water-mills make him our slave. Of late years many prophets have
arisen to warn us that we must not be too lavish of our coal; that the
time is not so far distant, reckoning by centuries, when the
coal-seams of the world will be worked out and leave our descendants
destitute of what plays so important a part in modern life. Now,
though waste is unpardonable, and the care for posterity praiseworthy,
there really seems to be no good reason why we should alarm ourselves
about the welfare of the people of the far future. Even if coal fails,
the winds and the rivers will be there, and the huge unharnessed
energy of the tides, and the sun himself is ready to answer appeals
for help, if rightly shaped. He does not demand the prayers of Persian
fire-worshippers, but rather the scientific gathering of his good
gifts.
Place your hand on a roof lying square to the summer sun, and you will
find it too hot for the touch. Concentrate a beam of sunshine through
a small burning-glass. How fierce is the small glowing focal spot that
makes us draw our hands suddenly away! Suppose now a large glass many
feet across bending several square yards of sun rays to a point, and
at that point a boiler. The boiler would develop steam, and the steam
might be led into cylinders and forced to drudge for us.
Do many of us realise the enormous energy of a hot summer’s day? The
heat falling in the tropics on a single square foot of the earth’s
surface has been estimated as the equivalent of one-third of a
horse-power. The force of Niagara itself would on this basis be
matched by the sunshine streaming on to a square mile or so. A
steamship might be propelled by the heat that scorches its decks.
For many centuries inventors have tried to utilise this huge waste
power. We all know how, according to the story, Archimedes burnt up
the Roman ships besieging his native town, Syracuse, by concentrating
on them the sun heat cast from hundreds of mirrors. This story is less
probable than interesting as a proof that the ancients were aware of
the sun’s power. The first genuine solar machine was the work of
Ericsson, the builder of the _Monitor_. He focused sun heat on a
boiler, which gave the equivalent of one horse-power for every hundred
square feet of mirrors employed. This was not what engineers would
call a “high efficiency,” a great deal of heat being wasted, but it
led the way to further improvements.
In America, especially in the dry, arid regions, where fuel is scarce
and the sun shines pitilessly day after day, all the year round,
sun-catchers of various types have been erected and worked
successfully. Dr. William Calver, of Washington, has built in the
barren wastes of Arizona huge frames of mirrors, travelling on
circular rails, so that they may be brought to face the sun at all
hours between sunrise and sunset. Dr. Calver employs no less than 1600
mirrors. As each of these mirrors develops 10-15 degrees of heat it is
obvious, after an appeal to simple arithmetic, that the united efforts
of these reflectors should produce the tremendous temperature
16,000-24,000 degrees, which, expressed comparatively, means the
paltry 90 degrees in the shade beneath which we grow restive
multiplied hundreds of times. Hitherto the greatest known heat had
been that of the arc of the electric lamp, in which the incandescent
particles between pole and pole attain 6000 degrees Fahrenheit.
The combined effect of the burning mirrors is irresistible. They can,
we are told, in a few moments reduce Russian iron to the consistency
of warmed wax, though it mocks the heat of many blast-furnaces. They
will bake bricks twenty times as rapidly as any kiln, and the bricks
produced are not the friable blocks which a mason chips easily with
his trowel, but bodies so hard as to scratch case-hardened steel.
There are at work in California sun-motors of another design. The
reader must imagine a huge conical lamp-shade turned over on to its
smaller end, its inner surface lined with nearly 1800 mirrors 2 feet
long and 3 inches broad, the whole supported on a light iron
framework, and he will have a good idea of the apparatus used on the
Pasadena ostrich farm. The machine is arranged _in meridian_, that is,
at right angles to the path of the sun, which it follows all day long
by the agency of clockwork. In the focus of the mirrors is a boiler,
13 feet 6 inches long, coated with black, heat-absorbing substances.
This boiler holds over 100 gallons of water, and being fed
automatically will raise steam untended all the day through. The steam
is led by pipes to an engine working a pump, capable of delivering
1400 gallons per minute.
The cheapness of the apparatus in proportion to its utility is so
marked that, in regions where sunshine is almost perpetual, the solar
motor will in time become as common as are windmills and factory
chimneys elsewhere. If the heat falling on a few square yards of
mirror lifts nearly 100,000 gallons of water an hour, there is indeed
hope for the Sahara, the Persian Desert, Arabia, Mongolia, Mexico,
Australia. That is to say, if the water under the earth be in these
parts as plentiful as the sunshine above it. The effect of water on
the most unpromising soil is marvellous. Already in Algeria the French
have reclaimed thousands of square miles by scientific irrigation. In
Australia huge artesian wells have made habitable for man and beast
millions of acres that were before desert.
It is only a just retribution that the sun should be harnessed and
compelled to draw water for tracts to which he has so long denied it.
The sun-motor is only just entering on its useful career, and at
present we can but dream of the great effects it may have on future
civilisation. Yet its principle is so simple, so scientific, and so
obvious, that it is easy to imagine it at no far distant date a
dangerous rival to King Coal himself. To quarry coal from the bowels
of the earth and transform it into heat, is to traverse two sides of a
triangle, the third being to use the sunshine of the passing hour.
LIQUID AIR.
Among common phenomena few are more interesting than the changes
undergone by the substance called water. Its usual form is a liquid.
Under the influence of frost it becomes hard as iron, brittle as
glass. At the touch of fire it passes into unsubstantial vapour.
This transformation illustrates the great principle that the form of
every substance in the universe is a question of heat. A metal
transported from the earth to the sun would first melt and then
vaporise; while what we here know only as vapours would in the moon
turn into liquids.
We notice that, as regards bulk, the most striking change is from
liquid to gaseous form. In steam the atoms and molecules of water are
endowed with enormous repulsive vigour. Each atom suddenly shows a
huge distaste for the company of its neighbours, drives them off, and
endeavours to occupy the largest possible amount of private space.
Now, though we are accustomed to see water-atoms thus stirred into an
activity which gives us the giant steam as servant, it has probably
fallen to the lot of but few of us to encounter certain gaseous
substances so utterly deprived of their self-assertiveness as to
collapse into a liquid mass, in which shape they are quite strangers
to us. What gaseous body do we know better than the air we breathe?
and what should we less expect to be reducible to the consistency of
water? Yet science has lately brought prominently into notice that
strange child of pressure and cold, Liquid Air; of which great things
are prophesied, and about which many strange facts may be told.
Very likely our readers have sometimes noticed a porter uncoupling the
air-tube between two railway carriages. He first turns off the tap at
each end of the tube, and then by a twist disconnects a joint in the
centre. At the moment of disconnection what appears to be a small
cloud of steam issues from the joint. This is, however, the result of
cold, not heat, the tube being full of highly-compressed air, which by
its sudden expansion develops cold sufficient to freeze any particles
of moisture in the surrounding air.
Keep this in mind, and also what happens when you inflate your
cycle-tyre. The air-pump grows hotter and hotter as inflation
proceeds: until at last, if of metal, it becomes uncomfortably warm.
The heat is caused by the forcing together of air-molecules, and
inasmuch as all force produces heat, your strength is transformed into
warmth.
In these two operations, compression and expansion, we have the key to
the creation of liquid air--the great power, as some say, of
to-morrow.
[Illustration: _By kind permission of The Liquid Air Co._
_A view of the Liquid Air Co.’s factory at Pimlico. On the left are
the three compressors, squeezing the air at pressures of 90, 500 and
2,200 lbs. to the square inch respectively. On the right is the
reservoir in which the liquid is stored._]
Suppose we take a volume of air and squeeze it into 1/100 of its
original space. The combativeness of the air-atoms is immensely
increased. They pound each other frantically, and become very hot in
the process. Now, by cooling the vessel in which they are, we rob them
of their energy. They become quiet, but they are much closer than
before. Then imagine that all of a sudden we let them loose again. The
life is gone out of them, their heat has departed, and on separating
they shiver grievously. In other words, the heat contained by the
1/100 volume is suddenly compelled to “spread itself thin” over the
whole volume: result--intense cold. And if this air be brought to bear
upon a second vessel filled likewise with compressed air, the cold
will be even more intense, until at last the air-atoms lose all their
strength and collapse into a liquid.
Liquid air is no new thing. Who first made it is uncertain. The credit
has been claimed for several people, among them Olzewski, a Pole, and
Pictet, a Swiss. As a mere laboratory experiment the manufacture of
liquid air in small quantities has been known for twenty years or
more. The earlier process was one of terrific compression alone,
actually forcing the air molecules by sheer strength into such close
contact that their antagonism to one another was temporarily overcome.
So expensive was the process that the first ounce of liquid air is
estimated to have cost over £600!
In order to make liquid air an article of commerce the most important
condition was a wholesale decrease in cost of production. In 1857 C.
W. Siemens took out a patent for making the liquid on what is known as
the regenerative principle, whereby the compressed air is chilled by
expanding a part of it. Professor Dewar--a scientist well known for
his researches in the field of liquid gases--had in 1892 produced
liquid air by a modification of the principle at comparatively small
cost; and other inventors have since then still further reduced the
expense, until at the present day there appears to be a prospect of
liquid air becoming cheap enough to prove a dangerous rival to steam
and electricity.
A company, known as the Liquid Air, Power and Automobile Company, has
established large plants in America and England for the manufacture of
the liquid on a commercial scale. The writer paid a visit to their
depot in Gillingham Street, London, where he was shown the process by
Mr. Hans Knudsen, the inventor of much of the machinery there used.
The reader will doubtless like to learn the “plain, unvarnished truth”
about the creation of this peculiar liquid, and to hear of the freaks
in which it indulges--if indeed those may be called freaks which are
but obedience to the unchanging laws of Nature.
On entering the factory the first thing that strikes the eye and ear
is the monstrous fifty horse-power gas-engine, pounding away with an
energy that shakes the whole building. From its ponderous flywheels
great leather belts pass to the compressors, three in number, by which
the air, drawn from outside the building through special purifiers, is
subjected to an increasing pressure. Three dials on the wall show
exactly what is going on inside the compressors. The first stands at
90 lbs. to the square inch, the second at 500, and the third at 2200,
or rather less than a ton pressure on the area of a penny! The pistons
of the low-pressure compressor is ten inches in diameter, but that of
the high pressure only two inches, or 1/25 of the area, so great is
the resistance to be overcome in the last stage of compression.
Now, if the cycle-pump heats our hands, it will be easily understood
that the temperature of the compressors is very high. They are
water-jacketed like the cylinders of a gas-engine, so that a
circulating stream of cold water may absorb some of the heat. The
compressed air is passed through spiral tubes winding through large
tanks of water which fairly boils from the fierceness of the heat of
compression.
When the air has been sufficiently cooled it is allowed to pass into a
small chamber, expanding as it goes, and from the small into a larger
chamber, where the cold of expansion becomes so acute that the
air-molecules collapse into liquid, which collects in a special
receptacle. Arrangements are made whereby any vapour rising from the
liquid passes through a space outside the expansion chambers, so that
it helps to cool the incoming air and is not wasted.
The liquid-air tank is inside a great wooden case, carefully protected
from the heat of the atmosphere by non-conducting substances. A tap
being turned, a rush of vapour shoots out, soon followed by a clear,
bluish liquid, which is the air we breathe in a fresh guise.
A quantity of it is collected in a saucepan. It simmers at first, and
presently boils like water on a fire. The air-heat is _by comparison_
so great that the liquid cannot resist it, and strives to regain its
former condition.
You may dip your finger into the saucepan--if you withdraw it again
quickly--without hurt. The cushion of air that your finger takes in
with it protects you against harm--for a moment. But if you held it in
the liquid for a couple of seconds you would be minus a digit. Pour a
little over your coat sleeve. It flows harmlessly to the ground, where
it suddenly expands into a cloud of chilly vapour.
Put some in a test tube and cork it up. The cork soon flies out with a
report--the pressure of the boiling air drives it. Now watch the
boiling process. The nitrogen being more volatile--as it boils at a
lower temperature than oxygen--passes off first, leaving the pure,
blue oxygen. The temperature of this liquid is over 312 degrees below
zero (as far below the temperature of the air we breathe as the
temperature of molten lead is above it!). A tumbler of liquid oxygen
dipped into water is soon covered with a coating of ice, which can be
detached from the tumbler and itself used as a cup to hold the liquid.
If a bit of steel wire be now twisted round a lighted match and the
whole dipped into the cup, the steel flares fiercely and fuses into
small pellets; which means that an operation requiring 3000 degrees
Fahrenheit has been accomplished in a liquid 300 degrees below zero!
Liquid air has curious effects upon certain substances. It makes iron
so brittle that a ladle immersed for a few moments may be crushed in
the hands; but, curiously enough, it has a toughening effect on copper
and brass. Meat, eggs, fruit, and all bodies containing water become
hard as steel and as breakable as glass. Mercury is by it congealed to
the consistency of iron; even alcohol, that can brave the utmost
Arctic cold, succumbs to it. The writer was present when some
thermometers, manufactured by Messrs. Negretti and Zambra, were tested
with liquid air. The spirit in the tubes rapidly descended to 250
degrees below zero, then sank slowly, and at about 260 degrees froze
and burst the bulb. The measuring of such extreme temperatures is a
very difficult matter in consequence of the inability of spirit to
withstand them, and special apparatus, registering cold by the
shrinkage of metal, must be used for testing some liquid gases,
notably liquid hydrogen, which is so much colder than liquid air that
it actually freezes it into a solid ice form!
For handling and transporting liquid gases glass receptacles with a
double skin from which all air has been exhausted are employed. The
surrounding vacuum is so perfect an insulator that a “Dewar bulb” full
of liquid air scarcely cools the hand, though the intervening space is
less than an inch. This fact is hard to square with the assertion of
scientific men that our atmosphere extends but a hundred or two miles
from the earth’s surface, and that the recesses of space are a vacuum.
If it were so, how would heat reach us from the sun, ninety-two
millions of miles away?
One use at least for liquid air is sufficiently obvious. As a
refrigerating agent it is unequalled. Bulk for bulk its effect is of
course far greater than that of ice; and it has this advantage over
other freezing compounds, that whereas slow freezing has a destructive
effect upon the tissues of meat and fruit, the instantaneous action of
liquid air has no bad results when the thing frozen is thawed out
again. The Liquid Air Company therefore proposes erecting depôts at
large ports for supplying ships, to preserve the food, cool the cabins
in the tropics, and, we hope, to alleviate some of the horrors of the
stokehold.
Liquid air is already used in medical and surgical science. In surgery
it is substituted for anæsthetics, deadening any part of the body on
which an operation has to be performed. In fever hospitals, too, its
cooling influence will be welcomed; and liquid oxygen takes the places
of compressed oxygen for reviving the flickering flame of life. It
will also prove invaluable for divers and submarine boats.
In combination with oil and charcoal liquid air, under the name of
“oxyliquit,” becomes a powerful blasting agent. Cartridges of paper
filled with the oil and charcoal are provided with a firing primer.
When everything is ready for the blasting the cartridges are dropped
into a vessel full of liquid air, saturated, placed in position, and
exploded. Mr. Knudsen assured the writer that oxyliquit is twice as
powerful as nitro-glycerine, and its cost but one-third of that of the
other explosive. It is also safer to handle, for in case of a misfire
the cartridge becomes harmless in a few minutes, after the liquid air
has evaporated.
But the greatest use will be found for liquid air when it exerts its
force less violently. It is the result of power; its condition is
abnormal; and its return to its ordinary state is accompanied by a
great development of energy. If it be placed in a closed vessel it is
capable of exerting a pressure of 12,000 lbs. to the square inch. Its
return to atmospheric condition may be regulated by exposing it more
or less to the heat of the atmosphere. So long as it remains liquid
it represents so much _stored force_, like the electricity stored in
accumulators. The Liquid Air Company have at their Gillingham Street
depôt a neat little motor car worked by liquid air. A copper
reservoir, carefully protected, is filled with the liquid, which is by
mechanical means squirted into coils, in which it rapidly expands, and
from them passes to the cylinders. A charge of eighteen gallons will
move the car forty miles at an average pace of twelve miles an hour,
without any of the noise, dirt, smell, or vapour inseparable from the
employment of steam or petroleum. The speed of the car is regulated by
the amount of liquid injected into the expansion coils.
We now come to the question of cost--the unromantic balance in which
new discoveries are weighed and many found wanting. The storage of
liquid air is feasible for long periods. (A large vacuum bulb filled
and exposed to the atmosphere had some of the liquid still
unevaporated at the end of twenty-two days.) But will it be too costly
for ordinary practical purposes now served by steam and electricity?
The managers of the Liquid Air Company, while deprecating extravagant
prophecies about the future of their commodity, are nevertheless
confident that it has “come to stay.” With the small 50 horse-power
plant its production costs upwards of one shilling a gallon, but with
much larger plant of 1000 horse-power they calculate that the expenses
will be covered and a profit left if they retail it at but one penny
the gallon. This great reduction in cost arises from the economising
of “waste energy.” In the first place the power of expansion previous
to the liquefaction of the compressed air will be utilised to work
motors. Secondly, the heat of the cooling tanks will be turned to
account, and even the “exhaust” of a motor would be cold enough for
ordinary refrigerating. It is, of course, impossible to get more out
of a thing than has been put into it; and liquid air will therefore
not develop even as much power as was required to form it. But its
handiness and cleanliness strongly recommend it for many purposes, as
we have seen; and as soon as it is turned out in large quantities new
uses will be found for it. Perhaps the day will come when liquid-air
motors will replace the petrol car, and in every village we shall see
hung out the sign, “Liquid air sold here.” As the French say, “_Qui
vivra verra_.”
HORSELESS CARRIAGES.
A body of enterprising Manchester merchants, in the year 1754, put on
the road a “flying coach,” which, according to their special
advertisement, would, “however incredible it may appear, actually,
barring accidents, arrive in London in four and a half days after
leaving Manchester.” According to the Lord Chancellor of the time such
swift travelling was considered dangerous as well as wonderful--the
condition of the roads might well make it so--and also injurious to
health. “I was gravely advised,” he says, “to stay a day in York on my
journey between Edinburgh and London, as several passengers who had
gone through without stopping had died of apoplexy from the rapidity
of the motion.”
As the coach took a fortnight to pass from the Scotch to the English
capital, at an average pace of between three and four miles an hour,
it is probable that the Chancellor’s advisers would be very seriously
indisposed by the mere sight of a motor-car whirling along in its
attendant cloud of dust, could they be resuscitated for the purpose.
And we, on the other hand, should prefer to get out and walk to
“flying” at the safe speed of their mail coaches.
[Illustration: _By kind permission of The Speedwell Motor Co._
_M. Serpollet on the “Easter Egg,” which at Nice covered a kilometre
in the record time of 29-4/5 secs. (over 75 miles per hour). This car
is run with steam._]
The improvement of highroads, and road-making generally, accelerated
the rate of posting. In the first quarter of the nineteenth century an
average of ten or even twelve miles an hour was maintained on the Bath
Road. But that pace was considered inadequate when the era of the
“iron horse” commenced, and the decay of stage-driving followed hard
upon the growth of railways. What should have been the natural
successor of the stage-coach was driven from the road by ill-advised
legislation, which gave the railroads a monopoly of swift transport,
which has but lately been removed.
The history of the steam-coach, steam-carriage, automobile,
motor-car--to give it its successive names--is in a manner unique,
showing as it does, instead of steady development of a practical means
of locomotion, a sudden and decisive check to an invention worthy of
far better treatment than it received. The compiler of even a short
survey of the automobile’s career is obliged to divide his account
into two main portions, linked together by a few solitary engineering
achievements.
The first period (1800-1836), will, without any desire to arrogate for
England more than her due or to belittle the efforts of any other
nations, be termed the English period, since in it England took the
lead, and produced by far the greatest number of steam-carriages. The
second (1870 to the present day) may, with equal justice, be styled
the Continental period, as witnessing the great developments made in
automobilism by French, German, Belgian, and American engineers:
England, for reasons that will be presently noticed, being until quite
recently too heavily handicapped to take a part in the advance.