The "binary absorption" system of Tessie du Mothay and A. I. Rossi is one of the most recent developments of the science of producing artificial cold. Experiments on ethers indicated that those formed by the acids, as well as their alcoholic radicals, possess the property of absorbing sulphurous anhydride (sulphur oxide), some of them to the extent of 300 times their volume of gas, in certain conditions, ordinary ether standing first. Upon this fact, the system is founded. The liquid employed is ethylo-sulphurous dioxide, obtained from ordinary ether by saturating with sulphurous oxide gas. This liquid, at a temperature of 60°-65° F. (15°-18° C), has no pressure, and can be readily kept in glass bottles at 80°-90° F. (27°-32° C); its tension is only 2-5 lb. Thus a machine charged with it, when stopped, will show no pressure on the gauges, and even a vacuum at rest, if the temperature is low; while with other liquids, even the stoppage of the machine does not prevent the pressure of the vapours inside soon reaching its point of equilibrium with the temperature outside, and even at as low a temperature as 32° F. (0° C.) sulphur dioxide (sulphurous oxide) alone, as used in the Pictet machine, has still 15 lb. a sq. in. of pressure, exerting a constant and increasing pressure on the vessels containing it, and, in case of a small leak starting, causing the entire loss of the charge.
Such a binary liquid as that just mentioned, when evaporated under a vacuum, is resolved into its two constituents, the mixed vapours entering the pump together; then, under a small compression, ether liquefies first, a few lb. pressure being sufficient for it, even with such waters as are met with in tropical climates. The ether thus liquefied absorbs in the condenser the vapours of sulphurous oxide, reconstituting the "binary liquid," and thereby avoiding the excess of mechanical compression, which would otherwise have been necessary to effect this liquefaction of the oxide. Thus, for the work of compression of the pump, is substituted a power of chemical affinity, and absorption of the less volatile absorbent for the vapours of the more volatile. With the advantage of the low pressure of the ether, is combined the advantage of the intensity of cold produced by the volatilisation of the sulphurous oxide, avoiding its drawbacks. In presence of water and the ether, the sulphurous oxide is transformed, not into sulphuric acid, as before, but into "sulphorinic" acid, the action of which acid upon metals is insignificant, if not absolutely nil.
The sulphurous acid being an ex-tinctor, relieves the ether of one of the drawbacks to its use, and acting as self-lubricant, renders the greasing of the working parts unnecessary. In a machine making 6 tons of ice daily, the pressures in the condenser in normal and regular working have been 14-15 lb., descending to 10-11 1b. under most favourable conditions, and reaching 20-23 lb. under least favourable conditions. The water used for condensation has been but 1/4 to 1/4 of that needed by a Pictet machine of the same capacity. The smallness of pressure required renders the machine much simpler, ordinary valves, etc, sufficing. The New York Ice Machine Co. are working very successfully with the system in the United States.
Recently Rossi and Beckwith have discovered that still better effects are and glycerine. The non-volatile glycerine absorbs at low pressure many volumes of ammonia; and when the ammonia is vaporised by the action of a pump, intense cold is produced. The chief advantage claimed for the new compound arises from the utilisation of the great cold-producing power of neutralisation of its enormous pressure by its absorption in the glycerine. When the machine is at rest, the pressure is from zero to 15 lb., as against 125 lb. in the ordinary ammonia machine; and when the machine is at work, the pressure is 35 to 50 lb. as compared with a pressure of 225 to 300 lb. in the ammonia machine.
Sulphuric acid is the medium employed in Carre's domestic apparatus shown in Fig. 20. It consists of a large vessel a for holding the concentrated sulphuric acid; an air-pump p, with tube connections r, adapted to the mouths of the decanters f; and a mechanism by which the lever h of the air-pump keeps the acid in continual motion; l is a stop-cock. This apparatus is useful for cooling drinks.
Pictct's machine shown in Fig. 21 is intended more especially for domestic use, about 2 lb. of ice being produced In 10 minutes with the minimum of vaporises. The apparatus is composed, as usual, of a freezer, a compressing pump, a condenser, and a distributor working under the ordinary conditions; but the freezer has peculiar arrangements for constantly supplying the loss, which however is very slight, of volatile liquid, and so the apparatus remains ready for work without any fresh supply for a long time, any, for example, a year. The freezer consists of 2 superposed chambers, of which the lower is the refrigerator properly so called, working between 'A levels very close together, and of which the upper chamber is the provision made for reserve. The refrigerator consists of a cylindrical receiver A, within which an annular vessel B is formed, and from the centre thereof a column C springs, it communicates with the receiver and is swelled out at the top, forming an enlargement D furnished with stop-cock £ having a nozele G. The receiver has on its side a small passage F. The apparatus is charged by introducing the volatile liquid by G to fill the whole interior capacity of the refrigerator A to the top of the column C, where it is terminated by the stop-cock £; this forms the charge of the apparatus.
When the distributing cock is adjusted, which puts the refrigerator in communication with the condenser, all the excess of volatile liquid above the orifice of the pipe F runs into the condenser to the level indicated by the line a a. The liquid evaporating from all its free surface, it is necessary to ensure constant equilibrium between the enclosed part of the receiver and the interior of the column C by means of one or more curved tubes of U form, as indicated. The vessel B receives 3 conical annular moulds filled with water to be frozen; they fit almost exactly against the sides of the vessel B - which, however, contains, as is usual, a small quantity of uncongealable liquid, such as glycerine, to ensure the interchange of temperature. When the ice is formed, the moulds are taken out and treated in the usual way to remove the ice. The abstraction of heat necessary to freeze the water in the moulds corresponds to the evaporation of a weight of volatile liquid equal to the difference between the original level a a and the level b b to which it descends after the freezing. The refrigerator is completely enveloped in a wooden case packed with cork dust to ensure its isolation.