DISSONANCE DISTRESS. 



691 



events in Poland have again placed the dissidents on 

 an equal footing with the Catholics. 



DISSONANCE; that eflect which results from 

 the union of two sounds not in accord with each 

 other. The ancients considered thirds and sixths as 

 dissonances; and, in fact, every chord, except the 

 perfect concord, is a dissonant chord. The old theories 

 include an infinity of Dissonances, but the present re- 

 ceived system reduces them to a comparatively small 

 number. One rule, admitted both by the ancients and 

 the moderns, is, that of two notes, dissonant between 

 themselves, the dissonance appertains to that one of 

 the two which is most remote from the concord. 



DISTICH ; a couplet of verses, especially one 

 consisting of an hexameter and pentameter ; as, 



" Turpe quidem dictn : aed, si mndo vera fatemur, 

 Vulgus amicitias utilitate probat." 



The hexameter, which flows on in an uninterrupted 

 course, being adapted to the expression of feeling, 

 and the pentameter, which is broken by two nearly 

 equal divisions, expressing subdued emotion, this dis- 

 position is undoubtedly best suited to the elegy (q.v.), 

 and for this reason was called the elegiac measure. 

 At the same time, no form is more suitable for maxims 

 or sentences than the distich. The Greeks, there- 

 fore, composed their epigrams almost exclusively in 

 this form, and the Germans have followed their ex- 

 ample. Other nations, who do not possess this mea- 

 sure, frequently call every piece of poetry in two 

 lines, a distich. 



DISTILLATION is an art founded upon the dif- 

 ferent tendencies which bodies have to pass into va- 

 pour, and to be condensed again by cold, and is per- 

 formed hi order to separate them from each other, 

 when combined, or when they become products of 

 chemical action. Its use is very important in obtain- 

 ing spirits, essences, volatile oils, &c. The most 

 common method of conducting this process consists 

 in placing the liquid to be distilled in a vessel called 

 a still, made of copper, having a movable head, with 

 a swan-like neck, which is so formed as to fit a coiled 

 tube, packed away in a tub of water constantly kept 

 cold, and which is termed a refrigeratory. The fire 

 is applied either immediately to the still, or medi- 

 ately, by means of a water or sand-bath. The liquid 

 to be obtained rises, in vapour, into the head of the 

 still, and, passing down the curved tube, or worm, 

 becomes condensed, and makes its exit in a liquid 

 state. The still should be constructed with a diame- 

 ter considerably greater than its height, in order to 

 expose a larger surface to the fire ; and the tube 

 should not be so narrow as to impede the passage of 

 the vapour into the worm. 



An improvement made by Mr Tennant in this 

 apparatus, consists in introducing the spiral tube into 

 the body of a second still, so that the heat from the 

 condensation of the steam, passing through the tube, 

 is applied to the distillation of liquor in the second. 

 The pressure of the atmosphere is removed from th? 

 latter, by connecting it with an air-tight receiver, 

 kept cool. .The air in this receiver is allowed to 

 escape at the commencement of the operation ; its 

 place is occupied by the steam from the liquor, 

 which being condensed, a vacuum is kept up, whence 

 the distillation proceeds without any further heat 

 being directly applied to the second still. The form 

 of distilling apparatus is called the double still. 



The process introduced by Mr Barry, for preparing 

 vegetable extracts and inspissated juices, by evapo- 

 ration in vacua, is of a somewhat similar nature- 

 The apparatus consists of a hemispherical still, made 

 of cast iron, and polished within. It is closed by an 

 air-tight, flat cover, through which rises a wide tube, 

 which is then bent downwards, and terminates in a 

 Inge copper globe, of a capacity three or four times 



greater than that of the still. In this tube there is 

 a stop-cock, between the still and the globe. When 

 evaporation is to be performed, the vegetable juice or 

 infusion is poured into the polished iron still, through 

 an opening, which is then closed, made air-tight, and 

 covered with water. In order to produce a vacuum, 

 the connexion between the still and copper receiver is 

 interrupted, by shutting the stop-cock, and steam 

 from a boiler is introduced by a pipe into the latter, 

 till the whole of the air is expelled from it. This 

 takes usually about five minutes, and is known by 

 the steam issuing from the globe uncondensed. 

 The copper sphere is then closed, and the com- 

 munication restored between it and the still, by 

 opening the stop-cock, when the greater part of the 

 air in the latter rushes into the former. The stop- 

 cock is again closed, and the globe again filled with 

 steam as before. By the condensation of this 

 steam a vacuum is again produced, which, on open- 

 ing the stop-cock, extracts the greater portion of 

 the air remaining in the still : in short, by repeating 

 these exliaustions five or six times, an almost per- 

 fect vacuum is obtained, both in the still and receiv- 

 er. Heat is then applied to the water bath, in 

 which the still is placed, until the juice within 

 begins to boil, which is ascertained by inspection 

 through a piece of thick glass, fixed firmly in the 

 upper part of the apparatus. 



As, in a vacuum, fluids boil nearly 124 degrees be- 

 low their usual boiling temperature, water passes into 

 ebullition, in such circumstances, at 9 Fahr., or 

 a little above it ; and it is never found necessary to 

 heat the juice above a temperature of 100. The 

 evaporation is continued till the fluid is inspissated to 

 the proper extent, which is judged of by its ap- 

 pearance through the glass. Extracts prepared in 

 this way are found to be greatly preferable to those 

 obtained by evaporation at a high temperature : they 

 are considerably stronger, as the active principles in 

 the juices are not decomposed by reaction between 

 their elements, favoured by heat ; and they are free 

 from all burnt flavour, or empyreuma. There are 

 many operations, however, in which liquids are em- 

 ployed, that would corrode metallic vessels : in such 

 cases, vessels are employed, constructed either of 

 glass, platinum, or stone ware. They are of various 

 forms, generally consisting of two parts, one called 

 a retort, and the other a receiver. The receiver is 

 sometimes tubulated, with a stopper adapted to the 

 tubulature. In some cases of distillation, the product 

 is not entirely a vapour which may be condensed ; 

 but there is disengaged an elastic fluid, which is 

 incondensable. This gas is allowed to pass off by a 

 tube from the tubulature ; the tube terminating in a 

 vessel of water, and thus enabling us to collect the 

 gas in an inverted jar. In certain cases, the product 

 designed to be obtained by distillation is an elastic 

 fluid, not condensable by itself, but capable of 

 being condensed by being transmitted through 

 water. A contrivance called IVoulfe's apparatus is 

 used for this purpose. A liquid obtained by distillation 

 is sometimes not perfectly pure, or it is dilute, from the 

 intermixture of water, that has been elevated in vapour 

 along with it. By repeating the distillation of it a 

 second or a third time, it is rendered more pure and 

 strong. This latter process is named rectification, or 

 sometimes concentration. See the article fVhiskey, 

 where practical details will be given of the most ap- 

 proved methods of distilling that spirit as practised 

 in Scotland. 



DISTRESS, in law (from the Latin disfringo, to 

 distrain), is the taking of a personal chattel of a 

 wrong-doer, or a tenant, in order to obtain satisfac- 

 tion for the wrong done, or for rent or service due. 

 The thing taken is also called a distress. A distress 

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