ICE (Fn., Clare ; GER., Eis).
Ice is too familiar an object to require definition. This article will be divided into two sections, treating (1) of the trade in natural ice, and (2) of the artificial production of ice, and refrigeration generally.
Natural Ice.—Some of the colder countries, as N. America and Scandinavia, have what is called an " ice-harvest " every year. When the ice en the lakes and fjords is about 1 ft. thick, tho snow and rough aurfaee-ice are carefully planed off by an ice-plane, drawn by horses. This done, a straight groove is cut along one side of the clean ice-sheet, by means of the hand-plough. Then, by means of the awing guide-marker, a continuous series of similar grooves are marked parallel to the first and equidistant from each other. The large ice-plough is next drawn over these grooves, deepening the cut to 12-14 in. The same operation is repeated at right angles to the first grooves, and the blocks are ready for separation. To prevent the water meantime from entering the grooves, and freezing them up, they are firmly caulked with snow, driven down by the caulking-bar. When the two outside rows have been sawed out, the blocks .are lifted upon the adjacent ice, and the remaining rows are separated by breaking-bars. The blocks are then floated to the ice-house, and stored in tiers, carefully covered with pine-shavings.
Fig. 830 shows the principal tools used in the harvesting of natural ice : A, marker, with swing guide ; B, plough, with stationary guide ; C, band-plough ; D, snow-plane ; E, grooving-bar ; F G, strikiug-under bars ; H I J K L, fork splitting-bars ; M, channel hook-bar ; N, ice-saw ; 0 P Q, ice-hooks ; R S T, grapples.
In America, the consumption of ice is truly enormous, being estimated, in the Middle States, at 1600 lb. a year for each individual. The supply is obtained from the rivers and lakes in the interior, the four chief sources being Boston and neighbourhood, the Kennebec region (Maine), Hudson River (New York), and the Upper Schuylkill and Lehigh region (Pennsylvania). The quantity of ice cut on the Hudson River is about 1+ million tons annually, and on the Kennebec and Penobscot and their tributaries, about 1 million tons. For a short time, we too were dependent upon the American continent for our supplies of natural ice ; but the loss and cost in transport rendered the price so high as to be unable to compete with Scandinavian ice, when the latter came into the market, and our imports of ice in 1879 were 166,452 tons, value 139,7141., from Norway, and only 5 tons from all other countries.
Artificial Ice.—Refrigeration, or the artificial production of ice, consists simply in transfer ring the heat of the water (or other body to be frozen) to some other body. Water at 15i° (60° F.) contains an excess of heat beyond that of an equal weight of ice at 0° (32° F.) amounting to 170.65 heat units for each lb., therefore, to reduce the water from the first temperature to the second will necessitate the abstraction of that amount of heat from it ; to reduce 1 ton of water will require the removal of 62,720 heat units, or 2240 lb. x 28 (the difference between 32° and 60° F.). It would still be water. To convert it into ice, it is further necessary to abstract the latent heat, which determines the liquid state of water, amounting to 142.65 beat units for each lb. of water ;
or, for 1 ton, 2240 lb. x 142.65 = 319,536 heat units, bringing the total to 382,256 heat units. It is thus evident that about five times greater expenditure of power is necessary to transform water at the freezing-point into a solid condition (ice), than is necessary to reduce its temperature from the ordinary point to the freezing-point ; and this fact must be borne in mind in the practical applica tion of refrigeration to commercial purposes, where a low temperature will often be as effective as the actual production of ice.
In th'e use of so-called "freezing-mixtures," the reduction of temperature in the body is due to the absorption of its heat by the process of solution suffered by the salts employed. They are principally as follows :— These freezing-mixtures are very useful for application on a email scale, but are not adapted for commercial operations. In selecting bodies for abstracting and absorbing hest with the object of producing refrigeration on an extensive scale, several points require to be taken into consideration. (1) The first is the amount of latent heat absorbed by 1 lb. of the body in changing its state, being 966.1 heat units for watery vapours, 900 for gaseous ammonia, 364.3 for alcohol vapour, 162.8 for ether vapour. The amount of artificial cold produced will be in inverse ratio: thus the formation of 1 ton of ice will necessitate the vaporization of about 395; lb. of water, 4241 lb. of liquid ammonia, 1049f lb. of alcohol, or 2348 lb. of ether. (2) The next important consideration is the degree of facility with which the bodies are vaporized, and the range of temperature within which the vaporization can be readily accomplished, or, in other words, the boiling-point of the body and the tension of its vapour. It is sought to obtain a body having the former as low as is convenient, combined with the latter also moderately low. Many practical difficulties have been encountered through selecting bodies possessing the former quality, without much regard to the latter. Thus, at a temperature of 24° (75° F.), which is often exceeded in town waters in warm countries, the tension of liquid ammonia will be 150-160 lb. a sq. in. ; chloride of methyl, about 80 lb.; methylie ether, 78 lb. ; sulphur dioxide (sulphurous anhydride or oxide), CO lb. These immense pressures necessitate•extreme care in the construction of the apparatus, thereby enhancing the cost ; and the difficulty of keeping the joints tight often occasions loss of material and reduced production. (3) Equally tiecesi.ary to be taken into consideration, is tho condensation of the vaporized body, in order that it may be used over again. This condensation is effected by means of a supply of cold water. In some industries, and in certain localities, the scale of consumption of water for this purpose is such as to altogether preclude the use of certain machines. (4) The chemical properties of the substances employed must be studied in relation to their action upon the metal or other material with which they will come into contact. Having said eo much concerning the general principles and conditions involved in the artificial production of a low temperature, or ice itself, some space may now be devoted to a description of the principal machines devised with this object.