Page:The New International Encyclopædia 1st ed. v. 01.djvu/189

AËRATED WATERS. sively WicA to qupiuli tliii<t. and are commonly called soda waters. The <arli(Piiio acid used in making the common artificial ai'ratcd waters is prepared by trcatinj: a mineral carbonate, as chalk or liine-stonc, with dilute snli)luiric acid. The gas thus obtained is forced into bottles or siphons containini; water. yicldin<r a brisk, sparkling liciuid with a pungent but pleasant acidulous taste. Artificial waters, similar to seltzers, vichy, and other well known mineral waters, are produced by dissolving the known ingredients of the mineral water in distilled water and then im])rcgnating them with carbon dioxide gas. The carbonic acid water mixed with fruit syrups is the ordinary soda water of the pharmacy. Formerly carbonic acid water was made on a small scale in an apparatus called a gazogene or seltzogene {see accompanying figure), in which sodium bicarbonate was decom- posed by tartaric acid in the presence of water. A recent invention is the use of capsules contain- ing liquefied carbon dioxide. The liquid which it is desired to impregnate with the gas is placed in a specially constructed bottle, the top of which is provided w-ith a receptacle for the capsule containing the liquefied gas: the covering of the capsule is then ruptured, setting free the acid, which is absorbed by the liquid in the bottle. Aerated waters may also be said to occur natu- rally, for water taken from a spring contains gases, such as oxygen, nitrogen, and carbon diox- ide, dissolved in it. Similarly, running waters, such as rivers and rain waters, absorb gases from the atmosphere, which may be expelled by boiling. See A Treatise on Bereruf/es, by C. H. Sulz, and the articles, Carboxateu or Acid- irLOu.s Wateks, and JIineral Waters.

A'ËRA'TION (Lat. aer, air). In botany, the cxcliaiigc of gases between living plant tissue and the surrounding medium. This exchange is manifested by two processes. In one of these, viz., the manufacture of certain foods (see PliOTOSY.NTiiEsls), carbon dioxide is required by the plant and oxygen must be eliminated. On the contrary, in the other process, viz., respira- tion (q.v.), oxygen is necessary and carbon diox- ide must be eliminated. The former process is confined to giecn jplants: the latter is essential to all excc]>t a few of the lowest and simplest type (anaerobic bacteria). Among the smaller plants, and those whose bodies are made ip of interwoven filaments (Fungi), the gaseous ex- changes can take place directly, since almost every part of the body is in contact with the air or with water. In the former case, the outside gases dissolve in the constituent water of the cell-wall and are then free to enter; or, arising within the cell, and being already dissolved, they pass ofl' into the air. In water plants the free inward or outward migration of dis- solved gases depends on the relative amounts inside and outside the body. (See Absorption.) In the larger land plants the greater number of cells and the more compact structure make it impossible for the cells more distant from the surface to conduct the necessary changes at an adequate rate. Such plants have therefore devel- oped an extensive aerating system (fig. 1), con-

Diagraninintic cross-section of a leaf, showing the iniercellnlnr spaces in the interior, i, and in tlic epi- dermis t= gtomata), a.

sisting of irregular passages, i, between the inte- rior cells, which communicate with the outer air through microscopic openings, ,«, between the sur- face cells ( see Stomata ), or through larger breaks in the coiky layers of tissue on the surface of the stems. { See Lenticels. ) The intercellular pas-

Pan of a cross-section of the root of Jnssia?a. show- ing acrcncliyma, witll cllornious inliTcellLilar spaces, the cells hi'ing a mere scutToUling between the surface (not shown) and the central cylinder (at the lower margin).

sages and stomata are formed by the partial separation of the cells as they mature. In land