There are now about forty different styles of ice-machines in operation in different parts of the world, Nearly a hundred have been patented at Washington. Not over half a dozen, however, are in this  country considered of much practical value at the present time. The machines are all the same in principle, though various in construction. The principle is that a liquid in changing its form to a vapor abstracts beat from all surrounding substances; the more rapid the evaporation the more intense being the cold produced. The chief troubles the inventors have encountered have been the danger of explosion, to which the ether machine is especially liable; the leakage of the gases through the joints and pumps, which, by diminishing the pressure within, destroys the efficiency of the machine; the fact that an invention which will work successfully in a northern climate sometimes proves a failure in a warmer region, and the frequent great cost of operation. In order to carry on a successful business in artificial ice-making the product must be manufactured at a cost of not to exceed $2 or $3 a ton. The chief cause of the numerous disastrous failures so far has been that the product cost anywhere from $20 to $250 a ton. One American proprietor lost $100,000 in experiments at New Orleans before success was achieved. It has been the aim of inventors in this country to make ice at from 75 cents to $1 per ton. Many times during the last ten years the announcement has been made that the result has been accomplished. It is doubtful if, in practice, any ice-maker in America has yet been able to produce ice so cheaply; but the cost has, nevertheless, been reduced at length to a point where the making of ice is commercially practicable, and it is now carried on as a regular industry in a large number of southern cities in competition with the importation of natural ice from the north.

The process of ice-making is substantially the same in all machines, and a description of the way the thing is done by the Louisiana Ice Manufacturing Company of New Orleans will give a correct notion of it. The substance employed for evaporation is ammonia. In its uncombined form ammonia is a gas, having a remarkable affinity for wafer. A compound of water and ammonia is placed in an iron retort, or boiler, the fluid being deep enough to cover a coil of pipe in the bottom of the retort, occupying about one-third of its capacity. A current of steam is sent through this coil to heat the water to from 1300 to 1500, and to volatilize the ammonia. The heat disengages the gas, which rises into the top of the retort, and is carried off into a series of pipes in a square box, called the “liquidator." Cold water circulates in a constant current around the pipes of the liquidator, and the gas condenses to a liquid under the influences of the refrigeration it receives and the pressure of the new gas which is continually coming. The liquid ammonia flows into a reservoir below called the "recipient" until a sufficient quantity has accumulated to begin the work of making ice. It is the return of this liquid to its gaseous form, or, in other words, its evaporation when pressure is removed, that generates the ice. A stopcock is opened which allows the ammonia to flow from the recipient into and through a network of pipes which fill the interior of a large tank called the "refrigerator." Finding room for expansion, the ammonia rushes into the pipes, vaporizes, absorbs heat in the process from the salt water surrounding the pipes, and rapidly reduces the temperature of the brine much below the freezing point. The brine, thus suddenly cooled, in turn absorbs beat from shallow pans of fresh water which are suspended in the refrigerator, and the fresh water is converted into blocks of solid ice. If this were the end of the process ice-making would be too expensive for commercial success. But so far only one-half of the business of the machine has been performed. The next step is to recover the gaseous ammonia for use it second time. When the ammonia was volatilized in the retort by heat a great pressure was generated. The water was forced back out of the bottom of the retort through a tube into an exchange or drum near by, and thence into it cooler, and still on into a "vase of absorption." Here the cooled water meets the gaseous ammonia, which has gone on through the refrigerator and has been conducted through tubes to the vase of absorption. The ammonia combines by affinity with the water again, forming a new saturated solution, and this is pumped back into the retort to undergo another operation. The gas, is thus, used over and over again. It is this part of the process which secures the economy of ice-making. This machine will make an average of 18 to 19 tons of ice a day, or about 5,500 tons a year.

Another variety of ammonia machine is used by the New Orleans Ice Manufacturing Company. It is the California invention of Mr. Beath. The principle is in all respects the same, but the ice is made not by freezing it in pans, but allowing it to form on the pipes of the refrigerating tank. The pipes are vertical, 32 feet high, placed in rows 4 feet apart one way, and 2 feet apart the other. When the liquid ammonia is allowed to enter them and evaporate into gas, water is showered upon the pipes and the ice forms on their surface, growing continually in thickness as long as evaporation continues. Water is thrown upon the pipes greatly in excess of the quantity that can be frozen. The result is that any solid substances contained in the water are washed down by the current, and thus the muddy water of the Mississippi river yields a pure and brilliant ice. The columns of ice around the pipes grow in diameter until they meet. They finally become transformed into perpendicular walls of solid ice, 32 feet high, and about 3 feet thick. Freezing is then stopped; gaseous ammonia is forced back into the pipes under pressure. Under compression heat is given out and the ice is melted away from immediate contact with the pipes. Horizontal and vertical grooves are then cut in the walls of ice and the blocks are split out and carried away for consumption. The house of the New Orleans company is large enough to hold 10,000 tons of ice. It is divided into four compartments, in which the vertical iron pipes are erected. In the winter of 7882-'83, with only half its apparatus hi use, the product was 50 tons a day.

Other machines have been tried in America, in which sulfurous acid and other liquids have been volatilized by creating a vacuum with a powerful pump, the liquid afterward being condensed under pressure. Two of the Roach line of steamers to Brazil were supplied with refrigerating apparatus of this class. The work done did not yield satisfactory results, and the machines were taken out. Inventions of this class are being used, however, in various parts of the United States.

Within a few years a class of machines has been brought out, intended not for the manufacture of ice, but for the refrigeration of storage rooms by cooling the air. They are ammonia machines, as a rule, and in large establishments have been found to give satisfaction. They have been introduced to breweries in large numbers within the last five years. There are those who now predict their universal adoption by brewers within the -next ten years, at least by all the large firms. It will be cheaper for the smaller firms to buy natural ice. A year of short supply and high prices tends to increase greatly the number of machines iii the breweries of the large firms.