REFRIGERATING ffiACHINES. Under the head ICE, some notice is given of machines by which it can be prepared but tis the practical importance of refrigerating apparatus is daily increasing, we propose to give here a fuller sketch of one or two kinds. The ice making machine of Carre & Co. of Paris being the simplest and best of those which produce cold by the evaporation of some volatile liquid, we shall describe it first. It is shown in figs. 1 and 2, and consists of two strong cast iron cylinders A and B, connected together by a metal tube T, all perfectly gas-tight. The whole apparatus is made strong enough to stand seven or eight atmospheres of internal pressure.
The cylinder A is charged with an aqueous solu tion of ammoniacal gas. Ammonia is a powerful absorber of heat, and is, moreover, so extremely soluble in water that the latter takes up nearly seven hundred times its volume of the gas. Air is com pletely expelled from the apparatus by opening a screw valve and heating the cylinder. It is then ready for use. On applying heat to the cylinder A, which fits into a small stove for the purpose, the solution of ammonia is volatilized, and carried over and condensed in the cylinder B, which is placed in a vessel containing cold water. The heat reaches to about 220° Fahr., and while it is being applied, the volatilized ammonia condenses into a liquid under very high pressure, produced by its own atmosphere, in the cold cylinder B. When the heating has gone on long enough—about half an hour for a small ma chine—the hot cylinder A is removed from the fire, and placed in a vessel of cold water, as shown in lig. 1. The cooling of this cylinder immediately causes the reabsorption, by the removal of the pressure. of the condensed ammonia from the other cylinder 13; and as it passes again from the liquid to the gaseous state, intense cold is produced (see HEAT), and, in consequence, heat abstracted from every thing in contact with this portion of the apparatus.
The cold cylinder B is shown in section in fig. 1. It is so constructed that the ammonia is contained in an outer jacket, leaving a hollow space in the center. When
ice is to lie made the latter is filled with salt water or other liquid which does not freeze at 32° Fahr., and into this is placed a loosely fitting metal cylinder D, containing the water to be frozen. In this way, with a small machine for domestic purposes, a few pounds of ice can be made in an hour or two; but large machines, on the same principle, are made which produce 440 lbs. of.ice per hour.
There is a well-known refrigerating machine by Mr. D. Siebe of London, in which ether is used as the volatile fluid, its evaporation being produced not by beat, but by the action of an air-pump; the necessary cold is produced in the surrounding brine as the ether passes into vapor.
31. I'ictet of Geneva has invented an ice-machine which works with anhydrous sul phurous acid instead of ether; but otherwise his process somewhat resembles Siebe's. It is now at work at an ice-making company's works in King's road, Chelsea. Some ma chines are also in use which produce ice by means of freezing mixtures; but they•are of minor importance.
Mr. A. C. Kirk, late of the Bathgate chemical works, undertook, a few years ago, a series of experiments with a view to the construction of such an apparatus which would produce cold by the simple expansion and compression of air. He ultimately succeeded in producing an ingenious machine, which he patented April 25, 1862, the number of the specification being 1218.
Although it is not strictly true that the mere rarefaction of air produces cold, yet it will simplify the explanation of this machine to assume in the mean time that it does so. Its simplest form is shown in fig. 2, and consists of a cylinder with a piston to compress air, communicating with another cylinder containing a kind of piston or plunger where the compressed air is cooled and expanded. The machine is driven by a steam-engine, and it may be as well to remark, that the actual relative position of the cylinders is different from that shown in the diagram, which is given rather to show the principle of the apparatus than as an accurate representation of it.