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Condenser. In Chemistry, a piece of apparatus employed for the purpose of condensing to the liquid state the volatile vapours evolved in distillation (q.v.). The most common and generally useful form is that known as Liebig's condenser, consisting of an inner glass tube surrounded by a larger outer tube, with a current of cold water kept flowing between the two. If very volatile liquids are being distilled it is frequently necessary to pass the gases through a spiral tube or "worm" surrounded by ice-cooled water or a mixture of ice and salt. Various complicated forms of condensers are sometimes eenployed, which serve also to partially separate the more volatile from the less volatile products of distillation. In the steam engine it is an arrangement for converting the exhaust steam into water, so as to diminish the back pressure in the cylinder to a much lower intensity than that of the atmosphere. Engines that do not employ such an arrangement are termed non-condensing engines, of which locomotives afford an illustration. Economy of space and weight may forbid their use, though with them the engines are more efficient. Condensers are of two types: - Jet condensers employ a jet or spray of water falling into a suitable chamber. The exhaust steam enters from the cylinder, and is at once condensed. It warms the water, but cannot return at any high temperature to the boiler again. Surface condensers consist of a series of communicating metal tubes into which the steam passes; the tubes are kept cold by water flowing round them on the outside. The condensed steam in this way does not mix with the condensing water, and may be pumped back into the boiler at a high temperature. This arrangement utilises a certain amount of heat, the same water is used continually, and very little sediment is deposited in the boiler. In Electrical Engineering it is an arrangement of two conductors separated by a non-conductor or dielectric. Thus a Leyden jar, consisting of a glass vessel coated inside and outside with tinfoil, or a submarine cable formed of a conducting wire insulated from the surrounding water by a guttapercha coating, affords an example of condenser. So also a thunder-cloud and the earth, with the non-conducting air between them, form a condenser. If a quantity of positive electricity be introduced on to one of the conductors, an equal quantity of negative electricity will be induced on the nearer side of the other conductor. If the two conductors are close together, the tendency for these opposite electricities to combine is almost permitted, and there is not much potential energy in the system; if the conductors are far apart and if they possess the same quantities of electricity as before, work has been done to separate them and the system is at a higher potential. So, in the former case, it will require a larger amount of electricity on the conductors to bring the potential energy up to the standard volt (q.v.). This amount of electricity is called the capacity of the condenser; it is measured theoretically in farads, commercially in millionths of a farad, or microfarads. If the dielectric is not sufficiently thick or strong, the tendency of the two electricities to combine will be great enough to break the dielectric - as for example in the lightning-flash which exhibits the disruption of the air-space between the cloud and the earth. Practically, the capacities of condensers are increased by making them of several pairs of plates instead of a single pair. The dielectric is chosen of paraffined paper or mica, to effect the same result. Their use in practice is very extended.