Another substance, which is free from any corrosive action or unpleasant odour, is the nitrate of ammonia, which, if simply dissolved in rather less than its own weight of water, reduces the temperature to about twenty-five degrees below freezing. The objections to its use are, that its frigorific power is not sufficiently great to freeze readily;and if it is required to form dessert ices, it is requisite to renew the process at the expiration of a quarter of an hour, a second, or even, if the weather is very hot, and the water used is rather warm, a third or fourth time. Again, the nitrate of ammonia is a very expensive salt;even in France, where it is manufactured expressly for this purpose, it is sold at the rate of three francs a pound; and in this country it cannot be obtained under a much higher price. One great recommendation, however, attends its use, namely, that it may be recovered again, and used any number of times, by simply boiling away the water in which it is dissolved by a gentle fire, until a small portion, on being removed, crystallizes on cooling.

If, however, nitrate of ammonia in coarse powder is put into the cooler, and there is then added twice its weight of freshly-crushed washing soda, and an equal quantity of the coldest water that can be obtained, an intensely powerful frigorific mixture is the re sult, the cold often falling to forty degrees below freezing. This is by far the most efficacious freezing mixture that can be made without the use of ice or acids. But, unfortunately, it lt has an almost insuperable objection, that the nitrate of ammonia is decomposed by the soda, and cannot be recovered by evaporation;this rises the expense to so great a height, that the plan is practically useless

The New Freezing Preparation without Ice or Acids obviates all these objections. It is easy of use, not corrosive in its properties, and capable of being used at any time, at a minute's notice; is easy of transport, being in a solid form, and, moreover, moderate in its cost. In India, to which country it has been exported in enormous quantities, it has excited the most lively interest. It consists of two powders, the first of which is composed of one part by weight of muriate of ammonia, or sal-ammoniac powder, and intimately mixed with two parts by weight of nitrate of potash, or saltpetre. These quantities are almost exactly in (what is called by chemists) the combining proportions of the two salts, and by reacting on each other, the original compounds are destroyed, and in the place of muriate of ammonia and nitrate of potash, we have nitrate of ammonia and muriate of potash;thus we have succeeded in producing nitrate of ammonia at a cheap rate, accompanied by another salt, the muriate of potash,which also produces considerable cold when dissolved;but this mixture used alone cannot be regarded as a freezing one, although very efficient in cooling.

The other powder is formed simply of the best soda, crushed in a mortar, or by passing through a mill; although, as hitherto prepared, its appearance has been disguised by the admixture of small quantities of other materials, which have, however, tended to diminish its efficacy. The two powders so prepared must be separately kept in closely-covered vessels, and in as cool a place as possible; for if the crushed soda is exposed to the air,it loses the water it contains, and is considerably weakened in power; and if the other mixture is exposed, it, attracts moisture from the air, and dissolves in it - becoming useless. To use the mixture, take an equal bulk of the two powders, mix them together by stirring, and immediately introduce them into the ice-pail, or vessel in which they are to be dissolved, and pour on as much water (the coldest that can be obtained) as is sufficient to dissolve them;if a pint measure of each of the powders is used, they will require about a pint of water to dissolve them. More water than is necessary should not be used, as in that case the additional water is cooled instead of the substance that it is wished to freeze Less than a pint of each powder, and about the same quantity of water, will be found sufficient to ice two bottles of wine, one after the other, in the hottest of weather, if a tub is used of such a size as to prevent the waste of materials.

If the ordinary sal-ammoniac of the shops is used, it will be found both difficult to powder, and expensive;in fact, it is so exceedingly tough, that the only way in which it can be easily divided, except in a drug mill, is by putting as large a quantity of the salt into water which is actually boiling as the latter will dissolve; as the solution cools, the salt crystallizes out in the solid form, and if stirred as it cools, it separates in a state of fine division. As thiss process is troublesome, and as the sal-ammoniac is expensive, it is better to use the crude muriate of ammonia, which is the same substance as sal-ammoniac, but before it has been purified by sublimation. This is not usually kept by druggists, but may be readily obtained of any of the artificial manure merchants, at a very moderate rate; and its purity may be readily tested by placing a portion of it on a red-hot iron, when it should fly off in a vapour, leaving scarcely any residue.

It is hardly necessary to add, that in icing wines, or freezing, the effect is great in proportion to the coldness of the materials used; therefore, every article employed, viz., the water, tubs mixtures, etc., should be as cool as possible.