airproof (ar prof)

Impervious to air. air-pump (ar pump), n. An apparatus for the exhaustion, compre ion, or transmi ion of air. Air-pumps are used for many purposes, and are made in a variety of forms, which differ according to the uses that they serve. In the more common forms the air is exhausted by means of a cylinder and piston, as in Ritchie's air-pump (see cut), or by centrifugal action. Rotating buckets dipping into water, which forms a seal, are used for some special purposes; as is also, for slight changes of pre ure, a form consisting of a ve el closed at the top and sides but open at the bottom, and dipping to a certain extent into water or other fluid, which forms a seal and prevents the escape of the air. For the Sprengel airpump, see mercury air pump, under mercury. The air-pump of a condensing steam-engine is used to IMG:content-0450.png:[blocks in formation] air-sac (ar's ak), n. 1. In ornith., a large air-cell; an air-space, an air-receptacle, or a pneuma to cyst; one of the membranous bags or receptacles of air lodged in the hollow bones and the cavities of the body of birds, and communicating with the lungs.-2. pl. The elongated cavities forming the ultimate branches of the air-pa ages in the lungs of mammals. Also called infundibula.