that had previously hindered successful working. The inflammability of ether was nullified by the sulphurous acid; a perfect lubricant was obtained, and the substance had no corrosive action on the metals employed. But the most interesting feature developed by the experiment was that the ether was found to have the power of absorbing a large proportion of the gas of the sulphurous acid. This is the characteristic feature of the binary absorption system, as Du Motay termed his process. The ether, by absorbing the gas of the other constituent liquid, reduces the mechanical problem to that of liquefying a gas having a pressure not approximating that of sulphurous acid, viz., fifty to eighty pounds or more per square inch, but barely more than that of ether itself, viz., twenty pounds. The pressure of the compound at rest, like that of ether, is nil. In other words, the ether is found to have accomplished the greater part of the work, and a law of nature governing the action of certain chemicals in combination is availed of to reduce the mechanical labor of liquefaction to a minimum.
Since the death of Du Motay, which occurred very soon after his discovery, his associates, MM. Auguste Rossi and Leonard F. Beckwith, have continued the experiments under the Du Motay patents, with various other compounds, and have accomplished the hitherto unheard-of result of liquefying ammonia gas in the pump at a pressure of thirty-five pounds per square inch. This is accomplished by combining it with glycerine, a non-volatile, which gives up the ammonia gas in the vacuum-pump, but, when it has reached a certain tension, seizes it, so to speak, and renders it liquefiable at a fraction of its ordinary pressure.
There are various other compounds capable of giving the same results—an intense freezing power at a greatly diminished pressure, and the peculiarities of various industries employing mechanical refrigerants can thus be consulted and met by the use of whatever compound is found best adapted thereto.
There are certain general features common to all the systems employing a liquid volatilizable in the vacuum-pump, but the peculiar features of the binary absorption process admit of such a simplifying of the mechanical appliances employed as to materially distinguish their construction from that of other systems.
The freezing agent, ethylo-sulphurous dioxide, or glycerine and ammonia, or whatever be the compound employed, is placed within the "refrigerator," which consists of tubular coils immersed in an un congealable mixture. A double-acting vacuum-pump volatilizes the agent in the refrigerator coils, and this is attended with the development of an intense cold, which is communicated to the surrounding mixture, and the latter, by means of a circulating pump, is made to flow through a suitable tank containing vessels of water to be frozen, or, if air-cooling only be desired, through iron tubing placed along the
