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 assumes under different degrees of heat. We see water passing from solid ice to liquid water and gaseous steam, by a mere rise in temperature, and conversely, by abstraction of heat, steam passes 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 pronounced illustration 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 passing 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 illustration, 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 illustration 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 substitutes 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 illustration 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 passing 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 passes off with them in a constant flow, while the vapor of ether is condensed into a liquid again by the cold water, and passing 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 passing 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.

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.

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 passing through the pipes while the other passes through the spaces 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 passing 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 passes 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 quantity 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 balls were coated with sulphuric acid to increase the absorbing surfaces, and which apparatus was effective in freezing considerable quantities 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 CarrÉ’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.

Probably the earliest practical ice machine to be organized on a commercial basis was the ammonia absorption machine of Ferdinand CarrÉ, which was a continuously working machine. It is disclosed in French patents Nos. 81 and 404, of 1860, and No. 75,702, of 1867; United States patent No. 30,201, October 2, 1860. In this case advantage is taken first of the very volatile character of anhydrous ammonia, in the expansion part of the process, and, secondly, of the great affinity which water has for absorbing such gas. Strange as it may appear, the production of ice in the CarrÉ process begins with the application of heat. It must be understood, however, that this forms no part of the refrigerating process proper, but only a means of driving off or distilling the anhydrous ammonia gas (the refrigerant) from its aqueous solution. Ammonia dissolved in water, known as aqua ammonia, is placed in a boiler or still above a furnace. The pure ammonia gas is thus driven off from the water by heat under pressure, similar to that in a steam boiler, and passes direct to a condenser, where, by cold water flowing through pipes, the pure gas is liquefied under pressure. The liquefied gas is then admitted to the evaporating or refrigerating chamber, where it expands to produce the cold, and is afterward re-absorbed by the water from which it was originally driven off in the still, to be used over again. Machines of this type are known as absorption machines, for the reason that the volatile gas is after expansion re-absorbed by the liquid in which it was dissolved, and is continuously driven off therefrom by the heat of a still. Absorption machines were the outgrowth of Faraday’s observations in 1823. A bent glass tube was prepared containing at one end a quantity of chloride of silver, saturated with ammonia and hermetically sealed. When the mixture was heated, the ammonia was driven over to the other end of the tube, immersed in a cold bath, and the ammonia gas became liquefied. It was found by him then that if the end containing the chloride was plunged in a cold bath and the end containing liquid ammonia was immersed in water, the heat of the water made the ammonia rapidly evaporate, the chloride at the other end of the tube absorbed the ammonia vapors, and the water around the end of the tube containing the liquefied ammonia was converted into ice, by the loss of its heat imparted to the ammonia to volatilize it. It only needed the substitution of water for the chloride of silver, as an absorbing agent for the ammonia, and mechanical means for economically working the process in a continuous way to produce the CarrÉ absorption machine. The most common form of ice machine to-day is, however, what is known as the compression or direct system, in which the absorption principle is dispensed with, the ammonia being compressed by powerful steam pumps, then cooled to liquid form by condensers, and then allowed to expand from its own pressure through pipes immersed in brine in a large floor tank, in which cans containing pure water are immersed, and the water frozen. Fig. 296[5] shows the compression pumps, and Fig. 297 the floor tanks, of such a system. Many hundred cans filled with pure water are lowered into the cold brine of the tank, and their upper ends form a complete floor, as seen in Fig. 297. When the water in the cans is frozen, the cans are raised out of the floor by a traveling crane and carried to one of the four doors seen at the far end of the room. The ice in the can is then loosened by warm water, and the block dumped through the door into a chute, whence it passes into the storage room below, seen in Fig. 298. In the can system the water is frozen from all four sides to the center, and imprisons in the center any air bubbles or impurities that may exist in the water. The plate system freezes the water on the exterior walls of hollow plates, which contain within them the freezing medium. In freezing the water externally on these plates all impurities and air bubbles are repelled and excluded, and the ice rendered clear and transparent.

An ice plant, employing what is known as the “can” system and capable of producing 100 tons of ice in twenty-four hours, requires a building about 100 feet wide and 150 feet long, on account of the great floor space needed to accommodate the freezing tank, and the great number of cans which are immersed in the same. A radical departure from this style of plant is presented in the Holden ice machine. This does not require a multitude of cans and a great floor space, but a lot 25 by 50 feet is sufficient, for the ice is turned out in a continuous process like bricks from a brick machine. The machine works on the ammonia absorption principle, but the freezing is done on the outer periphery of a revolving cylinder, from which the film of ice is scraped off automatically and the ice slush carried away by a spiral conveyor to one of two press molds, in which a heavy pressure solidifies the ice into blocks, which are successively shot down from the presses on a chute to the storage room, as seen in Fig. 299.

The foregoing examples of ice machines give no idea of the great activity in this field of refrigeration in the Nineteenth Century. Over 600 United States patents have been granted for ice machines alone, to say nothing of refrigerating buildings, refrigerator cars, domestic refrigerators, and ice cream freezers, etc. Among the earlier workers in ice machines, in addition to those already named, may be mentioned the names of Gorrie, patent No. 8,080, May 6, 1851, followed by Twining, 1853-1862; Mignon and Rouart, in 1865; Lowe, in 1867; Somes, in 1867-1868; Windhausen, in 1870; Rankin, in 1876-1877, and many others.An application of the ice machine which attracted much attention and attained great popularity for a while was that made in the production of artificial skating rinks, in which a floor of ice was frozen by means of a system of submerged pipes, through which the cold liquid from the ice machine was made to circulate. The earliest artificial skating rink is to be found in the British patent to Newton, No. 236, of 1870, but it was Gamgee, in 1875 and 1876, who devised practical means for carrying it out and brought it into public use. His inventions are described in his British patents No. 4,412, of 1875, and No. 4,176, of 1876, and United States patent. No. 196,653, October 30, 1877, and others in 1878.The Windhausen machine was one of the earliest applications for cooling and ventilating ships. This machine operated upon the principle of alternately compressing and expanding air, and is described in United States patents No. 101,198, March 22, 1870 (re-issue No. 4,603, October 17, 1871), and No. 111,292, January 24, 1871. To-day every ocean liner is equipped with its own cold storage and ice-making plant, refrigerator cars transport vast cargoes of meats, fish, etc., across the continent, and bring the ripe fruits of California to the Eastern coast; every market house has its cold storage compartments, and to the brewery the refrigerating plant is one of its fundamental and important requisites.

The great value of refrigerating appliances is to be found in the retardation of chemical decomposition or arrest of decay, and as this has relation chiefly to preserving the food stuffs of the world, its value can be easily understood. This branch of industry has grown up entirely in the Nineteenth Century, and the activity in this field is attested by the 4,000 United States patents in this class.