in physiology, a solid, transparent, and brittle body, formed of some fluid, particularly water, by means of cold. See Frost.

The younger Lemery observes, that ice is only a re-establishment of the parts of water in their natural state; that the mere absence of fire is sufficient to account for this re-establishment; and that the fluidity of water is a real fusion, like that of metals exposed to the fire; differing only in this, that a greater quantity of fire is necessary to the one than the other. Galileo was the first that observed ice to be lighter than the water which composed it: and hence it happens, that ice floats upon water, its specific gravity being to that of water as eight to nine. This rarefaction of ice seems to be owing to the air-bubbles produced in water by freezing; and which, being considerably large in proportion to the water frozen, render the body so much specifically lighter: these air-bubbles, during their reduction, acquire a great expansive power, so as to burst the containing vessels, though ever so strong. See Congelation, Cold.

M. Mairan, in a dissertation on ice, attributes the increase of its bulk chiefly to a different arrangement of the parts of the water from which it is formed; the icy skin on the water being composed of filaments which, according to him, are found to be constantly and regularly joined at an angle of 60°; and which, by this angular disposition, occupy a greater volume than if they were parallel. He found the augmentation of the volume of water by freezing, in different trials, a 14th, an 18th, a 16th, and when the water was previously purged of air, only a 22d part: that ice, even after its formation, continues to expand by cold; for, after water had been frozen to some thickness, the fluid part being let out by a hole in the bottom of the vessel, a continuance of the cold made the ice convex; and a piece of ice, which was at first only a 14th part specifically lighter than water, on being exposed some days to the frost, became a 12th part lighter. To this cause he attributes the bursting of ice on ponds.

Wax, resins, and animal-fats, made fluid by fire, instead of expanding like watery liquors, shrink in their return to solidity: for solid pieces of the same bodies sink to the bottom of the respective fluids; a proof that these bodies are more dense in their solid than in their fluid state. The oils which congeal by cold, as oil-olive, and the essential oil of aniseeds, appear also to shrink in their congelation. Hence, the different dispositions of different kinds of trees to be burst by, or to resist, strong frosts, are by some attributed to the juices with which the tree abounds; being in the one case watery, and in the other resinous or oily.

Though it has been generally supposed that the natural crystals of ice are stars of six rays, forming angles of 60° with each other, yet this crystallization of water, as it may properly be called, seems to be as much affected by circumstances as that of salts. Hence we find a considerable difference in the accounts of those who have undertaken to describe these crystals. M. Mairan informs us, that they are stars with six radii; and his opinion is confirmed by observing the figure of frost on glass. M. Rome de L'Isle determines the form of the solid crystal to be an equilateral octaedron. M. Haffenratz found it to be a prismatic hexaedron; but M. d'Antic found a method of reconciling these seemingly opposite opinions. In a violent hail-storm, where the hailstones were very large, he found they had sharp wedge-like angles of more than half an inch; and in these he supposed it impossible to see two pyramidal tetraedra joined laterally, and not to conclude that each grain was composed of octaedrons converging to a centre. Some had a cavity in the middle; and he saw the opposite extremities of two opposite pyramids, which constitute the octaedron; he likewise saw the octaedron entire united in the middle; all of them were therefore similar to the crystals formed upon a thread immersed in a saline solution. On these principles M. Antic constructed an artificial octaedron resembling one of the largest hailstones; and found that the angle at the summit of the pyramid was 45°, but that of the junction of the two pyramids 145°. It is not, however, easy to procure regular crystals in hailstones where the operation is conducted with such rapidity: in snow and hoar-frost, where the crystallization goes on more slowly, our author is of opinion that he sees the rudiments of octaedra.

Ice, as is explained under the article Frost, forms generally on the surface of water: but this too, like the crystallization, may be varied by an alteration in the circumstances. In Germany, particularly the northern parts of that country, it has been observed that there are three kinds of ice. 1. That which forms on the surface. 2. Another kind formed in the middle of the water, resembling nuclei or small hail. 3. The ground-ice which is produced at the bottom, especially where there is any fibrous substance to which it may adhere. This is full of cells like a wasp's nest, but less regular; and performs many strange effects in bringing up very heavy bodies from the bottom, by means of its inferiority in specific gravity to the water in which it is formed. The ice which forms in the middle of the water rises to the top, and there unites into large masses; but the formation both of this and the ground-ice takes place only in violent and sudden colds, where the water is shallow, and the surface disturbed in such a manner that the congelation cannot take place. The ground-ice is very destructive to dykes and other aquatic works. In the more temperate European climates these kinds of ice are not met with.

In many countries the warmth of the climate renders ice not only a desirable, but even a necessary article; so that it becomes an object of some consequence to fall upon a ready and cheap method of procuring it. Though the cheapest method hitherto discovered seems to be that related under the article Cold, by means of sal ammoniac or Glauber's salt, yet it may not be amiss to take notice of some attempts made by Mr Cavallo to discover a method of producing a sufficient degree of cold for this purpose by the evaporation of volatile liquors. He found, however, in the course of these experiments, that ether was in- comparably superior to any other fluid in the degree of cold it produced. The price of the liquor naturally induced him to fall upon a method of using it with as little waste as possible. The thermometer he made use of had the ball quite detached from the ivory piece on which the scale was engraved. The various fluids was then thrown upon the ball through the capillary aperture of a small glass vessel shaped like a funnel; and care was taken to throw them upon it so slowly, that a drop might now and then fall from the under part, excepting when those fluids were used, which evaporate very slowly; in which case it was sufficient barely to keep the ball moist, without any drop falling from it. During the experiment the thermometer was kept very gently turning round its axis, that the fluid made use of might fall upon every part of its ball. He found this method preferable to that of dipping the ball of the thermometer into the fluid and taking it out again immediately, or even of anointing it constantly with a feather. The evaporation, and consequently the cold, produced by it, may be increased by blowing on the thermometer with a pair of bellows; though this was not used in the experiments now to be related, on account of the difficulty of its being performed by one person, and likewise because it occasions much uncertainty in the results.

The room in which the experiments were made was heated to 64° of Fahrenheit; and with water it was reduced to 56°, viz. 8° below that of the room or of the water employed. The effect took place in about two minutes; but though the operation was continued for a longer time, it did not sink lower. With spirit of wine it sunk to 48°. The cold was greater with highly rectified spirit than with the weaker sort; but the difference is less than would be expected by one who had never seen the experiment made. The pure spirit produces its effect much more quickly. On using various other fluids which were either compound of water and spirituous liquors or pure essences, he found that the cold produced by their evaporation was generally some intermediate degree between that produced by water and the spirit of wine. Oil of turpentine sunk the mercury three degrees; but olive oil and others, which evaporate very slowly, or not at all, did not sensibly affect the thermometer.

To observe how much the evaporation of spirit of wine, and consequently the cold produced by it, would be increased by electricity, he put the tube containing it into an inflating handle, and connected it with the conductor of an electrical machine, which was kept in action during the time of making the experiment; by which means one degree of cold seemed to be gained, as the mercury now sunk to 47° instead of 48°, at which it had stood formerly. On trying the three mineral acids, he found that they heated the thermometer instead of cooling it; which effect he attributes to the heat they themselves acquired by uniting with the moisture of the atmosphere. The vitriolic acid, which was very strong and transparent, raised the mercury to 12°, the smoking nitrous acid to 72°, and the marine to 60°.

The apparatus for using the least possible quantity of ether for freezing water consists in a glass tube (fig. 1.), terminating in a capillary aperture, which is to be fixed upon the bottle containing the ether. Round the lower part of the neck at A some thread is wound, in order to let it fit the neck of the bottle. When the experiment is to be made, the stopper of the bottle containing the ether is to be removed, and the tube just mentioned put in its room. The thread round the tube ought also to be previously moistened with water or spittle before it is put into the neck of the bottle, in order the more effectually to prevent the escape of the ether betwixt the neck of the vial and tube. Holding then the bottle by its bottom FG (fig. 2), and keeping it inclined as in the figure, the small stream of ether issuing out of the aperture D of the tube DE, is directed upon the ball of the thermometer, or upon a tube containing water or other liquor that is required to be congealed. As ether is very volatile, and has the remarkable property of increasing the bulk of air, there is no aperture requisite to allow the air to enter the bottle while the liquid flows out. The heat of the hand is more than sufficient to force out the ether in a continued stream at the aperture D.

In this manner, throwing the stream of ether upon the ball of a thermometer in such a quantity that a drop might now and then, every ten seconds for instance, fall from the bulb of the thermometer, Mr Cavallo brought the mercury down to 3°, or 29° below the freezing point, when the atmosphere was somewhat hotter than temperate. When the ether is very good, i.e. capable of dissolving elastic gum, and has a small bulb, not above 20 drops of it are required to produce this effect, and about two minutes of time; but the common sort must be used in greater quantity, and for a longer time; though at last the thermometer is brought down by this very nearly as low as by the best sort.

To freeze water by the evaporation of ether, Mr Cavallo takes a thin glass tube about four inches long, and one-fifth of an inch diameter, hermetically sealed at one end, with a little water in it, so as to take up about half an inch of the cavity, as is shown at CB in fig. 3. Into this tube a slender wire H is also introduced, the lower extremity of which is twisted into a spiral, and serves to draw up the bit of ice when formed. He then holds the glass tube by its upper part A with the fingers of the left hand, and keeps it continually and gently turning round its axis, first one way and then the other; whilst with the right hand he holds the phial containing the ether in such a manner as to direct the stream on the outside of the tube, and a little above the surface of the water contained in it. The capillary aperture D should be kept almost in contact with the surface of the tube containing the water; and by continuing the operation for two or three minutes, the water will be frozen as it were in an instant; and the opacity will ascend to C in less than half a second of time, which makes a beautiful appearance. This congelation, however, is only superficial; and in order to congeal the whole quantity of water, the operation must be continued a minute or two longer; after which the wire H will be found kept very tight by the ice. The hand must then be applied to the outside of the tube, in order to soften the surface of the ice; which would otherwise adhere very firmly to the glass; but when this is done, the wire H easily brings it out.

Sometimes our author was accustomed to put into the tube a small thermometer instead of the wire H; and thus he had an opportunity of observing a very curious phenomenon unnoticed by others, viz., that in the winter time water requires a smaller degree of cold to congeal it than in the summer. In the winter, for instance, the water in the tube AB will freeze when the thermometer stands about 30°; but in the summer, or even when the thermometer stands at 60°, the quicksilver must be brought down to 15°, or even more degrees below the freezing point before any congelation can take place. In the summer time therefore a greater quantity of ether, and more time, will be required to congeal any given quantity of water than in winter. When the temperature of the atmosphere has been about 40°, our author has been able to congeal a quantity of water with an equal quantity of good ether; but in summer two or three times the quantity are required to perform the effect. "There seems (says he) to be something in the air, which, besides heat, interferes with the freezing of water, and perhaps of all fluids; though I cannot say from my own experience whether the above mentioned difference between the freezing in winter and summer takes place with other fluids, as milk, oils, wines," &c.

The proportion of ether requisite to congeal water seems to vary with the quantity of the latter; that is, a large quantity of water seems to require a proportionally less quantity of ether to freeze it than a smaller one. "In the beginning of the spring (says Mr Cavallo), I froze a quarter of an ounce of water with about half an ounce of ether; the apparatus being larger, though similar to that described above. Now as the price of ether, sufficiently good for the purpose, is generally about 18d. or 2s. per ounce, it is plain, that with an expense under two shillings, a quarter of an ounce of ice, or ice-cream, may be made, in every climate, and at any time, which may afford great satisfaction to those persons, who, living in those places where no natural ice is to be had, never saw or tasted any such delicious refreshment. When a small piece of ice, for instance, of about ten grains weight, is required, the necessary apparatus is very small, and the expense not worth mentioning. I have a small box four inches and a half long, two inches broad, and one and a half deep, containing all the apparatus necessary for this purpose; viz., a bottle capable of containing about one ounce of ether; two pointed tubes, in case one should break; a tube in which the water is to be frozen, and a wire. With the quantity of ether contained in this small and very portable apparatus, the experiment may be repeated about ten times. A person who wishes to perform such experiments in hot climates, and in places where ice is not easily procured, requires only a larger bottle of ether besides the whole apparatus described above." Electricity increases the cold produced by means of evaporating ether but very little, though the effect is perceptible. Having thrown the electrified and also the unelectrified stream of ether upon the bulb of a thermometer, the mercury was brought down two degrees lower in the former than in the latter case.

Our author observes, for the sake of those who may be inclined to repeat this experiment, that a cork confines this volatile fluid much better than a glass stopple, which is almost impossible to grind with such exactness as to prevent entirely the evaporation of the ether. When a stopple, made very nicely out of an uniform and close piece of cork, which goes rather tight, is put upon a bottle of ether, the smell of that fluid cannot be perceived through it; but he never saw a glass stopple which could produce that effect. In this manner, ether, spirit of wine, or any other volatile fluid, may be preserved, which does not corrode cork by its fumes. When the stopple, however, is very often taken out, it becomes loose, as it will also do by long keeping; in either of which cases it must be changed.

Rink of the Ice, is a name given by the pilots to a bright appearance near the horizon occasioned by the ice, and observed before the ice itself is seen.

Ice-Boats, boats so constructed as to sail upon ice, and which are very common in Holland, particularly upon the river Maese and the lake Y. See Plate CCL. They go with incredible swiftness, sometimes so quick as to affect the breath, and are found very useful in conveying goods and passengers over lakes and great rivers in that country. Boats of different sizes are placed in a transverse form upon a 2½ or 3 inch deal board; at the extremity of each end are fixed irons, which turn up in the form of skids; upon this plank the boat rests, and the two ends seem as out-riggers to prevent oversetting; whence ropes are fastened that lead to the head of the mast in the nature of shrouds, and others passed through a block across the bowprit; the rudder is made somewhat like a hatchet with the head placed downward, which being pressed down, cuts the ice, and serves all the purposes of a rudder in the water, by enabling the helmsman to steer, tack, &c.

Method of making Ice-Cream. Take a sufficient quantity of cream, and, when it is to be mixed with raspberry, or currant, or pine, a quarter part as much of the juice or jam as of the cream; after beating and straining the mixture through a cloth, put it with a little juice of lemon into the mould, which is a pewter vessel, and varying in size and shape at pleasure; cover the mould and place it in a pan about two-thirds full of ice, into which two handfuls of salt have been thrown; turn the mould by the hand-held with a quick motion, to and fro, in the manner used for milling chocolate, for eight or ten minutes; then let it rest as long, and turn it again for the same time; and having left it to stand half an hour, it is fit to be turned out of the mould and to be sent to table. Lemon juice and sugar, and the juices of various kinds of fruits, are frozen without cream; and whea cream is used, it should be well mixed.

Ice-Hills, a sort of structure or contrivance common upon the river Neva at Peterburgh, and which afford a perpetual fund of amusement to the populace. They are constructed in the following manner. A scaffolding is raised upon the river about 30 feet in height, with a landing place on the top, the ascent to which is by a ladder. From this summit a sloping plain of boards, about four yards broad and 30 long, descends to the superficies of the river: it is supported by strong poles gradually decreasing in height, and its sides are defended by a parapet of planks. Upon these boards are laid laid square masses of ice about four inches thick, which being first smoothed with the axe and laid close to each other, are then sprinkled with water; by these means they coalesce, and, adhering to the boards, immediately form an inclined plain of pure ice. From the bottom of this plain the snow is cleared away for the length of 200 yards and the breadth of four, upon the level bed of the river; and the sides of this course, as well as the sides and top of the scaffolding, are ornamented with huts and pines. Each person, being provided with a sledge, mounts the ladder; and having attained the summit, he lets himself upon his sledge at the upper extremity of the inclined plain, down which he suffers it to glide with considerable rapidity, pushing it as he goes down; when the velocity acquired by the descent carries it above 100 yards upon the level ice of the river. At the end of this course, there is usually a similar ice-hill, nearly parallel to the former, which begins where the other ends; so that the person immediately mounts again, and in the same manner glides down the other inclined plain of ice. This diversion he repeats as often as he pleases. The boys also are continually employed in sliding down these hills; they glide chiefly upon one sledge, as they are able to poise themselves better upon one leg than upon two. These ice-hills exhibit a pleasing appearance upon the river, as well from the trees with which they are ornamented, as from the moving objects which at particular times of the day are descending without intermission.