Page:The New International Encyclopædia 1st ed. v. 01.djvu/80

ABSORPTION. able mainly on this basis. Thus, wheat and clovei- may grow side by side; the ash of the wheat will contain 7.5% of silica, while that of the clover cojitains only 2.5%. This selective absorption must, however, be in part referred to the power pos.sessed by protoplasm of regulat- ing the admission of solutes.

(2) Water. Entrance of water into the plant to supply losses by evaporation or consumption depends upon similar factors. In a living mature cell, the protoplasm usually lies in a thin layer close to the cell-wall and envelops a water-filled space, the vacuole. (See Growth.) Many substances are constructed by plants which cannot ordinarily pass through the protoplasm, and remain dissolved in the water of the vacuole or cell-sap. These substances exert upon the surrounding layer of protoplasm a definite pres- sure. If tney were in gaseous form this would be their gas pressure. As the}' are dissolved, it is called their osmotic pressure. The osmotic pressure of solutes in the water outside the plant is usually less than that of solutes in the cell-sap. As the solvent moves towaril the region of higher osmotic pressure, i.e., from a place where there is a greater number of water molecules in unit-space, to a place where there are fewer, water usually enters the plant. But if at any time the conditions are reversed, the solutes outside the plant having higher osmotic pressure than those inside, water will leave the plant. This happens in nature sometimes, and it is this condition that makes possible the destruction of weeds by common salt. Gases are absorbed in the same manner as solids ; the a])parent difl'erence in their absorption by land plants is due tti the fact that they mostly become dissolved (and so fitted for absorption) only when they come into contact with the water saturating the cell-wall. This condition among the larger land plants exists only in the walls of cells bordering intercellular spaces. ( See Ai:R.Tiox.) While land plants absorb gases chiefly from the atmosphere, doubtless some ab- sorb them by the roots, notably the oxygen re- quired for their own respiration.

ABSORPTION, Klectrical. A phenomenon observed in electrical condensers (q.v. ), in which the dielectric or insulating material between the conductors is non-homogeneous, e.g., a piece of glass. It is noted that if such a condenser is charged, then discharged and allowed to stand for a short time, there will appear another charge. If this is discharged, another charge will soon appear. These secondary charges are said to be due to electrical absorption. See Electricity.

ABSORPTION OF Gases. The phenom- enon of the taking up or absorbing of gases by liquids and solids. Tiie number of cubic centi- meters of a gas which can be absorbed by one cubic centimeter of a given liquid at 1.5° C. is called the "absorption coeflicient" of the liquid for the gas. The absoiption coefficient of water for ammonia is T.'iO: for carbon dioxide, 1.0; for chlorine, 2.4. The mass of the gas absorbed varies directly as the jjressure: so, if a gas is forced into a liquid under high pressure, and if the pressure is afterward released, the gas will be evolved. This is what ha])pens in the case of beer and aerated waters. The .ibsor))tion of gases by solids is called occlusion. The most conspicuous illustration of this is the power of palladium to occlude nine hundred times its own volume of hydrogen.

ABSORPTION OF Waves. Waves of any kind in any medium carry energy with them; and, if the energy decreases, the medium is said to absorb it or to exhibit "absorption." Thus, if white light falls upon red glass, i.e., if ether- waves which affect the normal luiman eye with the sensation "white" are incident upon glass which appears red to the same eye, all the waves except those which produce the sensation red are absorbed by tk2 glass, while the others are transmitted. ISodies differ greatly in the qual- ity and quantity of their absorptive power ; bvit it is a general law that the absorptive power of a body equals its emissive power under the same conditions. (See Kahiation.) Absorption is due to the presence in the pure medium carrying the waves of some portions of matter whose own natural period of vibration is the same as that of the period of the waves; and. therefore, these portions of matter are set in vibration by "reso- nance" ( q.v. ). Thus, if a person sings a pure note near a piano it may be observed that the particular string of the piano which of itself gives the same note is set in vibration by the air-waves sent out by the singer. If air-waves of any length fall upon a soft bod}', such as a cushion or a curtain, there is absorption, as is shown bj' the fact that the re- flected waves are nuich less intense than the incident waves. The energy thus absorbed is not spent in emitting other waves, but is dis- sipated throughout the body producing heat effects. Similarly, if ether-waves fall upon an absorbing body, the energy absorbed is dissi- pated in general throughout the smallest par- ticles of the body producing heat effects. See, however. Fluorescence.

AB'STINENCE. See Past.

AB'STINENCE SOCFETIES. Associations to iiromotc total abstinence from alcoholic liquors as beverages. See Temperance.

ABSTRACTION (Lat. a 6s, away -f trahere, to draw). In logic, the jirocess by which the mind separates out marks or characteristics which are similar in various objects, and disre- gards the marks or characteristics by which the objects differ. It also occurs where characteris- tics of particular objects, or classes of objects, are replaced by a more general characteristic. An instance of the first kind is the formation of the class "biped" by the inclusion of all two- legged animals. An instance of the second type is the substitution of the general mark "repro- duction" for the more special marks, "vivipa- rous," "oviparous," "fissipaious," etc. The re- sult of this process is also called an abstraction, or, if it appears as a word, a concept. The psy- chology of abstraction consists in describing the way in which the attention, in passing from one object to another, fastens upon an element com- mon to all and dissociates it from its context. Abstraction is carried out in a state of active attention (see Attention ), as when the phi- lologist searches out common or allied roots in different languages, or when the geologist iden- tifies strata in different localities and forms the abstraction of a single ei)och in which they were laid. The process is, however, facilitated by the sheer decay of mental complexes; a decay which obliterates small differences and reduces mere similarity to indistinguishableness. It this comes about that we form sketchy, "ab- stract" images — as of "pen," "house," or "book"