EFFUSION (Lat. effusio, from flaw/ere, to pour out. from rx, out + prtiere, to pour). A term applied to the free outflowing of a gas through a pinhole, the resistance to the outflow being very small. The velocity of effusion is in the case of all kinds of gases found to lie in versely proportional In roots of ihrir densit irs, and this holds good under all possible circumstances. An increase of the pressure exer cised upon the gas has no effect on its rate of effusion. This appears somewhat strange on first thought; for it would seem that more gas should be expelled from a vessel by ine•eased pressure. It is clear, however, that this must necessarily be the ease, if we remember that when the pressure of a gas increases, its density inerea-es at precisely the same rate; an in crease of density causes a diminution of the rate of effusion. and thus the effeet of a greater ex pilling force is exactly counterbalanced; so that the amount of gas actually flowing out through the hole remains unchanged.
Quite different from illusion is the phenome non of Ironspirotion of yo.ses, i.e. the outflow of gases through long capillary tubes offering eon siderable resistance to their passage. The rate
of transpiration of a gas depends on font. tors: (1) the nature of the gas; (2) the density of the gas; (3) the pressure under which it is being expelled; and (4) the length of the tube. The first of these factors of course remains the same if one and the same gas is experimented upon under different. conditions. The rate of transpiration is then found to be ffireetty pro portional to the density as well as to the ex pelling pre-sure. and to be inversely proportional to time length of the tube.
The phenomena of effusion and transpiration are essentially different from those of diffusion. In the former the gases move in masses, in dif fusion they move by niolerules. See DIFFuskos, EFT, or EVET (AS. clete). A term formerly applied popularly and scientifically both to lizards and newts. It is now synonymous with newt, and in the United States red eft or evet is 'a local name of the spotted newt (Diemyrty Ins ininiains). See NEWT.