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EVAPORATION. 



EVIDENCE. 



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have vapours of such low elasticities, that the highest natural tem- 

 perature cannot convert them into vapour : and hence Mr. Faraday 

 concludes that the atmosphere does not contain any vapours of earthy 

 or metallic substances. Camphor evaporates readily at ordinary tem- 

 peratures, and deposits crystals on that side of the glass vessel which 

 contains it which is nearest to the light. When ice in introduced into 

 the Torricellian vacuum it immediately depresses the mercurial 

 column upwards of j&ths of an inch. This is at 32, but even at zero 

 the tension of the vapour of ice amounts to i^,ths inch : it is in 

 consequence of this evaporation that drifts of snow and patches of 

 ice disappear even during the continuance of severe frost. 



A few cues occur in which a body passing from a liquid to a solid 

 form acquires thereby an increase of temperature, and the most 

 remarkable case is afforded in the freezing of water. While still 

 existing in a liquid state, water has had its temperature reduced so 

 low, that a Fahrenheit's thermometer hi it indicated no more, than 

 5 ; but on being made to crystallise, by agitation or otherwise, so 

 much caloric was immediately evolved, that the thermometer rose to 

 82. But when, by evaporation, a liquid is transformed into a vapour, 

 heat is abstracted, and a thermometer in the liquid indicates a depres- 

 sion of temperature, or the liquid becomes cooled. In some parts of 

 India, ice is produced by exposing water during the night in flat un- 

 glazed earthen vessels resting upon any imperfectly conducting sub- 

 stances, as sugar-canes, dry stems of maize, and the like. The dryness 

 of the air allows a considerable evaporation to take place, and a thin 

 film of ice is produced. Similar processes are employed in other 

 countries for the purpose of reducing the temperature of liquids. 

 [COOLER.] To a similar cause must be referred the icy caverns of the 

 Jura, of Connecticut, and of Illetzkaya in the steppes of the Kirghis ; 

 namely, the powerful evaporation of moisture caused by the vicinity 

 of the warm and dry external air. 



The pressure of the atmosphere on the surface of a liquid may 

 retard but does not prevent the evaporation from taking place. Vapours, 

 like] gases, mix with other aeriform fluids according to their own laws, 

 and as if they were diffused through a vacuum. Each atmosphere of 

 vapour in the compound atmosphere acts on its own particles alone ; 

 so that the aqueous vapour in the atmosphere acts by pressure only 

 on itself. The time that is occupied before a given space is saturated 

 with a vapour' varies inversely with the pressure ; and with different 

 vapours, under the same pressures, the time varies with the diffusive- 

 ness of the vapour. [DIFFUSION.] The conversion of a liquid into a 

 vapour is facilitated by placing the vessel containing the liquid under 

 the receiver of an air-pump and extracting the air : but the vapour 

 itself acts by its elastic force on the surface of the liquid, and impedes, 

 at least for a time, the escape of more than a certain quantity. 

 Daniell found that when water was evaporated under the receiver of 

 an air-pump in the presence of sulphuric acid, the rate of evaporation 

 was inversely as the pressure. Consequently the cooling process may 

 be greatly accelerated by employing some means of absorbing the 

 vapour as fast as it is formed, thus allowing the evaporation to go on 

 without impediment. The means of accomplishing this end were dis- 

 covered by Sir John Leslie, who placed a shallow open vessel contain- 

 ing sulphuric acid or muriate of lime along with the vessel containing 

 the water from which an evaporation was to take place under the 

 receiver of the air-pump ; when the vapour was absorbed as it rose, 

 and the water was speedily converted into ice. [FBEEZIXQ APPARATUS ; 

 CRYOPHORUS.] 



If a glass bottle containing water be covered with a cloth which is 

 kept constantly wet by the application of water, the evaporation from 

 the wet cloth will soon diminish the temperature of the water which 

 is in the bottle. A similar effect is produced, but in a higher degree, 

 on moistening the bottle with some spirit, as alcohol ; and if a cloth 

 dipped in alcohol be applied to the ball of a thermometer, the mercury 

 in the tube will descend while the evaporation continues : the cooling 

 is found to be so much greater as the spirit is more volatile ; and it 

 appears to be the greatest when ether is employed. 



The degree of cold thus produced is increased by any means which 

 will accelerate the evaporation : thus, by wrapping a piece of linen 

 dipped in ether round the ball of a mercurial thermometer, and ex- 

 posing the apparatus to a current of air, the mercury in the tube has 

 been made to fall as much as 45. Dr. Cullen (' Essays, Physical and 

 Literary '), of Edinburgh put a small quantity of water into a thin 

 glass tube which was suspended in a vessel containing ether; and 

 then, on placing the apparatus under the receiver of an air-pump and 

 rapidly exhausting the air, the evaporation of the ether caused such 

 a diminution of heat in the water that it was converted into ice. By 

 a similar process, using sulphuret of carbon instead of ether, Dr. 

 Marcet ('Phil. Trans.,' 1813) succeeded in freezing mercury. Still 

 more remarkable cases are given under EBULLITION. 



For the method of ascertaining the amount of moisture in the air 

 tinder any given temperature, see HYGROMETER. The supposed connec- 

 tion between evaporation and electricity is noticed under ELECTRICITY, 

 ATMOSPHERIC ; and the importance of evaporation as a meteorological 

 agent will be further considered under RAIN; METEOROLOGY, &c.; 

 but we may here refer to the old opinion advocated by the Abbe' 

 Kollet and others, that " electricity increases the natural evaporation 

 of fluids," and that it is more efficient in this respect when the 

 vessels which contain them are conductors. Mr. Rowell (' Cause of 



Rain,' Oxford, 1859) suspended by means of silk threads, in a warm 

 room over an oven in daily use, two shallow vessels each containing 

 8 ozs. of water. From one of the vessels was hung a small copper 

 wire passing from the water to the earth. In the course of twenty-five 

 hours the insulated vessel lost 2 ozs. 11 dwts. 15 grs., and the other 

 vessel Sozs. 6 dwts, thus showing an excess of evaporation from the 

 non-insulated vessel of 1 4 dwts. 9 grs. A similar result was obtained 

 when the vessels were exposed to the sun. 



EVECTION. [LUNAR THEORY.] 



EVERITT'S SALT. [CYANOGEN, diluted >,ydrocyan!<- anil.] 



EVERNESIC ACID. Synonymous with EVERSISIC ACID. 



EVERNIC ACID (C M H,,0 14 ?), a crystalline .acid, homologous 

 with lecanoric acid, extracted from a species of lichen, the J. 

 pruntutri. [LICHENS, COLOURING MATTERS OF.] 



EVERNINIC ACID. [LICHENS, COLOURING MATTERS OP.] 



EVIDENCE (Judicial) denotes, in jurisprudence, the proper means 

 of evincing the true state of facts which have become the object of 

 judicial investigation ; and the just use of such means for that end in 

 these investigations is the proper object of those established rules which 

 are received in the courts of justice as the law of evidence. This law 

 originates in the practice of the tribunals, continues into the latest 

 times for the most part still unwritten, and long retains the character 

 of the age which conceived and formed it for immediate service. 

 Gradually the course of ages, changing the manners and continually 

 adding to the moral and intellectual wealth of the nation, brings with 

 it the necessity at length of departing somewhat from the tradition of 

 the fathers. Reforms are introduced by positive enactment, and other 

 reforms succeed as confidence increases with experience of the improve- 

 ment effected thereby in the administration of justice. In this way 

 our statute-book comes to exhibit at distant intervals the traces of 

 change, which might be studied with advantage, relative to the history 

 and character of the nation, but from which little information could be 

 derived respecting the principles and rules that constitute this branch 

 of English jurisprudence. The great bulk of these remain at this day, 

 as they have been for ages, the subject of tradition, the common law of 

 the courts, the familiar rules of daily practice in the administration of 

 justice. But we are apt to forget this when we turn to Justinian's 

 ' Digest,' and point with something like contempt to one short chapter 

 which appears there, as though it necessarily comprised all that was 

 known to the Roman law on the subject of evidence. This is probably 

 an error of the same kind with his who should assume that in the 

 fragmentary provisions of our statute-book he finds the whole of the 

 English law upon the same subject ; but the wrong would be so much 

 greater, as it is done to the memory of a people whose jurisprudence 

 has been the light of modern nations and the cherished wealth of the 

 greatest minds, and which for its wisdom and rectitude still secures 

 them the position and authority of the masters of the world. 



Judicial evidence, considered with regard to its sources, is deri- 

 vable from living witnesses, and from written instruments ; aud viewed 

 with respect to its production in court, and admissibility as the means 

 of judicial inquiry, it is subject to conditions which in the order of 

 things demand our earliest attention. 



The first great condition of the admissibility of living testimony in 

 this country is that it must be given under the sanction of an oath. 

 It suffices, however, that it be such an oath as is binding on the con- 

 science of the witness. No exclusive ceremony or form of words is 

 prescribed by our law, and no further inquiry into the faith of the 

 witness is permitted than is necessary to ascertain whether he acknow- 

 ledges the existence and moral government of the Divine Being, and 

 that he will punish falsehood and perjury, either in this life or that 

 which is to come. Even that inquiry is not volunteered by the judge, 

 though it is permitted to be made by the adverse party ; for it is a 

 presumption of law that every person, in this country, of sufficient 

 mental capacity, entertains this faith, and the usual form of oath is 

 tendered without preliminary question. But obvious incapacity of 

 mind, whether it be the immaturity of young children or the defect of 

 the insane, rebuts this presumption of the law, aud imposes on the 

 court the duty of making previous inquiry into the state of the 

 witness's knowledge with regard to the nature of an oath. 



The exemption, at an early period, from this necessity, of certain 

 religious sects who entertain conscientious objections to oaths of any 

 description, has recently been extended to all persons who allege con- 

 scientious motives for their refusal or reluctance to take the oath. 

 This is a modification, still in the spirit of the general rule, rather than 

 any exception to it, made in favour of tender consciences which are 

 hindered from following the common practice by a scrupulous and 

 reverent obedience to what they regard as the Divine Will. 



Scarcely more an exception than this is the admission in evidence 

 upon trials for homicide of the dying declaration of the injured person, 

 who in that condition makes a statement unsworn of the circumstances 

 under which he received his injury. These statements, says Lord 

 Chief Baron Eyre, " are declarations made in extremity when the party 

 is at the point of death, and when every hope of this world is gone ; 

 when every motive to falsehood is silenced, and the mind is induced 

 by the most powerful considerations to speak the truth ; a situation so 

 solemn and so awful is considered by the law as creating an obligation 

 equal to that which is imposed by a positive oath in a court of 

 justice." 





