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 historians, he sought to bring to light fresh historical material by patient search for letters, diaries and other manuscripts of value which had escaped the notice of previous students. Indeed, the honour has been claimed for him of being one of the founders of the modern school of historical research.

 DISS, a market town in the southern parliamentary division of Norfolk, England; near the river Waveney (the boundary with Suffolk), 95 m. N.E. by N. from London by the Great Eastern railway. Pop. of urban district (1901) 3745. The town lies pleasantly upon a hill rising above a mere, which drains to the Waveney, having its banks laid out as public gardens. The church of St Mary exhibits Decorated and Perpendicular stone and flint work. There is a corn exchange and the agricultural trade is considerable; brushes and matting are manufactured. The poet and satirist, John Skelton (d. 1529), was rector here in the later part of his life, and is doubtfully considered a native.

 DISSECTION (from Lat. dissecare, to cut apart), the separation into parts by cutting, particularly the cutting of an animal or plant into parts for the purpose of examination or display of its structure.

 DISSENTER (Lat. dis-sentire, to disagree), one who dissents or disagrees in matters of opinion, belief, &c. The term “dissenter” is, however, practically restricted to the special sense of a member of a religious body in England which has, for one reason or another, separated from the Established Church. Strictly, the term includes the English Roman Catholics, who in the original draft of the Relief Act of 1791 were styled “Protesting Catholic Dissenters.” It is in practice, however, restricted to the “Protestant Dissenters” referred to in sec. ii. of the Toleration Act of 1688. The term is not applied to those bodies who dissent from the Established Church of Scotland; and in speaking of members of religious bodies which have seceded from established churches abroad it is usual to employ the term “dissidents” (Lat. dissidere, to dissent). In this connotation the terms “dissenter” and “dissenting,” which had acquired a somewhat contemptuous flavour, have tended since the middle of the 19th century to be replaced by “nonconformist,” a term which did not originally imply secession, but only refusal to conform in certain particulars (e.g. the wearing of the surplice) with the authorized usages of the Established Church. Still more recently the term “nonconformist” has in its turn, as the political attack on the principle of a state establishment of religion developed, tended to give place to the style of “Free Churches” and “Free Churchman.” All three terms are now in use, “nonconformist” being the most usual, as it is the most colourless. (See, &c.)

 DISSOCIATION, a separation or dispersal, the opposite of association. In chemistry the term is given to chemical reactions in which a substance decomposes into two or more substances, and particularly to cases in which associated molecules break down into simpler molecules. Thus the reactions NH4Cl⮂NH3 + HCl, and PCl5⮂PCl3 + Cl2 are instances of the first type; N2O4⮂2NO2, of the second (see ). Electrolytic or ionic dissociation is the separation of a substance in solution into ions (see ; ).

 DISSOLUTION (from Lat. dissolvere, to break up into parts), the act of dissolving or reducing to constituent parts, especially of the bringing to an end an association such as a partnership or building society, and particularly of the termination of an assembly. A dissolution of parliament in England is thus the end of its existence, brought about by the efflux of time in accordance with the Septennial Act 1716, or by an exercise of the royal prerogative. This is done either in person, or by commission, if parliament is sitting; if prorogued, then by proclamation. The word is used as a synonym for end or death.

 DISTAFF, in the early forms of spinning, the “rock” or short stick round one end of which the flax, cotton or wool is loosely wound, and from which it is spun off by the spindle. The word is derived from the Old English distaef, the first part of which is connected with dizen, in modern English seen in “bedizen,” to deck out or embellish, originally “to equip the distaff with flax, &c.,” cf. the German dialectal word Diesse, flax. The last part of the word is “staff.” “Distaff” from early times has been used to symbolize woman’s work (cf. the use of “spinster” for an unmarried woman); thus the “distaff” or “spindle” side of a family refers to the female branch, as opposed to the “spear” or male branch. The 7th of January, the day after Epiphany, was formerly known as St Distaff’s day, as women then began work again after the Christmas holiday.

 DISTILLATION (from the Lat. distillare, more correctly destillare, to drop or trickle down), an operation consisting in the conversion of a substance or mixture of substances into vapours which are afterwards condensed to the liquid form; it has for its object the separation or purification of substances by taking advantage of differences in volatility. The apparatus consists of three parts:—the “retort” or “still,” in which the substance is heated; the “condenser,” in which the vapours are condensed; and the “receiver,” in which the condensed vapours are collected. Generally the components of a mixture will be vaporized in the order of their boiling-points; consequently if the condensates or “fractions” corresponding to definite ranges of temperature be separately collected, it is obvious that a more or less partial separation of the components will be effected. If the substance operated upon be practically pure to start with, or the product of distillation be nearly of constant composition, the operation is termed “purification by distillation” or “rectification”; the latter term is particularly used in the spirit industry. If a complex mixture be operated upon, and a separation effected by collecting the distillates in several portions, the operation is termed “fractional distillation.” Since many substances decompose either at, or below, their boiling-points under ordinary atmospheric pressure, it is necessary to lower the boiling-point by reducing the pressure if it be desired to distil them. This variation is termed “distillation under reduced pressure or in a vacuum.” The vaporization of a substance below its normal boiling-point can also be effected by blowing in steam or some other vapour; this operation is termed “distillation with steam.” “Dry distillation” is the term used when solid substances which do not liquefy on heating are operated upon; “sublimation” is the term used when a solid distils without the intervention of a liquid phase.

Distillation appears to have been practised at very remote times. The Alexandrians prepared oil of turpentine by distilling pine-resin; Zosimus of Panopolis, a voluminous writer of the 5th century, speaks of the distillation of a “divine water” or “panacea” (probably from the complex mixture of calcium polysulphides, thiosulphate, &c., and free sulphur, which is obtained by boiling sulphur with lime and water) and advises “the efficient luting of the apparatus, for otherwise the valuable properties would be lost.” The Arabians greatly improved the earlier apparatus, naming one form the (q.v.); they discovered many ethereal oils by distilling plants and plant juices, alcohol by the distillation of wine, and also distilled water. The alchemists gave great attention to the method, as is shown by the many discoveries made. Nitric, hydrochloric and sulphuric acids, all more or less impure, were better studied; and many ethereal oils were discovered. Prior to about the 18th century three forms of distillation were practised: (1) destillatio per ascensum, in which the retort was heated from the bottom, and the vapours escaped from the top; (2) destillatio per latus, in which the vapours escaped from the side; (3) destillatio per descensum, in which the retort was heated at the top, and the vapours led off by a pipe passing through the bottom. According to K. B. Hoffmann the earliest mention of destillatio per descensum occurs in the writings of Aetius, a Greek physician who flourished at about the end of the 5th century.

In modern times the laboratory practice of distillation was greatly facilitated by the introduction of the condenser named after Justus von Liebig; A. Kolbe and E. Frankland introduced the “reflux condenser,” i.e. a condenser so placed that the condensed vapours return to the distilling flask, a device permitting the continued boiling of a substance with little loss; W.<section end="Distillation" />