PNEUMATICS AND PNEUMATIC MACHINES.
“The march of the human mind is slow,” exclaimed Burke in his great
speech on “Conciliation with the Colonies.” It was at the beginning of
the last quarter of the 18th century that he was speaking, and he was
referring to the slow discovery of the eternal laws of Providence as
applied in the field of political administration to distant colonies.
The same could then have been said of the march of the human mind in the
realms of Nature. How slow had been the apprehension of the forces of
that kind but silent Mother whose strong arms are ever ready to lift and
carry the burdens of men whenever her aid is diligently sought! The
voice of Burke was, however, hardly silent when the human mind suddenly
awoke, and its march in the realms of government and of natural science
since then cannot be regarded as slow.
More than fifteen centuries before Burke spoke, not only had Greece
discovered the principles of political freedom for its citizens and its
colonies, but the power of steam had been discovered, and experimental
work been done with it.
Yet when the famous orator made his speech the Grecian experiment was a
toy of Kings, and the steam engine had just developed from this toy into
a mighty engine in the hands of Watt. The age of mechanical inventions
had just commenced with the production of machines for spinning and
weaving. And yet, in view of the rise of learning, and the appearance
from time to time of mighty intellects in the highest walks of science,
the growth of the mind in the line of useful machinery had indeed been
strangely slow. “Learning” had revived in Italy in the 12th and 13th
centuries and spread westward in the 14th. In the 15th, gunpowder and
printing had been discovered, and Scaliger, the famous scholar of Italy,
and Erasmus, the celebrated Dutch philosopher, were the leading
restorers of ancient literature. Science then also revived, and
Copernicus, the Pole, gave us the true theory of the solar system. The
16th century produced the great mathematicians and astronomers Tycho
Brahe, the Dane, Cardan and Galileo, the illustrious Italians, and
Kepler, the German astronomer, whose discovery of the laws of planetary
motion supplemented the works of Copernicus and Galileo and illuminated
the early years of the 17th century.
In the 17th century appeared Torricelli, the inventor of the barometer;
Guericke, the German, inventor of the air pump; Fahrenheit, the inventor
of the mercurial thermometer bearing his name; Leibnitz, eminent in
every department of science and philosophy; Huygens, the great Dutch
astronomer and philosopher; Pascal of France and Sir Isaac Newton of
England, the worthy successors of Kepler, Galileo and Copernicus; and
yet, with the exception of philosophical discoveries and a few
experiments, the field of invention in the way of motor engines still
remained practically closed. But slight as had been the discoveries and
experiments referred to, they were the mine from which the inventions of
subsequent times were quarried.
One of the earliest, if not the first of pneumatic machines, was the
bellows. Its invention followed the discovery of fire and of metals. The
bladders of animals suggested it, and their skins were substituted for
the bladders.
The Egyptians have left a record of its use, thirty-four centuries ago,
and its use has been continuous ever since.
Mention has been made of the cannon. It was probably the earliest
attempt to obtain motive power from heat. The ball was driven out of an
iron cylinder by the inflammatory power of powder. Let a piston be
substituted for the cannon ball, as was suggested by Huygens in 1680 and
by Papin in 1690, and the charge of powder so reduced that when it is
exploded the piston will not be thrown entirely out of the cylinder,
another small explosive charge introduced on the other side of the
piston to force it back, or let the cylinder be vertical and the piston
be driven back by gravity, means provided to permit the escape of the
gas after it has done its work, and means to keep the cylinder cool, and
we have the prototype of the modern heat engines. The gunpowder
experiments of Huygens and Papin were not successful, but they were the
progenitors of similar inventions made two centuries thereafter.
Jan Baptista van Helmont, a Flemish physician (1577-1644), was the first
to apply the term, _gas_ to the elastic fluids which resemble air in
physical properties. Robert Boyle, the celebrated Irish scholar and
scientist, and improver of the air pump, and Edwin Mariotte, the French
physicist who was first to show that a feather and a coin will drop the
same distance at the same time in a reservoir exhausted of air, were the
independent discoverers of Boyle’s and Mariotte’s law of
gases(1650-1676). This was that at any given temperature of a gas which
is at rest its volume varies inversely with the pressure put upon it. It
follows from this law that the density and tension, and therefore the
expansive force of a gas, are proportional to the compressing force to
which it is subjected. It is said that Abbé Hauteville, the son of a
baker of Orleans, about 1678 proposed to raise water by a powder motor;
and that in 1682 he described a machine based on the principle of the
circulation of the blood, produced by the alternate expansion and
contraction of the heart.
The production of heat by concentrating the rays of the sun, and for
burning objects had been known from the time of Archimedes, and been
repeated from time to time.
Thus stood this art at the close of the 17th century, and thus it
remained until near the close of the 18th.
In England Murdock, the Cornish Steam Engineer, was the first to make
and use coal gas for illuminating purposes, which he did in 1792 and
1798. Its utilisation for other practical purposes was then suggested.
Gas engines as motive powers were first described in the English patent
to John Barber, in 1791, and then in one issued to Robert Street in
1794. Barber proposed to introduce a stream of carbonated hydrogen gas
through one port, and a quantity of air at another, and explode them
against the piston. Street proposed to drive up the piston by the
expansive force of a heated gas, and anticipated many modern ideas.
Phillipe Lebon, a French engineer, in 1799 and in 1801 anticipated in a
theoretical way many ideas since successfully reduced to practice. He
proposed to use coal gas to drive a piston, which in turn should move
the shaft that worked the pumps which forced in the gas and air, and
thus make the machine double-acting; to introduce a charge of
inflammable gas mixed with sufficient air to ignite it; to compress the
air and gas before they entered the motor cylinder; to introduce the
charge alternately on each side of the piston; and he also suggested the
use of the electric spark to fire the mixture. But Lebon was
assassinated and did not live to work out his ideas.
At the very beginning of the 19th century John Dalton in England,
1801-1807, and Gay-Lussac in France began their investigations of gases
and vapours. Dalton was not only the author of the atomic theory, but
the discoverer of the leading ideas in the “Constitution of Mixed
Gases.” These features were the diffusion of gases, the action of gases
on each other in vacuum--the influence of different temperatures upon
them, their chemical constituents and their relative specific gravity.
Gay-Lussac, continuing his investigations as to expansion of air and
gases under increased temperatures, in 1807-10, established the law that
when free from moisture they all dilate uniformly and to equal amounts
for all equal increments of temperature. He also showed that the gases
combine, as to volume, in simple proportions, and that several of them
on being compounded contracted always in such simple proportions as
one-half, one-third, or one-quarter, of their joint bulk. By these laws
all forms of engines which were made to work through the agency of heat
are classed as heat engines--so that under this head are included steam
engines, air engines, gas engines, vapour engines and solar engines. The
tie that binds these engines into one great family is temperature. It is
the heat that does the work. Whether it is a cannon, the power of which
is manifested in a flash, or the slower moving steam engine, whose
throbbing heart beats not until water is turned to steam, or the sun,
the parent of them all, whose rays are grasped and used direct, the
question in all cases is, what is the amount of heat produced and how
can it be controlled?
It, then, can make no difference what the agent is that is employed,
whether air, or gas, or steam, or the sun, or gunpowder explosion, but
what is the temperature to be attained in the cylinder or vessel in
which they work. Power is the measure of work done in a given time.
Horse power is the unit of such measurement, and it consists of the
amount of power that is required to raise one pound through a vertical
distance of one foot. This power is pressure and the pressure is heat.
The unit of heat is the amount of heat required to raise the temperature
of a pound of distilled water one degree--from 39 degrees to 40 degrees
F. Its amount or measurement is determined in any instance by a
dynamometer.
These were the discoveries with which Philosophy opened the nineteenth
century so brilliantly in the field of Pneumatics.
Before that time it seemed impossible that explosive gases would ever be
harnessed as steam had been and made to do continual successful work in
a cylinder and behind a piston. As yet means were to be found to make
the engine efficient as a double-acting one--to start the untamed steed
at the proper moment and to stop him at the moment he had done his work.
As Newcomen had been the first in the previous century to apply the
steam engine to practical work--pumping water from mines--so Samuel
Brown of England was the first in this century to invent and use a gas
engine upon the water.
Brown took out patents in 1823 and 1826. He proposed to use gunpowder
gas as the motive power. His engine was also described in the
_Mechanics’ Magazine_ published in London at that time. In the making of
his engine he followed the idea of a steam engine, but used the flame of
an ignited gas jet to create a vacuum within the cylinder instead of
steam. He fitted up an experimental boat with such an engine, and means
upon the boat to generate the gas. The boat was then operated upon the
Thames. He also succeeded experimentally in adapting his engine to a
road carriage. But Brown’s machines were cumbrous, complicated, and
difficult to work, and therefore did not come into public use.
About this time (1823), Davy and Faraday reawakened interest in gas
engines by their discovery that a number of gases could be reduced to a
liquid state, some by great pressure, and others by cold, and that upon
the release of the pressure the gases would return to their original
volume. In the condensation heat was developed, and in re-expansion it
was rendered latent.
Then Wright in 1833 obtained a patent in which he expounded and
illustrated the principles of expansion and compression of gas and air,
performed in separate cylinders, the production of a vacuum by the
explosion and the use of a water jacket around the cylinder for cooling
it.
For William Burdett, in 1838, is claimed the honour of having been the
first to invent the means of compressing the gas and air previous to the
explosion, substantially the same as adopted in gas engines of the
present day.
The defects found in gas engines thus far were want of proper
preliminary compression, then in complete expansion, and finally loss of
heat through the walls.
Some years later, Lenoir, a Frenchman, invented a gas engine of a
successful type, of which three hundred in 1862 were in use in France.
It showed what could be accomplished by an engine in which the fuel was
introduced and fired directly in the piston cylinder. Its essential
features were a cylinder into which a mixture of gas and air was
admitted at atmospheric pressure, which was maintained until the piston
made half its stroke, when the gas was exploded by an electric spark. A
wheel of great weight was hung upon a shaft which was connected to the
piston, and which weight absorbed the force suddenly developed by the
explosion, and so moderated the speed. Another object of the use of the
heavy wheel was to carry the machine over the one-half of the period in
which the driving power was absent.
Hugon, another eminent French engineer, invented and constructed a gas
engine on the same principle as Lenair’s.
About this time (1850-60) M. Beau de Rohes, a French engineer,
thoroughly investigated the reasons of the uneconomical working of gas
motors, and found that it was due to want of sufficient compression of
the gas and air previous to explosion, incomplete expansion and loss of
heat through the walls of the cylinder, and he was the first to
formulate a “cycle” of operations necessary to be followed in order to
render a gas engine efficient. They related to the size and dimensions
of the cylinder; the maximum speed of the piston; the greatest possible
expansion, and the highest pressure obtainable at the beginning of the
act of expansion. The study and application of these conditions created
great advancements in gas engines.
With the discovery and development of the oil wells in the United States
about 1860 a new fuel was found in the crude petroleum, as well as a
source of light. The application of petroleum to engines, either to
produce furnace heat, or as introduced directly into the piston cylinder
mixed with inflammable gas to produce flame heat and expansion, has
given a wonderful impetus to the utilisation of gas engines.
G. H. Brayton of the United States in 1873 invented a very efficient
engine in which the vapour of petroleum mixed with air constituted the
fuel. Adolf Spiel of Berlin has also recently invented a petroleum
engine.
Principal among those to whom the world is indebted for the revolution
in the construction of gas engines and its establishment as a successful
rival to the steam engine is Nicolaus A. Otto of Deutz on the Rhine.
In the Lenair and Hugon system the expansive force of the exploded gas
was used directly upon the piston, and through this upon the other
moving parts. A great noise was produced by these constant explosions.
In the Otto system the explosion is used indirectly and only to produce
a vacuum below the piston, when atmospheric pressure is used to give the
return stroke of the piston and produce the effective work. The Otto
engine is noiseless. This is accomplished by his method of mixing and
admitting the gases. He employs two different mixtures, one a “feebly
explosive mixture,” and the other “a strongly explosive mixture,” used
to operate on the piston and thus prolong the explosions.
The mode of operation of one of Otto’s most successful engines is as
follows: The large fly wheel is started by hand or other means, and as
the piston moves forward it draws into the cylinder a light charge of
mixed coal gas and air, and the gas inlet is then cut off. As the piston
returns it compresses this mixture. At the moment the down stroke is
completed the compressed mixture is ignited, and, expanding, drives the
piston before it. In the second return stroke the burnt gases are
expelled from the cylinder and the whole made ready to start afresh.
Work is actually done in the piston only during one-quarter of the time
it is in motion. The fly-wheel carries forward the work at the outset
and the gearing the rest of the time.
Otto was associated with Langen in producing his first machine, and its
introduction at the Centennial Exposition at Philadelphia in 1876
excited great attention. Otto and E. W. and W. J. Crossley jointly, and
then Otto singly, subsequently patented notable improvements.
Simon Bischof and Clark, Hurd and Clayton in England; Daimler of Deutz
on the Rhine, Riker and Wiegand of the United States, and others, have
made improvements in the Otto system.
Ammoniacal gas engines have been successfully invented. _Aqua ammonia_
is placed in a generator in which it is heated. The heat separates the
ammonia gas from the water, and the gas is then used to operate a
suitable engine. The exhaust gas is cooled, passed into the previously
weakened solution, reabsorbed and returned to the generator. In 1890
Charles Tellier of France patented an ammoniacal engine, also means for
utilising solar heat and exhaust steam for the same purpose; and in the
same year De Susini, also of France, patented an engine operated by the
vapour of ether; A. Nobel, another Frenchman, in 1894, patented a
machine for propelling torpedoes and other explosive missiles, and for
controlling the course of balloons, the motive power of which is a gas
developed in a closed reservoir by the chemical reaction of metallic
sodium or potassium in a solution of ammonia. These vapour engines are
used for vapour launches, bicycles and automobiles.
In 1851 the ideas of Huygens and Papin of two hundred years before were
revived by W. M. Storm, who in that year took out a gunpowder engine
patent in the United States, in which the air was compressed by the
explosions of small charges of gunpowder. About fifteen other patents
have been taken out in America since that time for such engines. In some
the engines are fed by cartridges which are exploded by pulling a
trigger.
As to gas and vapor engines generally, it may now be said, in comparison
with steam, that although the steam engine is now regarded as almost
perfect in operation, and that it can be started and stopped and
otherwise controlled quietly, smoothly, instantaneously, and in the most
uniform and satisfactory manner, yet there is the comparatively long
delay in generating the steam in the boiler, and the loss of heat and
power as it is conducted in pipes to the working cylinder, resulting in
the utilisation of only ten per cent of the actual power generated,
whereas gas and vapour engines utilise twenty-five per cent of the power
generated, and the flame and explosions are now as easily and
noiselessly controlled as the flow of oil or water. The world is coming
to agree with Prof. Fleeming Jenkins that “Gas engines will ultimately
supplant the steam.”
The smoke and cinder nuisance with them has been solved.
The sister invention of the gas engine is the air engine. There can be
no doubt about the success of this busy body, as it is now a swift and
successful motor in a thousand different fields. Machines in which air,
either hot or cold, is used in place of steam as the moving power to
drive a piston, or to be driven by a piston, are known generally as air,
caloric, or hot-air engines, air compressors, or compressed air engines,
and are also classed as pneumatic machines, air brakes, or pumps. They
are now specifically known by the name of the purpose to which they are
applied, as air ship, ventilator, air brake, fan blower, air pistol, air
spring, etc.
The attention of inventors was directed towards compressed and heated
air as a motor as soon as steam became a known and efficient servant;
but the most important and the only successful air machine existing
prior to this century was the air pump, invented by Guericke in 1650,
and subsequently perfected by Robert Boyle and others. The original pump
and the Magdeburg hemispheres are still preserved.
It is recorded that Amontons of France, in 1699, had an atmospheric fire
wheel or air engine in which a heated column of air was made to drive a
wheel.
It has already been noted what Papin (1680-1690) proposed and did in
steam. His last published work was a Latin essay upon a new system for
raising water by the action of fire, published in 1707.
The action of confined and compressed steam and gases, and air, is so
nearly the same in the machines in which they constitute the motive
power that the history, development, construction, and operation of the
machines of one class are closely interwoven with those of the others.
Taking advantage of what had been taught them by Watt and others as to
steam and steam engines, and of the principles and laws of gases as
expounded by Boyle, Mariotte, Dalton, and Gay-Lussac, that many of the
gases, such as air, preserve a permanent expansive gaseous form under
all degrees of temperature and compression to which they had as yet been
subjected, that when compressed and released they will expand, and exert
a pressure in the contrary direction until the gas and outside
atmospheric pressure are in equilibrium, that this compressed gas
pressure is equal, and transmitted equally in all directions, and that
the weight of a column of air resting on every horizontal square inch at
the sea level is very nearly 14.6 pounds, the inventors of the
nineteenth century were enabled by this supreme illumination to enter
with confidence into that work of mechanical contrivances which has
rendered the age so marvellous.
It was natural that in the first development of mechanical appliances
they should be devoted to those pursuits in which men had the greatest
practical interest. Thus as to steam it was first applied to the raising
of water from mines and then to road vehicles. And so in 1800 Thos.
Parkinson of England invented and patented an “hydrostatic engine or
machine for the purpose of drawing beer or any other liquid out of a
cellar or vault in a public house, which is likewise intended to be
applied for raising water out of mines, ships or wells.” By the use of a
sort of an air pump he maintained an air pressure on the beer in an
air-tight cask situated in the cellar, which was connected with pipes
having air-tight valves, with the upper floor. The liquid was forced
from the cellar by the air pressure, and when turned off, the air
pressure was resumed in the cask, which “preserved the beer from being
thrown into a state of flatness.” Substantially the same device in
principle has been reinvented and incorporated in patents numerous times
since.
In the innumerable applications of the pneumatic machines and air tools
of the century, especially of air-compressing devices, to the daily uses
of life, we may, by turning first to our home, find its inner and outer
walls painted by a pneumatic paint-spraying machine, for such have been
made that will coat forty-six thousand square feet of surface in six
hours; and it is said that paint can be thus applied not only more
quickly, but more thoroughly and durably than by the old process. The
periodical and fascinating practice of house cleaning is now greatly
facilitated by an air brush having a pipe with a thin wide end in which
are numerous perforations, and through which the air is forced by a
little pump, and with which apparatus a far more efficient cleaning
effect upon carpets, mattresses, curtains, clothes, and furniture can be
obtained than by the time-honoured broom and duster.
Is the home uncomfortable by reason of heat and summer insects? A
compressor having tanks or cisterns in the cellar filled with cool or
cold air may be set to work to reduce the temperature of the house and
fan the inmates with a refreshing breeze.
Air engines have been invented which can be used to either heat or cool
the air, or do one or the other automatically. The heating when wanted
is by fuel in a furnace forced up by a working cylinder, and the cooling
by the circulation of water around small, thin copper tubes through
which the air passes to the cylinder.
Do the chimes of the distant church bells lead one to the house of
worship? The worshipper goes with the comforting assurance that the
chimes which send forth such sweet harmonies are operated not by
toiling, sweating men at ropes, but by a musician who plays as upon an
organ, and works the keys, valves and stops by the aid of compressed
air, and sometimes by the additional help of electricity.
Mention has already been made of office and other elevators, in which
compressed air is an important factor in operating the same and for
preventing accidents.
If a waterfall is convenient, air is compressed by the body of
descending water, and used to ventilate tunnels, and deep shafts and
mines, or drive the drills or other tools.
The pneumatic mail tube despatch system, by which letters, parcels,
etc., are sent from place to place by the force of atmospheric pressure
in an air-exhausted tube, is a decidedly modern invention, unknown in
use even by those who are still children. Tubes as large as eight inches
in diameter are now in use in which cartridge boxes are placed, each
holding six hundred or more letters, and when the air is exhausted the
cartridge is forced through the tubes to the distance sometimes of three
miles and more in a few minutes.
In travelling by rail the train is now guided in starting or in stopping
on to the right track, which may be one out of forty or fifty, by a
pneumatic switch, the switches for the whole number of tracks being
under the control of a single operator. The fast-moving train is stopped
by an air brake, and the locomotive bell is rung by touching an air
cylinder. The “baggage smashing,” a custom more honoured in the breach
than in the observance, is prevented by a pneumatic baggage arrangement
consisting of an air-containing cylinder, and an arm on which to place
the baggage, and which arm is then quickly raised by the cylinder piston
and is automatically swung around by a cam action carrying the baggage
out of or into the car.
Bridge building has been so facilitated by the use of pneumatic machines
for raising heavy loads of stone and iron, and for riveting and
hammering, and other air tools, aided by the development in the art of
quick transportation, that a firm of bridge builders in America can
build a splendid bridge in Africa within a hundred days after the
contract has been entered upon.
Ship building is hastened by these same air drilling and riveting
machines.
The propelling of cars, road vehicles, boats, balloons, and even ships,
by explosive gases and compressed air is an extensive art in itself, yet
still in its infancy, and will be more fully described in the chapter on
carrying machines.
The realm of Art has received a notable advancement by the use of a
little blow-pipe or atomiser by which the pigments forming the
background on beautiful vases are blown with just that graduated force
desired by the operator to produce the most exquisitely smooth and
blended effects, while the varying colours are made to melt
imperceptibly into one another as delicately as the mingled shade and
coloured sunlight fall on a forest brook.
But to enumerate the industrial arts to which air and other pneumatic
machines have been adapted would be to catalogue them all. Mention is
made of others in chapters in which those special arts are treated.