. u. is equivalent to
778 foot-pounds of energy. In other words, the amount of heat that
would raise the temperature of a pound of water 1 degree F. would, if
converted into mechanical energy, be sufficient to raise a weight of
778 pounds to a height of one foot, or one pound to a height of 778
feet. A horsepower is equivalent to 2,545 B. t. u. per hour.
Heat from burning coal is used to generate steam, and this in turn
is used to operate a steam engine and thus heat is converted into
mechanical energy (unfortunately most of the original heat units in the
coal are wasted, as was pointed out in a previous chapter); but heat
will not flow from one body into another of higher temperature without
the expenditure of mechanical energy. It always flows from a hot body
into a cold one, and not from the cold body into the hot one, unless
it is actually pumped up to the higher heat level by some mechanical
means. A refrigerating machine is actually a heat pump with which we
produce a partial heat vacuum.
Whenever a gas is compressed, heat is generated. Anyone who has
operated a tire pump knows how hot the pump becomes from the heat
that is seemingly squeezed out of the compressed air. As was noted in
Chapter VIII, heat is liable to give trouble in an air compressor,
and sometimes the temperature rises to such a point that there is
an explosion of the air and the vapors coming from the oil used to
lubricate the machine. The compressed air is therefore cooled by means
of water jackets or coils of pipe through which water is passed.
In this way the excess heat is carried off. When, however, cooled
compressed air is relieved of pressure and allowed to expand again
the process is reversed. A partial heat vacuum is formed and heat
from surrounding objects flows into the vacuum. In other words, the
surrounding objects are cooled.
COLD AIR MACHINES
[Illustration: FIG. 79.--COLD AIR MACHINE]
It is a simple matter to make a machine which will alternately
compress, cool, and expand air in such a way as to produce a lowered
temperature. Such a machine is indicated diagrammatically in Figure
79. There are two cylinders, _A_ and _B_, and a condenser at _C_. When
the piston _a_ in cylinder _A_ descends it compresses the air in the
cylinder; this air flows into the condenser _C_. There is a coil of
pipe in this condenser through which water circulates. This carries off
the heat of compression and then a valve is opened which permits the
cooler air to pass off into cylinder _B_. As the air expands in this
cylinder it becomes chilled. This chilled air is then forced out of
cylinder _B_ by means of piston _b_ and flows into the refrigerator or
cold storage room _D_. As the air is liable to take up moisture and to
introduce objectionable vapors from oil used to lubricate the pumps, it
is usually confined in pipes in the refrigerator and then returned to
the cylinder _A_.
[Illustration: COMPOSITOR AT WORK ON A LINOTYPE MACHINE]
[Illustration: THE OPTOPHONE
An instrument which enables the blind to read common print]
[Illustration: A BLIND MAN READING WITH HIS EARS]
This is a type of a refrigerating machine that is used very extensively
on ships for chilling perishable foods. However, air has only a very
low capacity for heat, and in order to obtain an appreciable amount of
refrigeration very large volumes of air must be handled. This means
that cold-air machines must be very large and bulky. The efficiency of
such machines is low, but they find favor on shipboard because there
are no inflammable or poisonous gases to be dealt with. In the standard
machine of the United States Navy air is compressed to 260 pounds; and
in the expansion is raised to 60 pounds pressure, which is enough to
reduce the temperature to between 70 to 90 degrees below zero.
LATENT HEAT
Far more efficient are the machines which utilize latent heat. As
explained in a previous chapter, whenever a solid is converted into a
liquid or into a gas a certain amount of heat is absorbed and stored
up in such a way as not to become apparent to the senses or to a
thermometer. Such heat is known as “latent heat.” For instance, we can
add a pound of water at 50 degrees temperature to a pound of water at
200 degrees, and the mixture will have a temperature of 125 degrees, or
the mean of 200 + 50 degrees. But a pound of ice at 32 degrees mixed
with a pound of water at 200 degrees will not give us 116 degrees
((200+32)/2), but only 44½ degrees. In other words, about 143 heat
units will be rendered latent in converting solid water into liquid
water, reducing the temperature of the water to 57 degrees and then
the mean of 57 and 32 is 44.5 (200-143=57, (57+32)/2 = 44½). A more
striking experiment is to mix a pound of water cooled to 32 degrees F.
with a pound of water at 175 degrees F., and the result will be two
pounds of water at 103.5 degrees, but if we mix a pound of chopped ice
at 32 degrees F. with a pound of water at 175 degrees F., the result
will be two pounds of water cooled to the freezing point.
In passing from a liquid into a gas water absorbs far more heat and
renders it latent. For each pound of water converted into steam at
atmospheric pressure 970 B. t. u. are absorbed. This storage of latent
heat is utilized to good advantage in refrigerating machinery. The
vacuum machine invented by Dr. Cullen in 1755 was a latent heat machine.
VACUUM MACHINES
As we have observed before, the boiling point of a liquid depends upon
the pressure to which it is subjected. Under the normal atmospheric
pressure of 14.7 pounds per inch the boiling point of water is 212
degrees F., but if the pressure be increased the boiling point rises,
and if it be reduced the boiling point is lowered. In a partial vacuum
of ten pounds absolute pressure the boiling point is 193.2 degrees, at
one pound it is 102.1 degrees, and if the pressure is reduced to .089
pound water will boil at 32 degrees, or its normal freezing point. Dr.
Cullen, by exhausting the air from a vessel containing water, made the
water boil or vaporize at a low temperature. In order to boil it had
to absorb heat, and not being supplied with any external heat it had
to draw upon itself, thus producing ice.
[Illustration: FIG. 80.--DIAGRAMMATIC VIEW OF A VACUUM REFRIGERATING
MACHINE]
Dr. Cullen’s machine has been improved upon by using various chemical
substances to absorb the water vapor. Such a machine is shown in Figure
80. The vacuum chamber _A_ is partly filled with brine, which may be
cooled below the freezing point of pure water without congealing. A
pump, _B_, maintains a vacuum in the chamber. In the upper part of
the vacuum chamber there is a vessel, _C_, into which sulphuric acid
is sprayed from a reservoir, _D_. This acid has a strong affinity for
water vapor and hastens the evaporation by absorbing the vapor with
which it comes in contact. The mixed sulphuric acid and water flows
over into a receiver, _E_. The acid is reconcentrated by steam heat so
that it can be used over again. However, this feature of the process is
not shown in the diagram. Brine from the chamber _A_ passes through
a coil of pipe _F_ in the tank _G_, where the ice is made, and it is
returned to the vacuum chamber by an injector _H_, which at the same
time introduces fresh water into the chamber to take the place of that
absorbed by the acid. The fresh water and brine enter as a spray at
_I_, so as to increase the rate of evaporation.
[Illustration: FIG. 81.--ORIGINAL ABSORPTION MACHINE]
THE ABSORPTION PROCESS
Another form of refrigeration is known as the absorption system,
and strangely enough direct heat is applied to the machine in one
place in order to abstract heat from it in another. A diagrammatic
representation of the first machine of this type (which was invented
by Frederick Carré) is shown in Figure 81. Two vessels, _A_ and _B_,
are employed, which are connected by a tube _C_. The vessel _A_
contains ammonia solution. A lamp, _D_, is placed under the vessel _A_.
Sufficient heat is produced to vaporize the ammonia, whose boiling
point is very low, and distill it out of the water in the solution. It
passes through tube _C_ into vessel _B_. This vessel is surrounded by
a tank, _E_, containing cold water, which condenses the ammonia vapor
into liquid ammonia, then the process is reversed.
The circulation of water through tank _E_ is checked and water from
pipe _F_ is sprayed on vessel _A_. This cools the contents of vessel
_A_, producing a partial vacuum. The ammonia in chamber _B_ boils and
its vapors pass back into chamber _A_, where they are reabsorbed by the
water in that chamber. The rapid vaporization in chamber _B_ absorbs
heat from the immediate surroundings and will freeze water placed in
the tank _E_.
In commercial practice the absorption system is very extensively
employed. The ammonia is placed in a large cylinder known as a
generator and is heated by steam coils. The ammonia vapor passes
through an analyzer which traps any water vapor it may contain, and
then it goes through a series of condensing coils, which are cooled by
water. In these condensing coils the ammonia vapor is liquefied by the
pressure in the generator and collects in a receiver, whence it passes
through an expansion valve into the cooling coils in the brine tank.
From the cooling coils the ammonia gas passes back through an absorber
which reverses the operation of the generator. Here weak aqua ammonia
is sprayed on the ammonia gas and absorbs it. The rich ammonia solution
is then pumped into the generator.
There are several auxiliary apparatus which are omitted in this brief
description in the interest of clarity.
THE COMPRESSION SYSTEM
[Illustration: FIG. 82.--DIAGRAMMATIC VIEW OF A COMPRESSION MACHINE]
One more type of refrigerating machine remains to be described and
that is the compression type. This was invented by Jacob Perkins in
1834, but was not developed into a commercial machine until 1850.
This machine is the most important of them all. In some respects it
is like the absorption process, but in place of adding direct heat
a compressing machine is employed. Figure 82 illustrates the system
diagrammatically. At _A_ is the compressor which compresses ammonia
gas. The gas which is heated by the compressor is then cooled and
liquefied in the condenser _B_. Thence it passes into a brine tank _C_,
where it expands and absorbs heat. From this point it is drawn back
into the compressor, thus completing the cycle. In other words, the
ammonia must absorb as much heat from the brine as is taken out of it
at the condenser.
CHAPTER XXIII
ENGINES OF DESTRUCTION
AT THE VERY beginning of this book we observed that war is a most
potent stimulus to invention among primitive men. Despite all our
advances in civilization we still have our wars, each more dreadful
than the preceding one; for each important conflict brings forth new
engines of destruction or stimulates the invention of new death-dealing
machines which are developed during intervals of peace. So terrible
has modern war become that with each great conflict it has seemed as
if its very dreadfulness would stay the hand of the invader and make
him hesitate to expose his men to the horrible monsters which science
and invention have created. To-day, after a titanic struggle which cost
millions of human lives, which destroyed billions of dollars’ worth of
property, and which made itself felt to the remotest corners of the
earth, serious efforts are being made to banish war, but at the same
time inventors here and abroad are busy inventing new and more powerful
engines of death, and the prospects are that the next big war, should
there ever be one, will be even more horrible and destructive than the
one we have just passed through.
Fortunately engines of death are not the only inventions produced
by war. Many machines, apparatus, and processes are originated or
developed which have a distinct value in time of peace; hence war is a
great constructive as well as a destructive agency. In this respect the
great World War was no exception and we are already reaping benefits
which in a small way compensate for the havoc that was wrought. It
advanced scientific research to a point it would not have reached in
fifty years of peace. The stimulus was felt in every field of science
from chemistry to acoustics, from geology to meteorology. Wonderful
progress was made in radiotelephony, in submarine navigation, in
aviation, and there were scores of inventions which will add to our
comfort and aid us in the mastery of Nature.
Many of these inventions have already been described; others do
not properly belong in this volume as they have to do chiefly with
electricity or chemistry. In this chapter we shall take up mainly the
machines built for the purpose of destroying men and their works.
PRIMITIVE “ENGINES” OF WAR
Of course the main objects of war are offense and defense, the
destruction of the opponent and the protection of one’s self. This
first fighting was a hand-to-hand struggle which gave way to fighting
at a distance as spears and arrows were invented. Shields and armor
were then invented to ward off these missiles. Cities were surrounded
with walls to hold off the enemy. Then came the Roman war “engines,”
catapults and battering rams, to destroy the walls and towers which
would enable the besiegers to fight on an equal level and in personal
contact with the besieged. Although a battle might start with
long-distance fighting it was always a hand-to-hand encounter that
clinched the victory. Even to-day, although we have our big guns which
fight at ranges of five to twenty miles, it is the rifle or bayonet
which wins or loses the battle.
INVENTION OF GUNPOWDER
The introduction of gunpowder from China in the fifteenth century did
not immediately revolutionize warfare. It was used only in cannon or
mortars for hurling large stones at city walls. The range of those
cannon was so limited and the time it took to load and fire them was so
great that they were of little use on an open battlefield. A cannon,
although a comparatively powerful offensive weapon, was helpless
against attack and was only suitable for use in forts or behind
breastworks. Later when its range was increased and it came to be used
on the battlefield it had to be protected from capture by men supplied
with small arms.
This defect of the cannon also applied to the use of the hand gun. Its
range was small and consequently the blunderbuss type was invented to
spread the charge of shot as much as possible so as to tear a wide gap
in the enemy’s line and prevent it from closing in upon the operator
of the gun. But the loading and firing of these early firearms was
extremely slow and the battle-ax and even the arrow and the crossbow
were much more effective weapons. So unreliable were the muskets of our
Revolutionary War that in battle more dependence was placed upon the
bayonet than the firearm.
THE SPINNING BULLET
Three important improvements were necessary to make the small gun a
really effective weapon. First was the invention of a reliable means
of igniting the powder; second the rifling of the barrel so that the
bullet would not tumble but would hold a true course, and finally
the invention of a cartridge and a rifle that could be loaded from
the breech. These improvements were not completely effected until
the time of the Civil War. Since then there have been further marked
improvements: The power of cartridges has been increased; the bullets
have been given a stream-line form so as to increase the range of the
rifle and its power of penetration; the rifle has been equipped with a
magazine for carrying a number of cartridges; and a simple mechanism
has been provided for discharging empty shells and inserting fresh
cartridges in a minimum of time.
Gyroscopic action plays a very important part in the flight of a
bullet or shell. The spiral grooves cut in the bore of the rifle give
the projectile a twist that sets it to spinning rapidly. The spinning
bullet is virtually a gyroscope and maintains its axis in the line
of flight. Hence it is possible to use a long pointed bullet instead
of the round ball of earlier days and to give the projectile a shape
that will enable it to cut through the air with comparatively little
resistance. The same bullet fired from a smooth bore gun would begin to
tumble and would encounter so much air resistance that it would fall
short in the space of a few hundred feet, besides which it would wander
far off its course.
MACHINE GUNS
A rifle is really a machine for hurling small projectiles. During the
Civil War a Chicago physician named Gatling fell to pondering over the
inefficiency of using a machine that would fire only one bullet at a
time with a considerable interval of time between shots for reloading,
and he hit upon the idea of developing a machine that would discharge
a continuous stream of bullets. So he built a ten-barrel revolving gun
operated by a hand crank. The barrels were automatically loaded and
fired one after the other. Although it was slow to accept the Gatling
machine gun, the U. S. Army after once accepting it was loath to give
it up even after better machine guns were invented.
UTILIZING THE KICK OF A GUN
In the Gatling gun hand power was required to operate the loading,
firing and shell-ejecting mechanism, but it occurred to another
inventor that a small portion of the energy developed in exploding the
cartridge could very well be utilized to replace the hand power and
thus make the machine gun completely automatic. It was Hiram Maxim who
first carried out this idea to a successful conclusion. When a rifle
is fired the suddenly expanding gases push back against the breech of
the gun with just as much pressure as they do against the bullet and
this shows itself in the recoil or “kick” of the gun. Maxim utilized
the kick of the gun to cock the gun, open the breech, eject the empty
shell, take a fresh cartridge out of a magazine belt, insert it in the
breech chamber, lock the breech and fire the gun. All these operations
occupied but an instant of time and the gun kept on firing as long as
the belt of cartridges held out.
John M. Browning, inventor of the Colt gun, instead of using the
recoil, employed a small portion of the gases to operate the mechanism.
A minute hole in the barrel of the gun, near the muzzle, communicated
with a small cylinder in which was a spring-pressed piston. The gases
pursuing the bullet out of the barrel would find this tiny hole and,
entering it, push back the piston. The pressure against the piston
would be only a small fraction of that exerted against the bullet and
would last for only the briefest part of a second, from the time the
bullet uncovered the hole to the time it emerged from the barrel and
liberated the gases, but this minute portion of the energy of the
powder was sufficient to actuate the mechanism which performed all the
operations necessary to reload and fire the gun.
COOLING THE GUN BARREL
The advantage of these machine guns over Gatling’s lay not only in
the saving of human labor, but in the fact that a single barrel was
employed in place of ten, thereby greatly reducing the weight of the
gun. But a serious handicap was encountered in the heat developed
by the burning powder. Dr. Gatling, by using ten barrels, could let
nine be cooling while the tenth was discharging, but even he found it
necessary to place a water jacket about half the length of the barrels.
In the Maxim machine gun a large water jacket enveloped the whole
length of the barrel and when the gun was firing continuously at a
moderate rate the 7½ pints of water contained in the water jacket would
come to a boil inside of a minute and a half, and thereafter more than
a pint would be evaporated each minute of firing, or about a pint and
a half per thousand rounds. The necessity of using water-cooling added
considerably to the weight of the gun and made it occupy in the service
an intermediate place between the shoulder rifle and the big gun.
Another method of cooling was to use a barrel with a large outer
diameter and depend upon the radiation of heat from the outer surface
to prevent overheating. This was later improved by putting flanges
on the outer surface of the barrel, so as to increase the radiating
surface, in the same way that the cylinders of a motorcycle are kept
cool. The barrel was made easily detachable and a spare one provided,
so that as soon as the barrel grew excessively hot it could be removed
and replaced with a cool barrel. The fault of overheating is not that
it might explode the cartridge prematurely but that the bore will
be enlarged by heat expansion so that the bullets will not take the
rifling and will come out of the barrel as if from a smooth-bore gun.
In a test of a Hotchkiss machine gun which was fired continuously
the expansion was sufficient at the end of four minutes to make the
course of the bullets very uncertain and in seven minutes the bullets,
emerging without any spin, tumbled over and over and failed to carry
more than three hundred yards.
A GUN THAT FANS ITSELF
The next marked step in the development of the machine gun was to
make it fan itself and thus keep its barrel cool. Col. I. N. Lewis
designed a gun operated by gas pressure somewhat on the principle of
the Colt gun and around the barrel he fitted sixteen deep flanges or
fins of aluminum that ran lengthwise of the gun. Around these fins
he fitted a casing, thus forming 16 long narrow chambers about the
barrel. The casing was open at the breech end, but at the outer end was
contracted into a narrow mouthpiece that extended beyond the muzzle.
The mouthpiece was so formed that as the bullets passed through it
they sucked air through the chambers, thereby cooling the gun. The air
travels through the casing at the rate of about seventy miles per hour.
This design permitted Col. Lewis to build a very light gun. Its total
weight was but 25½ pounds and it could be handled by a single man
if the muzzle was supported on some sort of a rest. It represented
a marked step toward a shoulder machine gun which would increase
enormously the efficiency of infantry equipped with this weapon. The
difference between rifle fire and machine-gun fire has been likened to
the difference between trying to hit a tin can with a stone and with a
stream of water from a hose. In the latter case the hose may be raised
or lowered to correct the course of the stream and bring it to bear on
the target. In the same way by watching the effect of the machine-gun
bullets the leaden stream may be corrected to bring it directly upon
the target. The advantages of a weapon such as this, which may be fired
from the shoulder or from the hip, are perfectly obvious.
As the war was nearing its end John M. Browning produced two machine
guns, one a water-cooled heavy model fired from a stand. The total
weight of this gun was 34½ pounds and with the water jacket empty it
weighed but 22½ pounds. It was operated by the recoil of the gun, but
the mechanism was greatly simplified and there were but few parts.
These could be taken apart and replaced with new ones in a minimum of
time in case of breakage. The other gun was a shoulder rifle weighing
only 16 pounds, which carried a clip of twenty cartridges. These could
be fired singly or in rapid succession in the space of two and a half
seconds. Only a second was required to replace the empty clip with a
filled one. No special cooling apparatus was provided because it was
not likely that a shoulder rifle would be fired long enough at a time
to become excessively heated.
POCKET-SIZED MACHINE GUN
The latest development in machine guns is a pocket edition weapon--a
firearm weighing only 7 pounds and measuring but 22 inches over all.
This little gun which is too small to be classed as a rifle and yet
rather large for a pistol, has two grips so that it may be fired from
the waist line, and it may be fitted with a gun butt so that it may be
fired from the shoulder. It operates at the astounding rate of 1,500
shots per minute or three times the speed of the average machine gun.
The cartridges are fed either from a box magazine containing 20 rounds
or from a drum-shaped magazine loaded with 50 to 100 cartridges. The
operating mechanism of this gun is entirely different from anything
produced heretofore and depends upon a discovery made by Commander
Blish of the United States Navy. He found that a wedge of a certain
angle will hold a breechblock closed against the pressure of an
exploding cartridge while the pressure is high, but will slide when
the pressure falls. Apparently at first the adhesion due to friction
is too great to permit the wedge to move, but the adhesion falls off
more rapidly than the pressure does and a point is reached at which
the wedge yields to the pressure. In the “submachine” gun, as the new
weapon is called, the barrel (or rather an extension of the barrel)
and the receiver, in which the operating mechanism is contained, are
locked together by a wedge. The wedge slides in slots set at an angle
of 80 degrees with the axis of the barrel. When a cartridge is fired
the wedge remains fast while the bullet is traveling through the bore,
but when it emerges and the pressure of the gases falls off the wedge
slides, unlocking the breech mechanism. The gun is remarkable for its
simplicity and the fewness of its parts. It has been adopted by the
Police Department of New York City.
ARTILLERY VS. ARMOR
As has been stated above, gunpowder was first introduced in warfare
not for the purpose of destroying men, but for smashing city walls and
fortifications, so that infantry could pour through the breeches made
by the heavy stone or iron projectiles. As artillery grew more powerful
and the aim more accurate walls of masonry gave way to earthworks
and to masses of concrete and armored steel. However the World War
demonstrated the impossibility of building any fortifications above
ground that would stand up against modern high-powered guns.
GUNS, MORTARS, AND HOWITZERS
In military parlance a “gun” is a long-barreled piece that fires
its projectiles with a flat trajectory, that is, the projectile is
fired at a low angle and describes a long flat curve. A “mortar” is
a short-ranged weapon which fires at a high angle so as to land its
projectile over the walls of a fortification. The barrel of the mortar
was formerly very short and had a smooth bore, but later the barrel was
extended and the bore rifled so as to give a greater range, developing
what is known as the “howitzer.” The famous 42-centimeter gun with
which the Germans started the war was a howitzer which fired a shell a
yard and a half long weighing 2,108 pounds. We have big guns to defend
our coasts which fire a shell 16 inches in diameter, which is half an
inch less than 42 centimeters, and the weight of the shell is 2,400
pounds. But the startling thing about the German big howitzers was that
they were portable and could be brought up to smash fixed defenses.
As the war proceeded enormous guns as well as howitzers were set on
railroad mounts and moved about from time to time to avoid discovery by
spying aviators.
THE 76-MILE GUN
The 76-mile gun which bombarded Paris fired projectiles of only
8.27-inch caliber. The projectile described a wide curve which carried
it about twenty-four miles above the surface of the earth or about
3½ times as high as the greatest altitude ever reached by man in an
aeroplane. Had it pursued a perfectly straight line from the forest
of St. Gobain to Paris its course would have carried it 3,750 feet
below the surface, because of the curvature of the earth. The range
of the projectile was very materially increased by rising to such a
great elevation because of the extreme tenuity of the atmosphere.
The air resistance that a shell is obliged to overcome is not
generally appreciated. In the denser strata of the lower atmosphere
the resistance is very great, but as a shell mounts to higher levels
the air resistance falls off considerably and at twenty miles it is
practically nonexistent.
It was not until the summer after the armistice that details of this
gun were disclosed. There were seven of these powerful guns that
participated in the various bombardments. They wore out very quickly
under the terrific strain to which they were subjected and were rebored
to a diameter of 9.4 inches. In the last bombardment a number of
shells of this size reached Paris. The guns were fired at an angle
of 55 degrees from the horizontal so as to pass quickly through the
denser layers of the air. The shell left the muzzle of the gun with
the velocity of about 5,000 feet per second and arrived in Paris about
three minutes later with a velocity of about half that amount. The
enormous muzzle velocity was obtained by using a very long gun so that
the powder could keep pushing the projectile for a comparatively long
time. The guns were built out of worn-out 15-inch naval guns. These
guns which were 56 feet long were rebored, fitted with a heavy tube and
pieced out to a length of 118 feet. The last 20 feet of the bore was
not rifled and served as a guide to keep the shell in perfect axial
alignment when it emerged from the muzzle. A comparatively slow powder
was used so as not to put too severe a strain on the gun at the breech,
but gradually to accelerate the shell in its travel through the bore.
Spectacular as was the performance of these huge guns, they were of
little military value. The slightest variation in the powder would
cause a wide variation of range and they could not hope to hit a target
smaller than a large city. All seven guns fired a total of 303 shells
in 44 days of bombardment, only 183 of which fell within the city. They
killed 256 persons and wounded 620. Far more damage at far less expense
could have been effected by dropping bombs from aircraft.
A 121-MILE GUN
Just as a problem in ordnance, American officers designed a gun 225
feet long which would fire a 400-pound shell of 10-inch caliber. It
was estimated that with a charge of 1,440 pounds of powder the shell
would leave the muzzle with a velocity of 8,500 feet per second and,
if fired at an angle of 55 degrees, would have a range of 121 miles.
The shell would rise to a height of 46 miles above the earth and would
make the 121 miles in about 4 minutes. The gun was never built, because
its military value would in no way be commensurate with its cost of
construction and operation. The purpose of the German long-range
bombardment was to produce a moral rather than a military effect. The
Germans hoped to intimidate the French people by this spectacular
performance, and in this they failed completely.
TIMED AND PERCUSSION SHELLS
In modern warfare large guns are used either to rain a storm of death
upon infantry or to destroy their defensive works. In earlier days the
effectiveness of gunfire against a charging enemy was increased by the
use of grapeshot. A cannon was thus converted into a gigantic shotgun.
But although a wide dispersion of projectiles was obtained the range
was very limited. This handicap was then overcome by having the gun
fire another gun which would discharge when it had reached the enemy’s
lines. In other words, the grapeshot or leaden balls were packed into
a shell which was fired like a solid projectile, and this exploded
when it struck the target, scattering death broadcast. An improvement
on this was the timed shell, which would explode while still in the
air and scatter its rain of lead over a wide area. The time fuse of
a shrapnel shell must be very delicately adjusted to explode at the
desired instant. A train of powder is used which may be short-circuited
to give the exact length required for any given distance. The powder
is ignited by a cap which is exploded by concussion when the gun is
fired. The fuse then burns until it reaches the main charge of the
shell. This explodes, bursting the shell open and scattering shell
fragments as well as the scores of lead balls with which the shell is
packed. Should the fuse fail, a detonating pin is provided which will
explode the shell when it reaches the ground. Where the object is to
destroy defensive works the shell is charged with a high explosive
which is detonated not by a time fuse, but by concussion when the shell
strikes its target.
The war brought forth many new types of projectiles: shells loaded with
lethal gases; shells which left a trail of smoke whereby their course
could be followed when fired at aircraft; shells that illuminated the
battlefield at night, etc. The searchlight shells carried a number of
“candles,” each furnished with a little parachute so that when the
shell exploded the burning candles would settle slowly to the ground,
all the while casting a brilliant light on operations below.
AERIAL BOMBS
Obviously, hurling projectiles from the air is a much simpler matter
than projecting them from the ground. No propellant is required to
carry them to the target and no rifling is necessary to keep them
head-on in the direction of flight. They are pulled instead of being
pushed and can easily be kept in their course by means of rudder
planes. But hitting a target from an aeroplane is like hitting a
swiftly moving object from the ground. The target is seemingly flying
past the aeroplane and in calculating where the aerial bomb will strike
the speed of the plane through the air and its height above the ground
must all be taken into consideration.
Naval warfare is a fight of fort against fort and consequently the high
explosive projectile is the principal one used. The shells must be
able to penetrate heavy steel armor and explode within the hull of the
vessel. In addition to these we have the torpedoes fired by destroyers
and submarines which explode an enormous quantity of high explosive
against the hull of the vessel. No attempt is made to penetrate the
skin of the vessel, but the explosive, tamped by a considerable depth
of water, delivers a very heavy crushing blow against the side of the
hull.
AUTOMATIC CONTROL OF SUBMARINE TORPEDOES
It is wrong to speak of firing a torpedo. A torpedo is really an
automatic, self-propelled, submarine boat. All that the destroyer or
submarine does is to set the steering gear in this little boat and then
launch it at the enemy with a blast of air that ejects it from the
torpedo tube. Most of the body of the torpedo is filled with compressed
air which drives a small air motor coupled to a pair of propellers.
These propellers run in opposite directions so as to balance each other
and they drive the torpedo through the water at a speed of about forty
miles per hour. The speed falls off gradually as the air supply is
exhausted.
To hold the torpedo on its course horizontal and vertical rudders are
employed. The vertical rudder is controlled by a gyroscope which turns
it this way or that according as the torpedo tends to veer off its
course.
The value of a torpedo lies in its concealment. Were it to travel on
the surface the vessel against which it was directed might be able to
avoid it; furthermore the action of the waves would tend to disturb
the gyroscopic steering mechanism and the torpedo would pursue an
erratic course. For this reason it must travel under water at a depth
sufficient to avoid surface disturbances. There is also a distinct
advantage in having a good cover of water over the torpedo when it
strikes its target because the force of the explosion, although felt
in all directions, is mainly expended along the line of the least
resistance. If the depth of water over the torpedo is slight, most of
the force will be expended upward and only a comparatively small part
will act against the hull of the vessel. It was the practice of the
Germans to set their torpedoes for a depth of about ten feet.
To hold a torpedo at a fixed depth a very delicate hydrostatic valve
is employed which operates the diving rudders. The valve is set for a
certain depth or weight of water. If the torpedo goes below this depth,
the weight of the water bearing on this valve presses it down and
thereby tilts the diving rudders until the torpedo comes back to the
required depth. If it rises above the depth for which it is set, the
valve feels the reduction of water pressure and tilts the rudders in
the opposite direction to correct the deviation from the predetermined
line of travel. Once the valve has been set the torpedo takes care of
itself automatically. It may be discharged from any depth or be dropped
from torpedo tubes on the deck of a ship and after a few undulations it
will find its depth and hold it as long as it keeps running.
Torpedoes have actually been discharged from aeroplanes and it is
possible that in the next great war swiftly flying aeroplanes may
actually bring death and destruction to powerful dreadnoughts. In fact
winged destroyers and battle cruisers of the air may render obsolete
all our modern fighting machines.
As we have already observed, it was war that first aroused the
inventive instincts in man. Fortunately this instinct was not confined
to destructive devices and engines, and the mechanical conquest of the
earth, although it continues to derive much benefit from the stimulus
of war, may well afford to break off relations with so grim and
horrible a partner and proceed to develop under the stimulus of its own
successes.
CHAPTER XXIV
SUMMARY OF MECHANICAL PROGRESS
THE REAL beginning of the present age of machinery dates from Watt’s
invention of the double-acting steam engine which was patented in 1782.
Prior to that date the steam engine was used merely for pumping water,
but now in its new form it was adapted for use in driving industrial
machinery. But, as we have shown in another chapter, it was not until
John Wilkinson invented his boring machine in 1774 that it was possible
to bore the cylinders that Watt used in his engine.
In the field of machine tools there were several notable inventions.
Henry Maudslay invented the slide rest for lathes and later in 1797
the screwcutting lathe. Joseph Bramah invented the hydraulic press and
Maudslay furnished the cup leather packing that made it a success.
Woodworking machinery, and particularly mortising machines for making
pulley blocks, were invented by Samuel Bentham and patented in 1791 and
1793.
In the textile industry we find the spinning jenny invented by
Hargreaves in 1770, Richard Arkwright’s roll-drawing spinning machine
invented in 1769 and 1775, and Crompton’s mule spinner invented between
1774 and 1779, but never patented. In addition to this there was the
invention of the cotton gin in 1794 by our own Eli Whitney and Dr.
Cartwright’s series of patents on the power-driven loom granted
between 1785 and 1788. In 1799 Louis Roberts invented a machine that
would make a continuous web of paper. The machine was developed in
England by the Fourdrinier Brothers and has ever since borne their name.
1801-1810
Just before the Nineteenth Century dawned the patents on Watt’s steam
engine expired and the invention became public property.
Trevithic applied steam power to the propulsion of a coach in 1801.
This was the forerunner of the automobile and it led to the invention
of the first steam railway and locomotive three years later. Steam was
also applied to the propulsion of boats in this decade and reached
the practical stage when Fulton built the Clermont in 1807. The first
application of steam to the driving of a loom is accredited to William
Horrocks in 1803. Jacquard’s loom attachment for producing various
patterns was invented in 1801. The first knitting machine in which the
latch needle was used was patented in France in 1806 by Jeandeau.
Among the machine-tool developments the most important were Bramah’s
invention of the planer in 1802 and Brunel’s mortising machine in 1801.
A process of making malleable iron castings was invented by Lucas in
1804. The percussion lock for guns was invented by Forsyth in 1807.
1811-1820
The second decade saw a much wider application of steam and
considerable development in locomotives. Hedley’s “Puffing Billy” was
built in 1813, and Stephenson’s first locomotive in 1814.
In the same year Fulton built the first steam war vessel and five years
later the Atlantic was crossed for the first time by a steamer, the
Savannah. The rotary steam printing press belongs to this decade.
The circular knitting machine was invented by Brunel in 1816. About
1818 Eli Whitney invented the milling machine, and in 1819 Blanchard
invented his “gun-stocking” lathe with which irregular forms could be
turned out. The breech-loading musket was patented in this country by
Thornton and Hall in 1811.
1821-1830
In this decade we find the conversion of electricity into mechanical
motion and many other important electrical developments, which,
however, are omitted from this list as we are confining ourselves
to mechanical inventions. There were marked developments in steam
railroads. Stephenson built the “Rocket” which won prizes on the
Liverpool and Manchester Railway, and the first locomotive was imported
into this country in 1829. The tubular locomotive boiler was invented
by Seguin in 1828 and Ericsson’s portable steam fire engine was built
in 1830. In the previous year an important improvement in spinning
mules was made when John Thorpe invented the ring frame.
1831-1840
Important railroad developments mark the opening of this decade. The
famous locomotive “John Bull” was imported from England in 1831 to
operate on the Camden and Amboy Railroad. The following year saw the
first American-built locomotive, “Old Ironsides,” which was built
at Philadelphia by the Baldwin Locomotive Works. Stephenson’s link
motion, also claimed by W. T. James, was invented in 1832.
However, the most important development of the decade was the invention
of the reaper. Hussey’s patent was obtained in 1833 and McCormick’s the
following year.
Colt’s revolver (1836); Perkin’s portable ice machine (1834); Anthony’s
(1831), Tolle’s (1834), and Burden’s (1835) developments in machines
for making horseshoes; and Isaac Babbit’s antifriction-bearing metal
are other notable developments.
1841-1850
It was in 1841 that F. E. Sickels invented the drop cut-off valve gear,
and the Corliss valve gear was patented in 1849 and 1851. Nasmyth’s
steam hammer was invented in 1842.
Hoe’s revolving printing press was invented in 1845. The next year
Sloan patented the gimlet-pointed screw. In 1847 Savage invented the
time lock, and in 1849 Hibbert patented the latch needle for knitting
machines. American machine-made watches appeared in 1850. However, the
most important invention of the decade was Howe’s sewing machine in
1845.
1851-1860
The year 1851 saw an important improvement in the harvester when
Seymour invented his self-raker, also an advance in firearms when
Maynard invented the breech-loading rifle. Three years later Smith &
Wesson came forth with their magazine rifle which was the forerunner of
the “Winchester.” In that year Wilson invented the four-motion feed for
sewing machines.
One of the most notable inventions of the decade was Bessemer’s
converter for producing steel (1855), and the following year Siemens
produced the regenerative furnace.
Gifford’s injector (1858) marked a most important advance in steam
engineering. The hand-turned turret for lathes was invented by Stephen
Fitch about 1853, and the automatically revolving turret was brought
out in 1855.
Other inventions of the decade were Herman’s diamond drill (1854),
Ericsson’s air engine (1855), the pedal-operated bicycle by Ernest
Michaux (1855), use of wood pulp in the manufacture of paper by Voelter
(1858), and the ammonia absorption ice machine invented by Carré.
1861-1870
The Civil War directed attention of inventors to military and naval
improvements. Dr. Gatling invented his machine gun in 1862, the same
year that Ericsson built the “Monitor.” It is interesting to note that
the revolving turret was patented in that year by Theodore R. Timby.
Dynamite was invented in 1867, and the Whitehead torpedo in the same
year. Barbed wire was invented in 1861. The same year saw the first
passenger elevator invented by Otis; the shoe-sewing machine invented
by McKay, and Col. Green’s invention of the drive well, which was
brought about by the necessity of supplying his troops with water.
The pneumatic rock drill was invented by Burleigh in 1866, and
Westinghouse invented the air brake in 1869. The latter, with Sholes’s
invention of the typewriter in the previous year, were undoubtedly the
most notable inventions of the decade.
In 1865 the cylindrical grinder marked a decided forward step in
machine tools.
1871-1880
This decade was marked by great activity, particularly in the field of
electricity. While we are confining ourselves to mechanical inventions
we cannot but mention Bell’s telephone (1876), Edison’s carbon filament
lamp (1878), and Berliner’s transmitter and Edison’s carbon microphone
which belong to the decade, although their patents were not issued
until 1891 and 1892 respectively.
The web printing press was invented by Hoe in 1871. Ingersoll’s
compressed air rock drill appeared in the same year. A marked
improvement in the Westinghouse air brake was patented in 1872, and the
automatic car coupler appeared in 1873. The positive motion loom was
invented by Lyall in 1872.
The harvester was improved by Gorham’s twine binder in 1874, and in the
same year a machine for making barbed wire was produced.
The Centennial year saw an important development in milling processes
when the roller mill was introduced to take the place of the
time-honored millstones. The middlings purifier was invented by George
T. Smith in 1875. The hydraulic dredge was invented in 1876, also the
universal grinder, and a machine for making cigarettes.
Edison’s invention of the phonograph and Otto’s invention of the gas
engine give prominence to the year 1877 and the Remington typewriter to
the year 1878.
1881-1890
The inventions of most far-reaching importance in this decade were
Mergenthaler’s linotype machine, which was invented in 1884 and
further developed into a practical machine in 1890; Gottlieb Daimler’s
invention of the automobile in 1883, and J. B. Dunlop’s invention of
the pneumatic tire in 1890.
Berliner in 1887 invented the flat-disk talking machine known as the
“Gramophone.” The snapshot “Kodak” camera appeared in 1888. In this
year De Laval invented his steam turbine, while Harvey invented his
process for annealing armor plate.
The following year nickel steel was invented. In 1883 Sir Hiram Maxim
invented the machine gun. Hugo Bilgram’s generating system of gear
cutting was invented in 1881.
A less prominent, though very important, invention of the same year was
the buttonhole machine patented by Reece.
Incidentally this decade saw the completion of the Brooklyn Suspension
Bridge in 1883, and the Great Forth Bridge in 1890.
1891-1900
The last decade of the Nineteenth Century gave us Parson’s steam
turbine (1891) and Curtis’s steam turbine (1896); also Rudolf Diesel’s
heavy-oil engine.
Langley’s model for a motor-driven airplane was built in 1896 and
actually flew. Santos-Dumont made his first ascension in a dirigible in
1898, and Count Friedrich von Zeppelin built his first rigid dirigible
in 1900.
J. B. Holland built a steam-driven submarine, and Simon Lake
constructed the first submarine to be driven by an internal combustion
engine.
This decade was largely devoted to the development of the automobile,
which gradually evolved into a truly commercial machine. About 1900,
Benjamin Holt invented the “caterpillar” tractor. The decade also
saw the invention of the Lanston “monotype,” and Henry Wise Wood’s
“autoplate” machine which revolutionized stereotyping.
In 1899 William Draper brought out a loom with an automatic
shuttle-changing mechanism. Hulett invented the automatic ore unloader
in 1898. Improvements were also made in automatic machine tools. J. E.
Gleason improved the Bilgram gear cutter in 1898, and at the close of
the century Taylor and White brought out their high-speed cutting tools
which revolutionized machine tools.
The decade was also remarkable for the invention of X-rays, wireless
telegraphy, and certain chemical processes, none of which really belong
in this summary.
1901-1910
In this decade the automobile reached a marvelous state of perfection
and a tremendous industry was built up which had a marked influence
on the development of machine tools and the production of iron
and steel. James A. Gailey invented a dryblast process for steel
production, getting rid of the moisture in air by subjecting it to
a freezing process. Fellow’s gear-cutting machine was perfected and
Bullard brought out the vertical turret lathe. There were important
developments of the steam turbine.
There is one invention that makes this decade stand out from among all
others. On December 17, 1903, the Wright brothers made a successful
flight in a biplane driven by a gasoline engine, and opened up a new
world for conquest. Man took to wings and the dream of ages was
realized. During the decade rapid progress was made in developing the
flying machine. The invention of the monoplane soon followed.
It was in this decade that the gyroscope emerged from the laboratory
and toy shop and began to be applied to practical uses. Schlick
utilized the gyroscope to prevent ships from rolling. The gyrocompass
was invented and reached a commercial stage in 1910.
1911-1920
It is difficult to pick out the most important inventions of this
decade because sufficient time has not elapsed to determine which are
most deserving of mention. The Great World War stimulated invention in
all civilized lands. Aeronautics developed faster in the five years of
war than it could in twenty-five years of peace. Of course, engines of
war developed to a remarkable degree. Among the lighter pieces we saw
the development of the Lewis gun, and then the Browning gun. The most
important invention was the tank. Many advances should be classed as
remarkable developments rather than basically new inventions. The war
of and against the submarine brought forth many ingenious devices.
Of the peace-time inventions, the most remarkable is the optophone, the
instrument which enables the blind to read ordinary printed matter.
* * * * *
And thus the march of progress continues unchecked. We are tempted to
give our imaginations free play and forecast the developments that the
future holds in store for us, but unfortunately we cannot claim any
prophetic instinct or inspiration.
TRANSCRIBER’S NOTE:
--Obvious print and punctuation errors were corrected.