This transformation ill.u.s.trates 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 s.p.a.ce.

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-a.s.sertiveness as to collapse into a liquid ma.s.s, 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.

[Ill.u.s.tration: _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 s.p.a.ce. 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 quant.i.ties 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 pa.s.s 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 pa.s.sed 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 pa.s.s 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 pa.s.ses through a s.p.a.ce 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 quant.i.ty 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--pa.s.ses 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 bra.s.s. Meat, eggs, fruit, and all bodies containing water become hard as steel and as breakable as gla.s.s. Mercury is by it congealed to the consistency of iron; even alcohol, that can brave the utmost Arctic cold, succ.u.mbs 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 gla.s.s 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 s.p.a.ce is less than an inch. This fact is hard to square with the a.s.sertion of scientific men that our atmosphere extends but a hundred or two miles from the earth's surface, and that the recesses of s.p.a.ce 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 depots 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 subst.i.tuted for anaesthetics, 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 a.s.sured 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 acc.u.mulators. The Liquid Air Company have at their Gillingham Street depot 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 pa.s.ses 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 quant.i.ties 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 advertis.e.m.e.nt, 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 pa.s.sengers who had gone through without stopping had died of apoplexy from the rapidity of the motion."

As the coach took a fortnight to pa.s.s 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.

[Ill.u.s.tration: _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.

_Historical._--It is impossible to discover who made the first self-moving carriage. In the sixteenth century one Johann Haustach, a Nuremberg watchmaker, produced a vehicle that derived its motive power from coiled springs, and was in fact a large edition of our modern clockwork toys. About the same time the Dutch, and among them especially one Simon Stevin, fitted carriages with sails, and there are records of a steam-carriage as early as the same century.

But the first practical, and at least semi-successful, automobile driven by internal force was undoubtedly that of a Frenchman, Nicholas Joseph Cugnot, who justly merits the t.i.tle of father of automobilism.

His machine, which is to-day one of the most treasured exhibits in the Paris Museum of Arts and Crafts, consisted of a large carriage, having in front a pivoted platform bearing the machinery, and resting on a solid wheel, which propelled as well as steered the vehicle. The boiler, of stout riveted copper plates, had below it an enclosed furnace, from which the flames pa.s.sed upwards through the water through a funnel. A couple of cylinders, provided with a simple reversing gear, worked a ratchet that communicated motion to the driving-wheel. This carriage did not travel beyond a very slow walking pace, and Cugnot therefore added certain improvements, after which (1770) it reached the still very moderate speed of four miles an hour, and distinguished itself by charging and knocking down a wall, a feat that is said to have for a time deterred engineers from developing a seemingly dangerous mode of progression.

Ten years later Dallery built a steam car, and ran it in the streets of Amiens--we are not told with what success; and before any further advance had been made with the automobile the French Revolution put a stop to all inventions of a peaceful character among our neighbours.

In England, however, steam had already been recognised as the coming power. Richard Trevethick, afterwards to become famous as a railroad engineer, built a steam motor in 1802, and actually drove it from Cambourne to Plymouth, a distance of ninety miles. But instead of following up this success, he forsook steam-carriages for the construction of locomotives, leaving his idea to be expanded by other men, who were convinced that a vehicle which could be driven over existing roads was preferable to one that was helpless when separated from smooth metal rails. Between the years 1800 and 1836 many steam vehicles for road traffic appeared from time to time, some, such as David Gordon's (propelled by metal legs pressing upon the ground), strangely unpractical, but the majority showing a steady improvement in mechanical design.

As it will be impossible, without writing a small book, to name all the English constructors of this period, we must rest content with the mention of the leading pioneers of the new locomotion.

Sir Goldsworthy Gurney, an eminent chemist, did for mechanical road propulsion what George Stephenson was doing for railway development.

He boldly spent large sums on experimental vehicles, which took the form of six-wheeled coaches. The earliest of these were fitted with legs as well as driving-wheels, since he thought that in difficult country wheels alone would not have sufficient grip. (A similar fallacy was responsible for the cogged wheels on the first railways.) But in the later types legs were abandoned as unnecessary. His coaches easily climbed the steepest hills round London, including Highgate Hill, though a thoughtful mathematician had proved by calculations that a steam-carriage, so far from mounting a gradient, could not, without violating all natural laws, so much as move itself on the level!

Having satisfied himself of their power, Gurney took his coaches further afield. In 1829 was published the first account of a motor trip made by him and three companions through Reading, Devizes, and Melksham. The pace was, we read, at first only about six miles an hour, including stoppages. They drove very carefully to avoid injury to the persons or feelings of the country folk; but at Melksham, where a fair was in progress, they had to face a shower of stones, hurled by a crowd of roughs at the instigation of some coaching postilions, who feared losing their livelihood if the new method of locomotion became general. Two of the tourists were severely hurt, and Gurney was obliged to take shelter in a brewery, where constables guarded his coach. On the return journey the party timed their movements so as to pa.s.s through Melksham while the inhabitants were all safely in bed.

The coach ran most satisfactorily, improving every mile. "Our pace was so rapid," wrote one of the company, "that the horses of the mail-cart which accompanied us were hard put to it to keep up with us. At the foot of Devizes Hill we met a coach and another vehicle, which stopped to see us mount this hill, an extremely steep one. We ascended it at a rapid rate. The coach and pa.s.sengers, delighted at this unexpected sight, honoured us with shouts of applause."