[Ill.u.s.tration: FIG. 288.--COTTON GIN.]

[Ill.u.s.tration: FIG. 289.--MODERN SPINNING SPINDLE.]

A modern step of importance in spinning was the _ring frame_. Ring spinning was invented by John Thorp, of Rhode Island, who took out two patents for the same November 20, 1828. The leading feature of the ring frame is the subst.i.tution of a light steel hoop or traveler running upon the upper edge of a ring surrounding the spindle in lieu of the flyer formerly employed. The thread pa.s.ses through the hoop as it is wound upon the spindle. In modern times ring spinning has attained considerable proportions, especially in cotton manufactures.

Nearly 3,000 United States patents have been granted in the cla.s.s of spinning, and many valuable improvements in the details of construction in spinning machinery have been made in recent years. The most important, perhaps, are those relating to spindle structure, whereby the speed and efficiency of spinning machines have been greatly increased.

Prior to 1878 the speed of the average spindle was limited to 5,000 revolutions a minute. In 1878 improvements were made which doubled its working speed and permitted as high as 20,000 revolutions a minute. This result was accomplished by making a yielding bolster. The bolster is an upright sleeve bearing, in which the spindle revolves, and against which is sustained the pull of the band that drives the spindle. By making this bolster or sleeve bearing to yield laterally by means of an elastic packing which surrounds it, a much greater freedom and speed of revolution were obtained. The preliminary step in this direction was made by Birkenhead in patent No. 205,718, July 9, 1878. In the same year this idea was perfected by Rabbeth. The bolster was placed loosely in a bolster case of slightly larger diameter than the bolster, and the bottom of the spindle had a free lateral movement as well as the top, as shown in his patent No. 227,129, May 4, 1880. With such perfect freedom of movement, the spindle at high speed could find its own center of revolution, and an indefinitely high speed and quadrupled efficiency were attained. The Draper Spindle is shown in Fig. 289 as one of the most modern and representative of spinning spindles. Considering the great speed of the modern spindle and the fact that a single workman attends a thousand or more of them, the record of progress in this art becomes impressive. In 1805 there were only 4,500 cotton spindles at work in the United States. In 1899 there were 18,100,000.

_Weaving._--A woven fabric consists of threads which run lengthwise, called the "warp," crossed by threads running transversely, called the "woof," "weft," or "filling," which latter are imprisoned or locked in by the warp. In a simple loom the warp threads are divided into two groups, the threads of one group alternating with those of the other, and means are provided for separating these groups to form a wedge-shaped s.p.a.ce between them called a "shed." Through this shed the shuttle which carries the woof or filling thread is sent crosswise the warp threads. Means are provided for changing the inclination and position of the two groups of warp threads in relation to each other, so as to lock in the filling, and put the warp threads in position to receive the next filling thread. For this purpose the warp threads, usually horizontal, are each pa.s.sed through a loop, and every alternate loop is attached to a frame called a "heddle." The intervening loops and threads are attached to another frame or "heddle," and the two heddles by being worked, one up and the other down, separate the warp threads to form the shed. Formerly the shuttle was thrown by hand through the shed.

In 1733 John Kay, of England, took out British patent No. 542, for the flying shuttle and picking stick, by which the shuttle was struck a hammer-like blow and driven like a ball from a bat across the warp, and was struck by a similar stick on the other side, to be returned in the same way. This gave a much more rapid action than could be obtained by hand-throwing, and enabled one weaver to do the work of two or three. In 1760 Robert Kay invented the drop box, by which different shuttles carrying different colors of thread were employed.

The _power loom_, however, marked the first great growth in the art of weaving. The enormously increased quant.i.ty of cotton spun by Arkwright's machinery made a demand for increased facilities for weaving it into cloth. Dr. Cartwright, of England, foresaw and met this demand in his _power loom_, in which all of the intricate operations were performed by power-driven machinery. His invention was not extensively introduced until about the beginning of the Nineteenth Century. One difficulty experienced was that the warp threads, from their fuzzy nature, had to be dressed with size, and this required the loom to be stopped from time to time, and necessitated the services of a man to dress or size the warp threads. This difficulty was overcome, however, by Johnson & Radcliffe, about 1803, by the sizing and dressing of the yarns by pa.s.sing them between rollers and coating them with a thin layer of paste before being put into the loom. Dr. Cartwright was granted British patents No. 1,470, of 1785; No. 1,565, of 1786; No. 1,616, of 1787, and No. 1,676, of 1788, but being unable to maintain any monopoly under his patents he was compensated by Parliament with a grant of 10,000.

[Ill.u.s.tration: FIG. 290.--MODERN JACQUARD LOOM.]

_Jacquard Loom._--This most notable step in the art of weaving was made at the very beginning of the Nineteenth Century. It enabled all kinds of fabrics, from the finest to the coa.r.s.est, to be cheaply woven into patterns having figured or ornamental designs. Jacquard, a native of Lyons, conceived the plan of his great invention in the last decade of the Eighteenth Century, and on December 28, 1801, took out French patent No. 245, on the same. His invention was not, in fact, a new form of loom, but rather an attachment to a loom which was universally applicable to all looms. Before his invention, figured patterns of cloth could only be made by slow and laborious processes. Jacquard's invention consisted in individualizing and differentiating the movement of the warp threads, instead of operating them in constant groups. This individualizing of the movement of the warp threads allowed any warp thread to be held up automatically any length of time, or let down, according as was necessary to form the figure of the pattern. This was accomplished by making a chain of articulated cards, like a slatted belt, and perforating these cards with varying arrangements of holes.

The cards were successively and intermittently fed to a set of needles, which latter, by rising and falling, raise or lower the warp threads attached to the same. By perforating these cards differently, and arranging them so that when one card was brought in front of the needles it would let certain needles through the perforations and hold the others back, it will be seen that each card controlled the action of a different set of needles, and the sequence of the series of cards effected the necessary change in the needles and movement of the warp threads to form the growth of the figure in the fabric.

In Fig. 290 is seen a modern form of Jacquard loom, showing at the far end the chain of perforated cards. Jacquard received a bronze medal at the French Exposition in 1801, was decorated with the Cross of the Legion of Honor, and the grat.i.tude of his countrymen was attested by a pension of 6,000 francs, and a statue erected to his memory at Lyons in 1840.

Subsequent improvements and developments of the Jacquard loom have carried its work to great nicety and refinement of action. In the chain of pattern cards it is said that as many as 25,000 separately punched cards or plates are sometimes used in weaving a single yard of brocade.

The great variety of elaborate designs of delicate tracery in silk, rich patterns in brocades, and gorgeous figures in carpets, attest the value of Jacquard's important step in this art.

Nearly 5,000 United States patents have been granted in the cla.s.s of weaving. In the early part of the century much notable work was done.

Steam was applied to looms by William Horrocks (British patent No.

2,699, 1803). From 1830 to 1842 there were brought out the fancy looms of Crompton, the application of the Jacquard mechanism to the lace frame by Draper, and the carpet looms of Bigelow. In 1853 Bonelli sought to improve on the Jacquard mechanism by employing electro-magnets to effect the selection of the needles, instead of perforated cards (British patent No. 1,892, of 1853).

Among more recent developments is the _Positive Motion_ loom of Lyall, patented December 10, 1872, No. 133,868, re-issue No. 9,049, January 20, 1880. The distinguishing feature of this is that the shuttle is not thrown or impelled as a projectile through the wedge-shaped s.p.a.ce (shed), between the two sets of warp threads, but is positively dragged back and forth through the same by an endless belt attached to the shuttle carriage and running first in one direction and then in the other to drag the shuttle through.

[Ill.u.s.tration: FIG. 291.--CROMPTON FANCY LOOM.]

It is not to be understood that the positive motion loom has superseded the flying shuttle. The latter is still the leading type, of which the Crompton fancy loom, shown in Fig. 291, is a representative ill.u.s.tration.

The tendency in late years in the art of weaving has been toward labor-saving devices, a reduction in the cost to the consumer of all kinds of textile fabrics, and the extension of the loom to the weaving of new kinds of materials. Prominent among these are the inventions in the loom for weaving plain fabrics made between the years 1881 and 1895, shown in patents to Northrop, No. 454,810, June 23, 1891; No. 529,943, November 27, 1894, and Draper, No. 536,948, April 2, 1895. This loom, as usual, employs a single shuttle, but as the weft becomes exhausted another bobbin is automatically supplied to the shuttle without stopping the operation of the machine. During the year 1895 the first loom for weaving an open mesh cane fabric having diagonal strands was invented. Patents to Morris, No. 549,930, and to Crompton, No. 550,068, November 19, 1895, were obtained for this. Prior to this time two distinct machines were necessary to produce this fabric, and the operation was slow and expensive. Between 1893 and 1895 two machines were invented, upon either of which the well-known Turkish carpets can be woven. Patents to Youngjohns, No. 510,755, December 12, 1893, and to Reinhart von Seydlitz, No. 533,330, January 29, 1895, disclose this. The drawing of warp threads into the eyes of the heddles and through the reed of a loom requires great skill, and prior to 1880 was performed by hand at great expense. In 1882, however, a machine for doing this was invented, thereby dispensing with the old hand method and cheapening the operation. Patents to Sherman and Ingersoll, No. 255,038, March 14, 1882, and Ingersoll, No. 461,613, October 20, 1891, were granted for this machine.

To-day the shuttle flies at the rate of 180 to 250 strokes a minute, and yet the complex organization of the machine works with an energy, a uniformity, an accuracy and a continuity that leaves far behind the strength of the arm, the memory of mind, and the accuracy of the human eye, and yet, if the tiny thread breaks, the whole organization instantly stops and patiently waits the remedial care of its watchful master.

_Knitting Machines._--Knitting differs from weaving, braiding, or plaiting in the following respects: In weaving there are longitudinal threads called warp threads, which are crossed on a separate weft or filling thread. In braiding or plaiting all the threads may be considered warp threads, since they are arranged to run longitudinally, and instead of locking around a separate transverse thread at right angles, they extend diagonally and are interwoven with each other. In netting and knitting, however, there is but a single thread, which, in netting, is knotted into itself at definite intervals to leave a mesh of definite size, while in knitting the single thread is merely looped into itself without any definite mesh. Knitted goods have the peculiarity of great elasticity in consequence of this formation of the fabric, and for that reason find a special application in all garments which are required to snugly conform to irregular outlines, such as stockings for the feet, gloves for the hands, and underwear for the body.

Weaving, braiding, and netting are very old arts, but the art of knitting is comparatively modern. It is believed to have originated about the year 1500 in Scotland. In 1589 William Lee, of England, is credited with making the first knitting machine. It is said that the girl with whom he was in love, and to whom he was paying his attention, was so busy with her work of hand knitting that she could not give him the requisite attention, and he invented the knitting machine that they might have more time to devote to their love affairs. Another version is that he married the girl and invented the machine to relieve her weary fingers from the work of the knitting needle, and still another is that the machine was the leading object of his affections, to the neglect of his sweetheart, who "gave him the mitten" before he had knitted one on his machines.

[Ill.u.s.tration: FIG. 292.--BRANSON 15/16 AUTOMATIC KNITTER.]

The earliest circular knitting machine was by Brunel, described in British patent No. 3,993, of 1816. Power was applied to the knitting frame by Bailey in 1831, and the latch needle was patented in the United States by Hibbert, January 9, 1849, No. 6,025. This patent was extended for seven years from January 9, 1863, and covered a very important and universally used feature of the knitting machine. Research has shown, however, that the latch was not broadly new with Hibbert, as it appeared in the French patent to Jeandeau, No. 1,900, of April 25, 1806. Among the earlier knitting machines, the straight reciprocating type was most in evidence, and of which the Lamb machine was a popular form. The increased speed and capacity of the circular machine have, however, caused it to largely supersede the others. In the circular machine a circular series of vertical parallel needles slide in grooves in a cylinder, and are raised and lowered successively by an external rotating cylinder which has on the inner side cams that act upon the needles. The Branson 15/16 Automatic Knitter, shown in Fig. 292, is a good modern ill.u.s.tration. It performs automatically fifteen-sixteenths of the various movements which ordinarily would be performed by hand on a hand machine. Its salient features are covered by patents No. 333,102, December 29, 1885, and No. 519,170, May 1, 1894. About 2,000 United States patents have been granted in the cla.s.s of knitting and netting, and the value of hosiery and knit goods in the United States in 1890 was $67,241,013.

An important branch of the textile art is cloth finishing, whereby the rough surface of the cloth as it comes from the loom is rendered soft and smooth. One method is to raise the nap of the cloth by pulling out the fibre by a mult.i.tude of fine points. Originally this was done by combing it with teasles, a sort of dried burr of vegetable growth, having a mult.i.tude of fine hook-shaped points. Machines with fine metal card teeth are now largely used for this purpose, and of which the planetary napping machine of Ott, patent No. 344,981, July 6, 1886, is an example. Another method of finishing the cloth is to iron or press it. Plate presses were first used in which smooth plates were folded in alternate layers with the cloth and pressure then applied, but in later years continuous rotary presses have been employed, that of Gessner, patent No. 206,718, August 6, 1878, re-issue No. 9,076, 9,077, February 17, 1880, is one of the earliest examples of a continuous rotary press.

The old Gessner presses of Saxony were the pioneers in this field. A modern Gessner cloth press is seen in Fig. 293.

[Ill.u.s.tration: FIG. 293.--MODERN "GESSNER" CLOTH PRESSING MACHINE.]

In the field of textiles there are many related arts and machines. There are hat felting and finishing machines, darning machines, quilting machines, embroidering machines, processes and apparatus for dyeing and sizing, machines for printing fabrics, machines for making rope and cord, machines for winding and working silk, and in treating the raw material there are cotton-pickers, cotton baling presses, cotton openers and cleaners, flax brakes and hackling machines, feeding devices, wool carding and cleaning apparatus, all in variety and numbers that defy both comment and count.

In fabrics every cla.s.s of fibre has been called into requisition. Flax, wool, silk, and cotton have been supplemented with the fibres of metal, of gla.s.s, of cocoanut, pine needles, ramie, wood-pulp, and of many other plants, leaves and gra.s.ses.

_Artificial silk_ is made out of a chemically prepared composition, and the fibres are spun by processes simulating not only the act of the silkworm, but its product in quality. Vandura silk was spun from an aqueous solution of gelatine by forcing it through a fine capillary tube, but it attained little or no practical value. A far more important artificial silk is covered by the patents to De Chardonnet, No.

394,559, December 18, 1888; No. 460,629, October 6, 1891, and No.

531,158, December 18, 1894, and also in subsequent patents to Lehner and to Turk. These all relate to the manufacture of artificial silk by spinning threads or filaments from pyroxiline (solution of gun cotton), collodion, or some such glutinous solution which evaporates rapidly, leaving a tiny thread, having most of the characteristics of silk and produced by the same method employed by the silk worm when it expresses and draws out its viscid liquid. The De Chardonnet artificial silk took a "Grand Prix" at the Paris Exposition in 1889, and the industry is growing to considerable proportions. Large works are in operation at Besancon, in France, producing 7,000 pounds per week, and it is said that the plant is to be increased to a capacity of 2,000 pounds a day.

Similar works at Avon, near Coventry, England, have an equal capacity, and other factories are about to be established in Belgium and Germany.

_Polished_ or _diamond cotton_ is a l.u.s.trous looking article of a soft silky nature, formed by plating the threads with a liquid emulsion of a waxy and starchy substance, and polishing the threads with rapidly revolving brushes.

_Mercerized Cloth._--In late years a distinct novelty has appeared on the shelves of the dry goods stores. Beautiful, filmy fabrics, and l.u.s.trous embroidery thread, not of silk, but so close to it in appearance as to be scarcely distinguishable, have gained much popularity and attained a large sale. They are known as _mercerized_ goods. About the middle of the century John Mercer, of England, found that when cotton goods were treated with chemicals (either alkalies or acids), a change was produced in the fibre which caused it to shrink and become thicker, and which imparted also an increased affinity for dyes.

He took out British patent No. 13,296, of 1850, for his invention, but practically nothing further was done with the process. Recently the important step of Thomas and Prevost of mercerizing under tension gave some new and wonderful results. United States patents No. 600,826 and No. 600,827, of May 15, 1898, disclose this process. The cloth or thread, while being treated chemically, is at the same time subjected to a powerful tension that causes the fibres (softened and rendered glutinous by the chemicals) to be elongated or pulled out like fibres of molten gla.s.s, giving it the same striated texture and fine l.u.s.ter that silk has, and by substantially the same mechanical agency, for it is the elongation of the plastic glutinous thread from the silk worm that gives the thread its silky l.u.s.ter, by a process which has a familiar ill.u.s.tration in the molecular adjustment that imparts l.u.s.ter to spun gla.s.s or drawn taffy.

Standing in the light of the Twentieth Century, and looking back through past ages, we find the art of spinning and weaving in an ever present and unbroken thread of evidence all along the path of history--through wars and famine, floods and conflagrations; through the progress and decay of nations, through all phases of change, and the vicissitudes of centuries, it has never been relegated to the domain of the lost arts, but has remained a persisting invention. It has been a paramount necessity to the human race, indissolubly locked up with its continuity and welfare, and will ever continue to supply its work in maintaining the greater fabric of human existence.

CHAPTER x.x.xII.

ICE MACHINES.

GENERAL PRINCIPLES--FREEZING MIXTURES--PERKINS' ICE MACHINE, 1834-- PICTET'S APPARATUS--CARRe'S AMMONIA ABSORPTION PROCESS--DIRECT COMPRESSION AND CAN SYSTEM--THE HOLDEN ICE MACHINE--SKATING RINKS-- WINDHAUSEN'S APPARATUS FOR COOLING AND VENTILATING SHIPS.

Very few people have any correct conception of the principles of ice-making. Most persons have heard in a vague sort of way that chemicals are employed in its manufacture, and many a fastidious individual has been known to object to artificial ice on the ground that he could taste the chemicals, and that it could not therefore be wholesome. Such is the power of imagination, and such the misconception in the public mind. Nothing could be more erroneous, nor more amusing to the physicist, since no chemicals ever come in contact with either the water or the ice. An intelligent understanding of the operations of an ice machine involves only a correct appreciation of one of the physical laws governing the relation of heat to matter, and the forms which matter a.s.sumes under different degrees of heat. We see water pa.s.sing from solid ice to liquid water and gaseous steam, by a mere rise in temperature, and conversely, by abstraction of heat, steam pa.s.ses back to water, and then to ice.

When one's hands get wet they get cold. A commonplace, but convenient proof of this is to wet the finger in the mouth and hold it in the air.

A sensible reduction of temperature is instantly noticeable. A more p.r.o.nounced ill.u.s.tration is to wet the hands in a basin of water, and then plunge them in the blast of hot, dry air coming from a furnace register. Instead of warming the hands, as many would suppose, this will, as long as the hands are wet, produce a distinct sensation of increased cold. It is due to rapid evaporation, which in changing the water from a liquid to a gaseous form, abstracts heat from the hands.

Evaporation may be effected in two ways. The common one is by applying extraneous heat, as under a tea kettle, in which case the evaporated vapor is hot by virtue of the heat absorbed from the fire. The other way is to reduce pressure or produce a partial vacuum over the liquid without any application of heat, in which case the vapor is made cold.

As early as 1755 Dr. Cullen observed this, and discovered that the cold thus produced was sufficient to make ice. An incident of evaporation is the pa.s.sing from the limited volume of a liquid to the greatly increased volume of a gas. Water, for instance, when it changes to a vapor, increases in volume about 1,700 times; that is, a cubic inch of water makes about a cubic foot of steam, and when evaporation takes place from a reduction of pressure, this involves a dissipation of heat throughout the increased volume, and the corresponding production of cold. When, however, matter changes from a liquid to a gas, or from a solid to a liquid, a peculiar phenomenon manifests itself, in that a great amount of heat is absorbed and, so far as the evidence of the senses goes, disappears in the mere change of state. It is called _latent heat_. In such case the heat becomes hidden from the senses by being converted into some other form of intermolecular force not appreciable as sensible heat, and producing no elevation of temperature. In ill.u.s.tration, if a pound of water at 212 F. be mixed with a pound of water at 34 (both being matter in the same state), there results two pounds of water at the mean temperature of 123. If, however, a pound of water at 212 be mixed with a pound of _ice_ at 32 (matter in another state), there will not be two pounds of water at the mean temperature of 122, as might be expected, but two pounds at 51 only, an amount of heat sufficient to raise two pounds of water 71 being absorbed in the mere change of ice to water without any sensible raise in temperature. This absorbed heat is called latent heat, and it plays an important part in artificial freezing. A familiar ill.u.s.tration of the absorption of heat in changing from a solid to a liquid is found in the admixture of salt and ice around an ice-cream freezer. These two solids, when brought together, liquefy rapidly with an absorption of heat that produces in a limited time a far greater degree of cold than that which could be obtained from the ice by mere conduction, since the reduction of temperature proceeds faster by liquefaction than can be compensated for by the absorption of heat from the air. Were this not true, ice cream could not be frozen by a mixture of salt and ice. Many such freezing mixtures are known, and a few have been made commercially available, but they cannot be economically employed in ice-making, and it is therefore only necessary to consider the development of the more common principle of evaporation and expansion, in which the change from a liquid to a gas occurs. The volatile liquid which was first employed was water, but as it did not vaporize as readily as some other liquids, more volatile subst.i.tutes were soon found, among which may be named ether, ammonia, liquid carbonic acid, liquid sulphurous acid, bisulphide of carbon and chymogene, which latter is a petroleum product lighter and more volatile than benzine or gasoline. As these liquids were expensive, it is obvious that their vaporization could not be allowed to take place in the open air, since the reagent would thus be quickly dissipated and lost, and hence means were devised to condense and save this valuable volatile liquid to be used over again. The vaporization of the volatile liquid to produce cold, and its re-condensation to liquid form to be used over again in an endless cycle of circulation, seems to have been first effected by Mr. Perkins, of England, whose British patent No. 6,662, of 1834, affords a simple and clear ill.u.s.tration of the fundamental principles of most modern ice machines. His apparatus is shown in Fig.

294. A tank _a_ is filled with water to be frozen or cooled. A refrigerating chamber _b_, submerged in the water, is charged internally with some volatile liquid, such as ether. When the piston of suction pump _c_ rises a partial vacuum is formed beneath it, and the volatile liquid in _b_ being relieved of pressure, evaporates and expands into greater volume, the vapor pa.s.sing out through pipe _f_ and upwardly opening valve _e_. This vapor is rendered intensely cold by expansion, and this cold is imparted to the water in tank _a_ to freeze it. A more scientific statement, however, is that the cold vapor absorbs the heat units of the water, and taking them away with it, lowers the temperature of the water to the freezing point. When the piston of pump _c_ descends, valve _e_ closes, and the vapor, laden with the heat units absorbed from the water, is forced through the downwardly opening valve _e'_, and through pipe _g_ to a cooling coil _d_, around which a body of cold water is continually flowed. This water, in turn, takes the heat units from the vapor, and pa.s.ses off with them in a constant flow, while the vapor of ether is condensed into a liquid again by the cold water, and pa.s.sing through a weighted valve _h_, goes into the evaporating or refrigerating chamber to be again vaporized in an endless circuit of flow. It will be seen that the heat units from the water in tank _a_ are first handed over to the cold ether vapors pa.s.sing out from chamber _b_, and by this vapor are then transferred to the flowing body of water surrounding the coil _d_. The result is that the heat units carried off by the water flowing around coil _d_ are the same heat units abstracted from the water in tank _a_, which water is thus reduced to congealation.

[Ill.u.s.tration: FIG. 294.--PERKINS' ICE MACHINE, 1834.]

Among later ice machines of this type the Pictet machine was a conspicuous example. This employed anhydrous sulphurous acid as the volatile agent, and is described in United States patent No. 187,413, February 13, 1877; French patent No. 109,003, of 1875.

[Ill.u.s.tration: FIG. 295.--THE PICTET ICE MACHINE.]

In Fig. 295 is represented a vertical longitudinal and also a vertical transverse section of a Pictet ice machine. A is a double acting suction and compression pump, D and E are two cylinders which are similarly constructed in the respect that they are both provided with flue pipes and heads for a double circulation of fluids, one fluid pa.s.sing through the pipes while the other pa.s.ses through the s.p.a.ces between the pipes, much like the condenser of a steam engine. The cylinder D is the refrigerator where the volatile liquid is evaporated to produce cold, and the cylinder E is the condenser where the gasified vapor is cooled and condensed again to liquid form to be returned to the refrigerator.

The action is as follows: The pump A by pipe B draws from the chamber in the refrigerator D containing the volatile liquid, causing it to evaporate and produce an intense degree of cold which is imparted to the liquid surrounding it and filling the tank. This liquid is either brine, or a mixture of glycerine and water, or a solution of chloride of magnesium, or other liquid which does not freeze at a temperature considerably below the freezing point of water. Now, this non-congealable liquid being below the freezing point, it will be seen that if cans H be filled with pure water, and are immersed in this intensely cold non-congealable liquid, the water in the cans will freeze. This is exactly what takes place, and this is how the ice is formed. As the volatile liquid is drawn out of the refrigerator D through pipe B by the pump A it is forced by the pump through pipe C and into the chamber of the condenser E. A current of cold water is kept flowing around the pipes in E, coming in through a pipe at one end and pa.s.sing out through a pipe at the other end. The compressed and relatively hot gases are by the contact of this cold water along the sides of the pipes cooled and condensed into a liquid again, which pa.s.ses up the small curved pipe F and is returned to the refrigerator D, to be again evaporated by the suction of the pump to continue the production of cold. In large plants the non-congealable liquid and cans of water to be frozen are (in order to get larger capacity) carried to a large floor tank in a removed situation.

One of the earliest methods of producing ice in a limited quant.i.ty was by evaporating water by a reduction of pressure and causing the vapor to be absorbed by sulphuric acid, which has a great affinity for the water vapor. Mr. Nairne, in 1777, was the first to discover the affinity that sulphuric acid had for water vapor, and in 1810 Leslie froze water by this means. In 1824 Vallance obtained British patents No. 4,884 and 5,001, operating on this principle, in which leaden b.a.l.l.s were coated with sulphuric acid to increase the absorbing surfaces, and which apparatus was effective in freezing considerable quant.i.ties of ice.

The _carafes frappees_ of the Parisian restaurant were decanters in which water was frozen by being immersed in tanks of sea water whose temperature was reduced below freezing by the vaporization of ether in a reservoir immersed in the sea water. Edmond Carre's method of preparing _carafes frappees_ involved the use of the sulphuric acid principle of absorption, and to that end the aqueous vapor was directly exhausted from the decanter by a pump, and the said vapor was absorbed by a large volume of sulphuric acid so rapidly as to freeze the water remaining in the decanter.

[Ill.u.s.tration: FIG. 296.--COMPRESSION PUMPS OF ICE PLANT.]