180 EBULLITION 



Two strips of ebonite and sheet zinc, when rivotted together, curve very materially 

 with even a moderate heating. A thin strip of ivory, 20 centimes in length, cemented 

 l>y means of isinglass to a similar one of ebonite, forms a delicate thermometer, seeing 

 that its free end moves through several millimeters for one degree. The curvature in 

 consequence of unequal expansion may be most simply demonstrated by the aid of a 

 mere plate of ebonite, for, owing to its bad conductivity, it curves considerably when 

 heated on one side. See CAOUTCHOUC. 



EBONY. Of this black wood three kinds are imported : 



The Mauritius Ebony, which is the blackest and finest grained. 



The East-Indian Ebony, which is not of so good a colour. 



The African Ebony, which is porous and bad in point of colour. 



The ebony of the Mauritius is yielded by the Diospyros Ebenus. Colonel Lloyd 

 says, that this ebony when first cut is beautifully sound, but it splits, like all other 

 woods, from neglectful exposure to the sun. The workmen who use it immerse it in 

 water, as soon as it is felled, for from six to eighteen months ; it is then taken out, and 

 the two ends are secured from splitting by iron rings and wedges. Colonel Lloyd 

 considers that next to the Mauritius, the ebony of Madagascar is the best, and next 

 that of Ceylon. 



The Mauritius ebony is imported in round sticks like scaffold poles, about fourteen 

 inches in diameter. The East-Indian variety comes to us in logs as large as twenty- 

 eight inches diameter, and also in planks. The Cape-of-Good-Hope ebony arrives in 

 England in billets, and is called billet wood, from about three to six feet long and two 

 to four inches thick. 



The uses of ebony are well known. 



White Ebony comes from the Isle of France, and is nmch like box wood. See 

 GREEN EBONY. 



EBUXililoSCOPJB. See EBULLITION ALCOHOLOMETER. 



EBULLITION (Eng. and Fr. ; Kochen, Ger.) Soiling. When the bottom 

 of an open vessel containing water is exposed to heat, the lowest stratum of fluid 

 immediately expands, becomes therefore specifically lighter, and rises, through the 

 colder and heavier particles. The heat is in this way diffused through the whole 

 liquid mass, not by simple communication of that power from particle to particle as in 

 solids called the conduction of heat but by a translation of the several particles 

 from the bottom to the top, and the top to the bottom, in regular succession. This is 

 denominated the carrying power of fluids, being common to both liquid and gaseous 

 bodies. These internal movements may be rendered very conspicuous and instructive, 

 by mingling a little powdered amber with water, contained in a tall glass cylinder, 

 standing upon a sand-bath. That this molecular translation or locomotion is almost 

 the sole mode in which fluids get heated, may be demonstrated by placing the middle 

 of a pretty long glass tube, nearly filled with water, obliquely over an argand flame. 

 The upper half of the liquid will soon boil, but the portion under the middle will con- 

 tinue cool, so that a lump of ice may remain for a considerable time at the bottom. 

 When the heat is rabidly applied, the liquid is thrown into agitation, in consequence of 

 elastic vapour being suddenly generated at the bottom of the vessel, and being as 

 suddenly condensed at a little distance above it by the surrounding cold column. 

 These alternate expansions and contractions of volume become more manifest as the 

 liquid becomes hotter, and constitute the simmering, vibratory sound which is the 

 prelude of ebullition. The whole mass being now heated to a pitch compatible with 

 its permanent elasticity, becomes turbulent and explosive under the continued in- 

 fluence of fire, and emitting more or less copious volumes of vapour, is said to boil. 

 The further elevation of temperature, by the influence of heat, becomes impossible 

 in these circumstances with almost all liquids, because the vapour carries off from 

 them as much heat in a latent state as they are capable of receiving from the fire. 



The temperature at which liquids boil in the open air varies with the degree of 

 atmospheric pressure, being higher as that is increased, and lower as it is diminished. 

 Hence boiling-water is colder by some degrees in an elevated situation, -\\ith a de- 

 pressed barometer, than at the bottom of a coal-pit in fine weather, or, when the 

 barometer is elevated. A high column of liquid also, by resisting the disi-luir^c nf 

 the steam, raises the boiling point. As we ascend from the sea-level, the boiling point 

 becomes lower ; the table at the head of page 181 illustrates this. 



In vacuo all liquids boil at a temperature about 124 F. lower than under the 

 average atmospheric pressure. For a table of elasticities, see VAPOUR. Gay-Lussac 

 has shown that liquids are converted into vapours more readily, or with less turbu- 

 lence, when they are in contact with angular or irregular, than with smooth surfaces ; 

 that they therefore boil at a heat 2 F. lower in nn-taUk- than in glass vessels, pro- 

 bably owing to the greater polish of the latter. For example, if into water about to 

 boil in a glass matrass, iron filings, ground glass, pr any other insoluble powder, be 



