EXOSMOSK 



... The explanation given. by this excellent authority has beon selected as representing 

 fairly tlio prevailing" view. It is not, how.v.T. Bfttufeotoiy. The water is said to bo 

 at a sensible distance from the hot plate, and a layer of aqueous vapour of very high 

 temperature is known to surround the water, and yet the spheroidal water does not 

 acquire the boiling temperature. Here is evidence of some peculiar, and as yet un- 

 explained condition, belonging, either to heat of a certain kind or degree, or to the 

 molecules of the body under its influence. 



Boutigny observed that water may pass into the spJieroidal state when projected 

 xipon metal above the temperatures of 142. Ether and alcohol pass into the spJieroidal 

 state between the temperatures 142 F. and 273 F. A thermometer being plunged in 

 liquids while in the spheroidal state, indicated the following temperatures : 



Water 205'7 F. 



Absolute alcohol 167*9 



Ether 93-6 



Hydrochloric ether 50'9 



Sulphurous acid 13'1 



All these being some degrees below the boiling temperature of those fluids. 



Boutigny has shown that the vapour escaping from water in the spheroidal state, 

 although it has a very elevated temperature, does not possess the usual elasticity of 

 steam ; it does not exert an expansive power. But if the vessel from which the 

 vapour is forming is allowed to cool, to a certain point, a degree of elasticity equal to 

 the elevated temperature of the vapour is suddenly exerted. This is supposed by 

 Boutigny to explain many steam-boiler explosions. 



Whenever evaporation takes place, it should be remembered, it produces cold 

 that is, it lowers the temperature of the body from which the evaporation is taking 

 place. Leslie, by the evaporation of ether in vamo, froze mercury. Thilorier solidi- 

 fied carbonic acid by the intense cold produced by its own evaporation. Boutigny 

 froze water in a red-hot vessel, by the evaporation of sulphurous acid from the heated 

 vessel in which the water is in the spheroidal state. Faraday froze mercury in a red- 

 hot crucible by the evaporation of a mixture of solid carbonic acid and ether. But 

 the lowest temperature yet reached has been in the experiments of Natterer, of Vienna, 

 who obtained as low a temperature as 220 F. by mixing liquid nitrous oxide with 

 bisulphide of carbon, and evaporating this mixture in vacuo. Carre's freezing-machine 

 depends for its action on the rapid evaporation of a solution of ammonia. 



The spheroidal condition of fluids does not appear to be dependent entirely on heat. 

 By dropping alcohol or ether on the surface of the same fluids, such spheroidal drops 

 may be obtained ; and water splashed upon water often assumes the same condition. 

 Mr. Tomlinson has some curious experiments upon the formation of these varieties of 

 spheroids. 



Further remarks on these points will be found under the heads respectively of 

 COAL ; FKEEZIXG ; and VAPOUB. See also HEAT, in Watts' s ' Dictionary of Chemistry. 1 



EVSHI.ASTIWG FLOWERS. These dried flowers, largely used by the 

 French as Immortelles, are for the most part species of Gnaphalium, Helichri/sum, and 

 other plants of the natural order Composite. 



EVERNIC ACID. An acid extracted from the lichen Evernia prunastri. 



EXAIVTHXNZ:. The Purree or Indian yellow of India. See INDIAN YELLOW. 



EXOGENS. A botanical term, applied to plants which grow by addition to the 

 outer parts of the stem. Most British trees are Exogens. The correlative term En- 

 dogens is applied to plants which, like palms, appear to grow by addition to the inner 

 parts of the stem. The stem varies in structure in four principal ways : it is either 

 formed by successive additions to the outside of the wood, when it is called exogenous, 

 or by successive additions to its centre, when it is called endogenous, or by the union 

 of the bases of leaves, and the extension of the point of the axis, which is called aero- 

 genous, or by simple elongation or dilatation where no leaves or buds exist, as among 

 Thallogcns. Lindley. 



EXOS1VIOSE and ENDOSMOSE. As some manufacturing processes involve the 

 phenomena expressed by these two words, it appears necessary briefly to explain them. 



When two liquids are separated by a porous sheet of animal membrane, unglazed 

 earthenware, porous stone, or clay, theso liquids gradually diffuse themselves; and 

 supposing salt and water to be on one side of the division, and water only on the 

 other, the saline solution passes in one direction, while the water, though with less 

 intensity, passes in another. 



Instead of the two words introduced by Dutrochot, Professor Graham proposed the 

 use of the single term Osmose (from ufffj.6s, impulsion). 



It was supposed that there was, at the same time, an impulsive force acting from 

 without and another acting from within; that there was indeed a current flowing in, 



