Ice concretes generally on the surface of water; but this effect frequently varies under different circumstances. In the northern parts of Europe, there are three species of ice: 1. That which is formed on the surface. 2. Another kind, which congeals in the middle of the water, and bears some resemblance to small hail ; and, 3. Ground-ice, that is produced at the bottom; especially where it meets with any fibrous stance to which it may adhere. line last species is full of irregular ells ; and, on account of its inferior specific gravity, it produces many singular effects, by bringing up heavy bodies from the bottom of the water in which it is formed. The ice that concretes in the middle of the water, rises to the top, where it unites into large masses : the formation, however, both of this, and of the ground-ice, takes place only during intense and sudden frosts, in shallow waters, the surface of which is disturbed either by the wind or the current of a stream, so that it cannot be easily consolidated.
In many countries, the warmth of the climate renders ice not only a desirable, but even a necessary article: hence it becomes an object of some importance to procure it in a cheap and easy manner.— For this purpose, in the East Indies, three or four pits are dug on a large open plain, each of which is about thirty feet square, and two feet deep; the bottoms are covered to the depth of eight or ten inches with dried straw, or the stems of sugar-canes. On this bed are arranged, in rows, a number of unglazed pans made of porous earth, about a quarter of an inch thick, and an inch and a quarter deep, which are filled about sun-set, with water that has been boiled and become cool.— Early in the morning, a coat of ice is found on the pans, which is broken by striking an iron hook into its centre, and then conveyed in baskets to the place of preservation.
The most expeditious method, however, of producing ice, consists in a combination of sal ammoniac with nitre. It was first discovered by Boerhaave, whose experiments were repeated and confirmed by Mr. Walker, apothecary to the Radcliffe. Infirmary, Oxford; but he found that his thermometer sunk 32° in a solution of sal ammoniac, when Boer-haave's fell only 28° : nitre alone reduced it to 190. On mixing the two salts, in equal proportions, the power of generating cold was considerably increased ; so that the water was cooled to 22, while the thermometer stood at 47° in the open air. By adding some powder of the same composition, and immersing in the mixture two small phials rilled with water, he found it in a short time frozen.
Having observed that Glauber s salt, when it retains the water of crystallization, produces cold in a state of solution, Mr. Walker made an experiment of its effects when mixed with the other salts' before mentioned ; in consequence of which the. thermometer sunk from 69 to 190, and he obtained ice, while the thermometer stood as high as 700 - Lastly, by previously immersing the salts in the water of one mixture, and then making another of the cooled materials, he was able to sink the-mercury in the thermometer to 64. Thus, he froze a mixture of spirit of wine and water, in the proportion of seven of the latter to one of the former ; and, by adding. a quantity of the cooled materials to the mixture in which this was frozen, the quick-silver fell to the extraordinary depth of 69 degrees.
Various other methods of procuring artificial ice have been contrived, particularly by the aid of aether ; but that volatile spirit is too expensive for domestic purposes, and a satisfactory account of the process would exceed our limits.
Ice has lately also been introduced into medicine; and its external application was attended with success in various disorders, especially in typhus fever, acute rheumatism, strangulated ruptures, and chronic inflammations of the eyes, after proper evacuations had preceded. It has likewise been advantageously employed for re moving a retention of urine; and an instance lately occurred, in which a person was effectually re-lieved., by immersing his legs for five minutes in a pailful of ice and water taken fresh from the river. At first, it occasioned intense pain, but in a few minutes after the pa-tient had retired to bed, his complaint was alleviated ; and, in the course of twelve hours, he was perfectly restored. - Such a powerful remedy, however, should be re-sorted to only under medical su-perintendance.
Ice-cream, is prepared by mixing three parts of cream with one part of the juice or jam of raspberries, currants, etc. The mixture is then well beaten; and, after being strained through a cloth, is poured into a pewter mould or vessel, adding a small quantity of lemon-juice. The mould is now covered, and plunged in a pail about two-thirds full of ice, into which two handfuls of salt should be previously scattered. The vessel containing the cream is then briskly agitated for eight or ten minutes, after which it is suffered to stand for a similar space of time; the agitation is then repeated, and the cream allowed to subside for half an hour, when it is taken out of the mould, and sent to table.
Ice-house, a repository for the preservation of ice during the summer months.
The situation of an ice-house ought to be towards the south-east, on account of the advantage of the morning sun in expelling the damp air, which is far more prejudicial to it than warmth. The best soil on which such a house can be erected, is a chalk-hill, or declivity, as it will conduct the waste water, withou the aid of any artificial drain ; but where such land cannot be pro-cured, a loose stony earth, or gravelly soil on a descent, is preferable to any other.
For the construction of an ice-house, a spot should be selected -at a convenient distance from the dwelling-house. . A cavity is then to be dug in the form of an inverted cone, the bottom being concave, so as to form a reservoir for the reception of waste water. Should the soil render it necessary to con-struct a drain, it will be advisable to extend it to a considerable length, or, at least, so far as to open at the side of the hill or declivity,. or into a well. An air-trap should likewise be formed in the drain, by sinking the latter so much lower in that opening as it is high, and by fixing a partition from the top, for the depth of an inch or two into the water of the drain, by which means the air will be completely excluded from the well. A sufficient number of brick-piers must now be formed in the sides of the ice-house, for the support of a cart-wheel, winch should be laid with its convex side upwards, for the purpose of receiving the ice ; and which ought to be covered with hurdles and straw, to afford a drain for the melted ice.
The sides and dome of the cone should be about nine inches thick, the former being constructed' of steened brick-work, that is, without mortar, and with the bricks placed at right angles to the face of the work. The vacant space behind ought to be filled up with gravel, or loose stones, in order that the water oozing through the sides may the more easily be con-dueled into the well. The doors of the icc-house should likewise be so formed as to shut closely; and bundles of straw ought always to be placed before the inner door, for the more effectual exclusion of air.
The ice to be deposited in this building, should be collected during the frost; broken into small pieces ; and properly rammed down, in strata of about one foot thick, so that it may become one complete body: - in those seasons when sufficient quantities of ice cannot be procured, snow may be substituted, and preserved in a similar manner.