The poets completely ruled the literature of Denmark during this period. There were, however, eminent men in other departments of letters, and especially in philology. Rasmus Christian Rask (1787-1832) was one of the most original and gifted linguists of his age. His grammars of Old Frisian, Icelandic and Anglo-Saxon were unapproached in his own time, and are still admirable. Niels Matthias Petersen (1791-1862), a disciple of Rask, was the author of an admirable History of Denmark in the Heathen Antiquity, and the translator of many of the sagas. Martin Frederik Arendt (1773-1823), the botanist and archaeologist, did much for the study of old Scandinavian records. Christian Molbech (1783-1857) was a laborious lexicographer, author of the first good Danish dictionary, published in 1833. In Joachim Frederik Schouw (1789-1852), Denmark produced a very eminent botanist, author of an exhaustive Geography of Plants. In later years he threw himself with zeal into politics. His botanical researches were carried on by Frederik Liebmann (1813-1856). The most famous zoologist contemporary with these men was Salomon Dreier (1813-1842).

The romanticists found their philosopher in a most remarkable man, Sren Aaby Kierkegaard (1813-1855), one of the most subtle thinkers of Scandinavia, and the author of some brilliant philosophical and polemical works. A learned philosophical writer, not to be compared, however, for genius or originality to Kierkegaard, was Frederik Christian Sibbern (1785-1872). He wrote a dissertation On Poetry and Art (3 vols., 1853-1869) and The Contents of a MS. from the Year 2135 (3 vols., 1858-1872).

Among novelists who were not also poets was Andreas Nikolai de Saint-Aubain (1798-1865), who, under the pseudonym of Carl Bernhard, wrote a series of charming romances. Mention must also be made of two dramatists, Peter Thun Feorsom (1777-1817), who produced an excellent translation of Shakespeare (1807-1816), and Thomas Overskou (1798-1873), author of a long series of successful comedies, and of a history of the Danish theatre (5 vols., Copenhagen, 1854-1864).

Other writers whose names connect the age of romanticism with a later period were Meyer Aron Goldschmidt (1819-1887), author of novels and tales; Herman Frederik Ewald (1821-1908), who wrote a long series of historical novels; Jens Christian Hostrup (1818-1892), a writer of exquisite comedies; and the miscellaneous writer Erik Bgh (1822-1899). In zoology, J. J. S. Steenstrup (1813-1898); in philology, J. N. Madvig (1804-1886) and his disciple V. Thomsen (b. 1842); in antiquarianism, C. J. Thomsen (1788-1865) and J. J. Asmussen Worsaae (1821-1885); and in philosophy, Rasmus Nielsen (1809-1884) and Hans Brchner (1820-1875), deserve mention.

The development of imaginative literature in Denmark became very closely defined during the latter half of the 19th century. The romantic movement culminated in several poets of great eminence, whose deaths prepared the way for a new school. In 1874 Bdtcher passed away, in 1875 Hans Christian Andersen, in the last week of 1876 Winther, and the greatest of all, Frederik Paludan-Mller. The field was therefore left open to the successors of those idealists, and in 1877 the reaction began to be felt. The eminent critic, Dr Georg Brandes (q.v.), had long foreseen the decline of pure romanticism, and had advocated a more objective and more exact treatment of literary phenomena. Accordingly, as soon as all the great planets had disappeared, a new constellation was perceived to have risen, and all the stars in it had been lighted by the enthusiasm of Brandes. The new writers were what he called Naturalists, and their sympathies were with the latest forms of exotic, but particularly of French literature. Among these fresh forces three immediately took place as leaders—Jacobsen, Drachmann and Schandorph. In J. P. Jacobsen (q.v.; 1847-1885) Denmark was now taught to welcome the greatest artist in prose which she has ever possessed; his romance of Marie Grubbe led off the new school with a production of unexampled beauty. But Jacobsen died young, and the work was really carried out by his two companions. Holger Drachmann (q.v.; 1846-1908) began life as a marine painter; and a first little volume of poems, which he published in 1872, attracted slight attention. In 1877 he came forward again with one volume of verse, another of fiction, a third of travel; in each he displayed great vigour and freshness of touch, and he rose at one leap to the highest position among men of promise. Drachmann retained his place, without rival, as the leading imaginative writer in Denmark. For many years he made the aspects of life at sea his particular theme, and he contrived to rouse the patriotic enthusiasm of the Danish public as it had never been roused before. His various and unceasing productiveness, his freshness and vigour, and the inexhaustible richness of his lyric versatility, early brought Drachmann to the front and kept him there. Meanwhile prose imaginative literature was ably supported by Sophus Schandorph (1836-1901), who had been entirely out of sympathy with the idealists, and had taken no step while that school was in the ascendant. In 1876, in his fortieth year, he was encouraged by the change in taste to publish a volume of realistic stories, Country Life, and in 1878 a novel, Without a Centre. He has some relation with Guy de Maupassant as a close analyst of modern types of character, but he has more humour. He has been compared with such Dutch painters of low life as Teniers. His talent reached its height in the novel called Little Folk (1880), a most admirable study of lower middle-class life in Copenhagen. He was for a while, without doubt, the leading living novelist, and he went on producing works of great force, in which, however, a certain monotony is apparent. The three leaders had meanwhile been joined by certain younger men who took a prominent position. Among these Karl Gjellerup and Erik Skram were the earliest. Gjellerup (b. 1857), whose first works of importance date from 1878, was long uncertain as to the direction of his powers; he was poet, novelist, moralist and biologist in one; at length he settled down into line with the new realistic school, and produced in 1882 a satirical novel of manners which had a great success, The Disciple of the Teutons. Erik Skram (b. 1847) had in 1879 written a solitary novel, Gertrude Coldbjrnsen, which created a sensation, and was hailed by Brandes as exactly representing the "naturalism" which he desired to see encouraged; but Skram has written little else of importance. Other writers of reputation in the naturalistic school were Edvard Brandes (b. 1847), and Herman Bang (b. 1858). Peter Nansen (b. 1861) has come into wide notoriety as the author, in particularly beautiful Danish, of a series of stories of a pronouncedly sexual type, among which Maria (1894) has been the most successful. Meanwhile, several of the elder generation, unaffected by the movement of realism, continued to please the public. Three lyrical poets, H. V. Kaalund (1818-1885), Carl Ploug (1813-1894) and Christian Richardt (1831-1892), of very great talent, were not yet silent, and among the veteran novelists were still active H. F. Ewald and Thomas Lange (1829-1887). Ewald's son Carl (1856-1908) achieved a great name as a novelist, but did his most characteristic work in a series of books for children, in which he used the fairy tale, in the manner of Hans Andersen, as a vehicle for satire and a theory of morals. During the whole of this period the most popular writer of Denmark was J. C. C. Brosbll (1816-1900), who wrote, under the pseudonym Carit Etlar, a vast number of tales. Another popular novelist was Vilhelm Bergse (b. 1835), author of In the Sabine Mountains (1871), and other romances. Sophus Bauditz (b. 1850) persevered in composing novels which attain a wide general popularity. Mention must be made also of the dramatist Christian Molbech (1821-1888).

Between 1885 and 1892 there was a transitional period in Danish literature. Up to that time all the leaders had been united in accepting the naturalistic formula, which was combined with an individualist and a radical tendency. In 1885, however, Drachmann, already the recognized first poet of the country, threw off his allegiance to Brandes, denounced the exotic tradition, declared himself a Conservative, and took up a national and patriotic attitude. He was joined a little later by Gjellerup, while Schandorph remained stanchly by the side of Brandes. The camp was thus divided. New writers began to make their appearance, and, while some of these were stanch to Brandes, others were inclined to hold rather with Drachmann. Of the authors who came forward during this period of transition, the strongest novelist proved to be Hendrik Pontoppidan (b. 1857). In some of his books he reminds the reader of Turgeniev. Pontoppidan published in 1898 the first volume of a great novel entitled Lykke-Per, the biography of a typical Jutlander named Per Sidenius, a work to be completed in eight volumes. From 1893 to 1909 no great features of a fresh kind revealed themselves. The Danish public, grown tired of realism, and satiated with pathological phenomena, returned to a fresh study of their own national characteristics. The cultivation of verse, which was greatly discouraged in the eighties, returned. Drachmann was supported by excellent younger poets of his school. J. J. Jrgensen (b. 1866), a Catholic decadent, was very prolific. Otto C. Fnss (b. 1853) published seven little volumes of graceful lyrical poems in praise of gardens and of farm-life. Andreas Dolleris (b. 1850), of Vejle, showed himself an occasional poet of merit. Alfred Ipsen (b. 1852) must also be mentioned as a poet and critic. Valdemar Rrdam, whose The Danish Tongue was the lyrical success of 1901, may also be named. Some attempts were made to transplant the theories of the symbolists to Denmark, but without signal success. On the other hand, something of a revival of naturalism is to be observed in the powerful studies of low life admirably written by Karl Larsen (b. 1860).

The drama has long flourished in Denmark. The principal theatres are liberally open to fresh dramatic talent of every kind, and the great fondness of the Danes for this form of entertainment gives unusual scope for experiments in halls or private theatres; nothing is too eccentric to hope to obtain somewhere a fair hearing. Drachmann produced with very great success several romantic dramas founded on the national legends. Most of the novelists and poets already mentioned also essayed the stage, and to those names should be added these of Einar Christiansen (b. 1861), Ernst von der Recke (b. 1848), Oskar Benzon (b. 1856) and Gustav Wied (b. 1858).

In theology no names were as eminent as in the preceding generation, in which such writers as H. N. Clausen (1793-1877), and still more Hans Lassen Martensen (1808-1884), lifted the prestige of Danish divinity to a high point. But in history the Danes have been very active. Karl Ferdinand Allen (1811-1871) began a comprehensive history of the Scandinavian kingdoms (5 vols., 1864-1872). Jens Peter Trap (1810-1885) concluded his great statistical account of Denmark in 1879. The 16th century was made the subject of the investigations of Troels Lund (q.v.). About 1880 several of the younger historians formed the plan of combining to investigate and publish the sources of Danish history; in this the indefatigable Johannes Steenstrup (b. 1844) was prominent. The domestic history of the country began, about 1885, to occupy the attention of Edvard Holm (b. 1833), O. Nielsen and the veteran P. Frederik Barfod (1811-1896). The naval histories of G. Ltken attracted much notice. Besides the names already mentioned, A. D. Jrgensen (1840-1897), J. Fredericia (b. 1849), Christian Erslev (b. 1852) and Vilhelm Mollerup have all distinguished themselves in the excellent school of Danish historians. In 1896 an elaborate composite history of Denmark was undertaken by some leading historians (pub. 1897-1905). In philosophy nothing has recently been published of the highest value. Martensen's Jakob Bhme (1881) belongs to an earlier period. H. Hffding (b. 1843) has been the most prominent contributor to psychology. His Problems of Philosophy and his Philosophy of Religion were translated into English in 1906. Alfred Lehmann (b. 1858) has, since 1896, attracted a great deal of attention by his sceptical investigation of psychical phenomena. F. Rnning has written on the history of thought in Denmark. In the criticism of art, Julius Lange (1838-1896), and later Karl Madsen, have done excellent service. In literary criticism Dr Georg Brandes is notable for the long period during which he remained predominant. His was a steady and stimulating presence, ever pointing to the best in art and thought, and his influence on his age was greater than that of any other Dane.

AUTHORITIES.—R. Nyerup, Den danske Digtekunsts Historie (1800-1808), and Almindeligt Literaturlexikon (1818-1820); N. M. Petersen, Literaturhistorie (2nd ed., 1867-1871, 5 vols.); Overskou, Den danske Skueplads (1854-1866, 5 vols.), with a continuation (2 vols., 1873-1876) by E Collin; Chr. Bruun, Bibliotheca Danica (3 vols., 1872-1896); Bricka, Dansk biografisk Lexikon (1887-1901); J. Paludan, Danmarks Literatur i Middelalderen (Copenhagen, 1896); P. Hansen, Illustreret Dansk Literaturhistorie (3 vols., 1901-1902); F. W. Horn, History of the Scandinavian North from the most ancient times to the present (English translation by Rasmus B. Anderson (Chicago, 1884), with bibliographical appendix by Thorwald Solberg); Ph. Schweitzer, Geschichte der Skandinavischen Litteratur (3 pts., Leipzig, 1886-1889), forming vol. viii. of the Geschichte der Weltlitteratur. See also Brandes, Kritiker og Portraiter (1870); Brandes, Danske Ditgere (1877); Marie Herzfeld, Die Skandinavische Litteratur und ihre Tendenzen (Berlin and Leipzig, 1898); Hjalmar Hjorth Boyesen, Essays on Scandinavian Literature (London, 1895); Edmund Gosse, Studies in the Literature of Northern Europe (new ed., London, 1883); Vilhelm Andersen, Litteraturbilleder (Copenhagen, 1903); A. P. J. Schener, Kortfattet Indledning til Romantikkus Periode i Danmarks Litteratur (Copenhagen, 1894). (E. G.)

FOOTNOTES:

[1] It is true the university was established on the 9th of September 1537, but its influence was of very gradual growth and small at first.

[2] Collected as Samling af gamle danske Love (5 vols., Copenhagen, 1821-1827).

[3] Henrik Harpestraengs Laegebog (ed. C. Molbech, Copenhagen, 1826).

[4] Ed. C. Molbech (Copenhagen, 1825).

[5] See Povel Eliesens danske Skrifter (Copenhagen, 1855, &c.), edited by C. E. Secher.

[6] See Monumenta historiae Danicae (ed. H. Rrdam, vol. i., 1873).

[7] Ed. Sophus Birket Smith (Copenhagen, 1868), who also edited the comedies ascribed to Chr. Hansen as De tre aeldste danske Skuespil (1874), and the works of Ranch (1876).

[8] His works were edited by Gustav Storm (Christiania, 1877-1879).

[9] See Fr. W. Horn, Peder Syv (Copenhagen, 1878).

[10] See A. C. L. Heiberg, Thomas Kingo (Odense, 1852).

[11] His collected works were edited by Fr. Barford (Copenhagen, 5th ed., 1879).

[12] Wessel's Digte (3rd ed., 1895) are edited by J. Levin, with a biographical introduction.

[13] A biography by his friend, K. L. Rahbek, is prefixed to a selection of his poetry (6 vols., 1824-1829).

[14] See F. L. Liebenberg, Schack Staffeldts samlede Digte (2 vols., Copenhagen, 1843), and Samlinger til Schack Staffeldts Levnet (4 vols., 1846-1851).

[15] Blicher's Tales were edited by P. Hansen (3 vols., Copenhagen, 1871), and his Poems in 1870.

[16] Edited (3 vols., 2nd ed., 1855, Copenhagen) by F. L. Liebenberg.



DENNERY, or D'ENNERY, ADOLPHE (1811-1899), French dramatist and novelist, whose real surname was PHILIPPE, was born in Paris on the 17th of June 1811. He obtained his first success in collaboration with Charles Desnoyer in mile, ou le fils d'un pair de France (1831), a drama which was the first of a series of some two hundred pieces written alone or in collaboration with other dramatists. Among the best of them may be mentioned Gaspard Hauser (1838) with Anicet Bourgeois; Les Bohmiens de Paris (1842) with Eugne Grang; with Mallian, Marie-Jeanne, ou la femme du peuple (1845), in which Madame Dorval obtained a great success; La Case d'Oncle Tom (1853); Les Deux Orphelines (1875), perhaps his best piece, with Eugne Cormon. He wrote the libretto for Gounod's Tribut de Zamora (1881); with Louis Gallet and douard Blan he composed the book of Massenet's Cid (1885); and, again in collaboration with Eugne Cormon, the books of Auber's operas, Le Premier Jour de bonheur (1868) and Rve d'amour (1869). He prepared for the stage Balzac's posthumous comedy Mercadet ou le faiseur, presented at the Gymnase theatre in 1851. Reversing the usual order of procedure, Dennery adapted some of his plays to the form of novels. He died in Paris in 1899.



DENNEWITZ, a village of Germany, in the Prussian province of Brandenburg, near Jterbog, 40 m. S.W. from Berlin. It is memorable as the scene of a decisive battle on the 6th of September 1813, in which Marshal Ney, with an army of 58,000 French, Saxons and Poles, was defeated with great loss by 50,000 Prussians under Generals Blow (afterwards Count Blow of Dennewitz) and Tauentzien. The site of the battle is marked by an iron obelisk.



DENNIS, JOHN (1657-1734), English critic and dramatist, the son of a saddler, was born in London in 1657. He was educated at Harrow School and Caius College, Cambridge, where he took his B.A. degree in 1679. In the next year he was fined and dismissed from his college for having wounded a fellow-student with a sword. He was, however, received at Trinity Hall, where he took his M.A. degree in 1683. After travelling in France and Italy, he settled in London, where he became acquainted with Dryden, Wycherley and others; and being made temporarily independent by inheriting a small fortune, he devoted himself to literature. The duke of Marlborough procured him a place as one of the queen's waiters in the customs with a salary of 120 a year. This he afterwards disposed of for a small sum, retaining, at the suggestion of Lord Halifax, a yearly charge upon it for a long term of years. Neither the poems nor the plays of Dennis are of any account, although one of his tragedies, a violent attack on the French in harmony with popular prejudice, entitled Liberty Asserted, was produced with great success at Lincoln's Inn Fields in 1704. His sense of his own importance approached mania, and he is said to have desired the duke of Marlborough to have a special clause inserted in the treaty of Utrecht to secure him from French vengeance. Marlborough pointed out that although he had been a still greater enemy of the French nation, he had no fear for his own security. This tale and others of a similar nature may well be exaggerations prompted by his enemies, but the infirmities of character and temper indicated in them were real. Dennis is best remembered as a critic, and Isaac D'Israeli, who took a by no means favourable view of Dennis, said that some of his criticisms attain classical rank. The earlier ones, which have nothing of the rancour that afterwards gained him the nickname of "Furius," are the best. They are Remarks ... (1696), on Blackmore's epic of Prince Arthur; Letters upon Several Occasions written by and between Mr Dryden, Mr Wycherley, Mr Moyle, Mr Congreve and Mr Dennis, published by Mr Dennis (1696): two pamphlets in reply to Jeremy Collier's Short View; The Advancement and Reformation of Modern Poetry (1701), perhaps his most important work; The Grounds of Criticism in Poetry (1704), in which he argued that the ancients owed their superiority over the moderns in poetry to their religious attitude; an Essay upon Publick Spirit ... (1711), in which he inveighs against luxury, and servile imitation of foreign fashions and customs; and Essay on the Genius and Writings of Shakespeare in three Letters (1712).

Dennis had been offended by a humorous quotation made from his works by Addison, and published in 1713 Remarks upon Cato. Much of this criticism was acute and sensible, and it is quoted at considerable length by Johnson in his Life of Addison, but there is no doubt that Dennis was actuated by personal jealousy of Addison's success. Pope replied in The Narrative of Dr Robert Norris, concerning the strange and deplorable frenzy of John Dennis ... (1713). This pamphlet was full of personal abuse, exposing Dennis's foibles, but offering no defence of Cato. Addison repudiated any connivance in this attack, and indirectly notified Dennis that when he did answer his objections, it would be without personalities. Pope had already assailed Dennis in 1711 in the Essay on Criticism, as Appius. Dennis retorted by Reflections, Critical and Satirical ..., a scurrilous production in which he taunted Pope with his deformity, saying among other things that he was "as stupid and as venomous as a hunch-backed toad." He also wrote in 1717 Remarks upon Mr Pope's Translation of Homer ... and A True Character of Mr Pope. He accordingly figures in the Dunciad, and in a scathing note in the edition of 1729 (bk. i. 1. 106) Pope quotes his more outrageous attacks, and adds an insulting epigram attributed to Richard Savage, but now generally ascribed to Pope. More pamphlets followed, but Dennis's day was over. He outlived his annuity from the customs, and his last years were spent in great poverty. Bishop Atterbury sent him money, and he received a small sum annually from Sir Robert Walpole. A benefit performance was organized at the Haymarket (December 18, 1733) on his behalf. Pope wrote for the occasion an ill-natured prologue which Cibber recited. Dennis died within three weeks of this performance, on the 6th of January 1734.

His other works include several plays, for one of which, Appius and Virginia (1709), he invented a new kind of thunder. He wrote a curious Essay on the Operas after the Italian Manner (1706), maintaining that opera was the outgrowth of effeminate manners, and should, as such, be suppressed. His Works were published in 1702, Select Works ... (2 vols.) in 1718, and Miscellaneous Tracts, the first volume only of which appeared, in 1727. For accounts of Dennis see Cibber's Lives of the Poets, vol. iv.; Isaac D'Israeli's essays on Pope and Addison in the Quarrels of Authors, and "On the Influence of a Bad Temper in Criticism" in Calamities of Authors; and numerous references in Pope's Works.



DENOMINATION (Lat. denominare, to give a specific name to), the giving of a specific name to anything, hence the name or designation of a person or thing, and more particularly of a class of persons or things; thus, in arithmetic, it is applied to a unit in a system of weights and measures, currency or numbers. The most general use of "denomination" is for a body of persons holding specific opinions and having a common name, especially with reference to the religious opinions of such a body. More particularly the word is used of the various "sects" into which members of a common religious faith may be divided. The term "denominationalism" is thus given to the principle of emphasizing the distinctions, rather than the common ground, in the faith held by different bodies professing one sort of religious belief. This use is particularly applied to that system of religious education which lays stress on the principle that children belonging to a particular religious sect should be publicly taught in the tenets of their belief by members belonging to it and under the general control of the ministers of the denomination.



DENON, DOMINIQUE VIVANT, BARON DE (1747-1825), French artist and archaeologist, was born at Chalon-sur-Sane on the 4th of January 1747. He was sent to Paris to study law, but he showed a decided preference for art and literature, and soon gave up his profession. In his twenty-third year he produced a comedy, Le Bon Pre, which obtained a succs d'estime, as he had already won a position in society by his agreeable manners and exceptional conversational powers. He became a favourite of Louis XV., who entrusted him with the collection and arrangement of a cabinet of medals and antique gems for Madame de Pompadour, and subsequently appointed him attach to the French embassy at St Petersburg. On the accession of Louis XVI. Denon was transferred to Sweden; but he returned, after a brief interval, to Paris with the ambassador M. de Vergennes, who had been appointed foreign minister. In 1775 Denon was sent on a special mission to Switzerland, and took the opportunity of visiting Voltaire at Ferney. He made a portrait of the philosopher, which was engraved and published on his return to Paris. His next diplomatic appointment was to Naples, where he spent seven years, first as secretary to the embassy and afterwards as charg d'affaires. He devoted this period to a careful study of the monuments of ancient art, collecting many specimens and making drawings of others. He also perfected himself in etching and mezzotinto engraving. The death of his patron, M. de Vergennes, in 1787, led to his recall, and the rest of his life was given mainly to artistic pursuits. On his return to Paris he was admitted a member of the Academy of Painting. After a brief interval he returned to Italy, living chiefly at Venice. He also visited Florence and Bologna, and afterwards went to Switzerland. While there he heard that his property had been confiscated, and his name placed on the list of the proscribed, and with characteristic courage he resolved at once to return to Paris. His situation was critical, but he was spared, thanks to the friendship of the painter David, who obtained for him a commission to furnish designs for republican costumes. When the Revolution was over, Denon was one of the band of eminent men who frequented the house of Madame de Beauharnais. Here he met Bonaparte, to whose fortunes he wisely attached himself. At Bonaparte's invitation he joined the expedition to Egypt, and thus found the opportunity of gathering the materials for his most important literary and artistic work. He accompanied General Desaix to Upper Egypt, and made numerous sketches of the monuments of ancient art, sometimes under the very fire of the enemy. The results were published in his Voyage dans la basse et la haute gypte (2 vols, fol., with 141 plates, Paris, 1802), a work which crowned his reputation both as an archaeologist and as an artist. In 1804 he was appointed by Napoleon to the important office of director-general of museums, which he filled until the restoration in 1815, when he had to retire. He was a devoted friend of Napoleon, whom he accompanied in his expeditions to Austria, Spain and Poland, taking sketches with his wonted fearlessness on the various battlefields, and advising the conqueror in his choice of spoils of art from the various cities pillaged. After his retirement he began an illustrated history of ancient and modern art, in which he had the co-operation of several skilful engravers. He died at Paris on the 27th of April 1825, leaving the work unfinished. It was published posthumously, with an explanatory text by Amaury Duval, under the title Monuments des arts du dessin chez les peuples tant anciens que modernes, recueillis par Vivant Denon (4 vols, fol., Paris, 1829). Denon was the author of a novel, Point de lendemain (1777), of which further editions were printed in 1812, 1876 and 1879.

See J. Renouvier, Histoire de l'art pendant la Rvolution; A. de la Fizelire, L'OEuvre originale de Vivant-Denon (2 vols., Paris, 1872-1873); Roger Portallis, Les Dessinateurs d'illustrations au XVIII^e sicle; D. H. Beraldi, Les Graveurs d'illustrations au XVIII^e sicle.



DENOTATION (from Lat. denotare, to mark out, specify), in logic, a technical term used strictly as the correlative of Connotation, to describe one of the two functions of a concrete term. The concrete term "connotes" attributes and "denotes" all the individuals which, as possessing these attributes, constitute the genus or species described by the term. Thus "cricketer" denotes the individuals who play cricket, and connotes the qualities or characteristics by which these individuals are marked. In this sense, in which it was first used by J. S. Mill, Denotation is equivalent to Extension, and Connotation to Intension. It is clear that when the given term is qualified by a limiting adjective the Denotation or Extension diminishes, while the Connotation or Intension increases; e.g. a generic term like "flower" has a larger Extension, and a smaller Intension than "rose": "rose" than "moss-rose." In more general language Denotation is used loosely for that which is meant or indicated by a word, phrase, sentence or even an action. Thus a proper name or even an abstract term is said to have Denotation. (See CONNOTATION.)



DENS, PETER (1690-1775), Belgian Roman Catholic theologian, was born at Boom near Antwerp. Most of his life was spent in the archiepiscopal college of Malines, where he was for twelve years reader in theology and for forty president. His great work was the Theologia moralis et dogmatica, a compendium in catechetical form of Roman Catholic doctrine and ethics which has been much used as a students' text-book. Dens died on the 15th of February 1775.



DENSITY (Lat. _densus_, thick), in physics, the mass or quantity of matter contained in unit volume of any substance: this is the _absolute density_; the term _relative density_ or _specific gravity_ denotes the ratio of the mass of a certain volume of a substance to the mass of the same volume of some standard substance. Since the weights used in conjunction with a balance are really standard masses, the word "weight" may be substituted for the word "mass" in the preceding definitions; and we may symbolically express the relations thus:—If M be the weight of substance occupying a volume V, then the absolute density [Delta] = M/V; and if m, m_1 be the weights of the substance and of the standard substance which occupy the same volume, the relative density or specific gravity S = m/m_1; or more generally if m_1 be the weight of a volume v of the substance, and m_1 the weight of a volume v_1 of the standard, then S = mv_{1}/m_{1}v. In the numerical expression of absolute densities it is necessary to specify the units of mass and volume employed; while in the case of relative densities, it is only necessary to specify the standard substance, since the result is a mere number. Absolute densities are generally stated in the C.G.S. system, i.e. as grammes per cubic centimetre. In commerce, however, other expressions are met with, as, for example, "pounds per cubic foot" (used for woods, metals, &c.), "pounds per gallon," &c. The standard substances employed to determine relative densities are: water for liquids and solids, and hydrogen or atmospheric air for gases; oxygen (as 16) is sometimes used in this last case. Other standards of reference may be used in special connexions; for example, the Earth is the usual unit for expressing the relative density of the other members of the solar system. Reference should be made to the article GRAVITATION for an account of the methods employed to determine the "mean density of the earth."

In expressing the absolute or relative density of any substance, it is necessary to specify the conditions for which the relation holds: in the case of gases, the temperature and pressure of the experimental gas (and of the standard, in the case of relative density); and in the case of solids and liquids, the temperature. The reason for this is readily seen; if a mass M of any gas occupies a volume V at a temperature T (on the absolute scale) and a pressure P, then its absolute density under these conditions is [Delta] = M/V; if now the temperature and pressure be changed to T_1 and P_1, the volume V_1 under these conditions is VPT/P_{1}T_1, and the absolute density is MP_{1}T/VPT_1. It is customary to reduce gases to the so-called "normal temperature and pressure," abbreviated to N.T.P., which is 0C. and 760 mm.

The relative densities of gases are usually expressed in terms of the standard gas under the same conditions. The density gives very important information as to the molecular weight, since by the law of Avogadro it is seen that the relative density is the ratio of the molecular weights of the experimental and standard gases. In the case of liquids and solids, comparison with water at 4C, the temperature of the maximum density of water; at 0C, the zero of the Centigrade scale and the freezing-point of water; at 15 and 18, ordinary room-temperatures; and at 25, the temperature at which a thermostat may be conveniently maintained, are common in laboratory practice. The temperature of the experimental substance may or may not be the temperature of the standard. In such cases a bracketed fraction is appended to the specific gravity, of which the numerator and denominator are respectively the temperatures of the substance and of the standard; thus 1.093 (0/4) means that the ratio of the weight of a definite volume of a substance at 0 to the weight of the same volume of water 4 is 1.093. It may be noted that if comparison be made with water at 4, the relative density is the same as the absolute density, since the unit of mass in the C.G.S. system is the weight of a cubic centimetre of water at this temperature. In British units, especially in connexion with the statement of relative densities of alcoholic liquors for Inland Revenue purposes, comparison is made with water at 62F. (16.6C); a reason for this is that the gallon of water is defined by statute as weighing 10 lb. at 62F., and hence the densities so expressed admit of the ready conversion of volumes to weights. Thus if d be the relative density, then 10d represents the weight of a gallon in lb.. The brewer has gone a step further in simplifying his expressions by multiplying the density by 1000, and speaking of the difference between the density so expressed and 1000 as "degrees of gravity" (see BEER).

PRACTICAL DETERMINATION OF DENSITIES

The methods for determining densities may be divided into two groups according as hydrostatic principles are employed or not. In the group where the principles of hydrostatics are not employed the method consists in determining the weight and volume of a certain quantity of the substance, or the weights of equal volumes of the substance and of the standard. In the case of solids we may determine the volume in some cases by direct measurement—this gives at the best a very rough and ready value; a better method is to immerse the body in a fluid (in which it must sink and be insoluble) contained in a graduated glass, and to deduce its volume from the height to which the liquid rises. The weight may be directly determined by the balance. The ratio "weight to volume" is the absolute density. The separate determination of the volume and mass of such substances as gunpowder, cotton-wool, soluble substances, &c., supplies the only means of determining their densities. The stereometer of Say, which was greatly improved by Regnault and further modified by Kopp, permits an accurate determination of the volume of a given mass of any such substance. In its simplest form the instrument consists of a glass tube PC (fig. 1), of uniform bore, terminating in a cup PE, the mouth of which can be rendered air-tight by the plate of glass E. The substance whose volume is to be determined is placed in the cup PE, and the tube PC is immersed in the vessel of mercury D, until the mercury reaches the mark P. The plate E is then placed on the cup, and the tube PC raised until the surface of the mercury in the tube stands at M, that in the vessel D being at C, and the height MC is measured. Let k denote this height, and let PM be denoted by l. Let u represent the volume of air in the cup before the body was inserted, v the volume of the body, a the area of the horizontal section of the tube PC, and h the height of the mercurial barometer. Then, by Boyle's law (u - v + al)(h - k) = (u - v)h, and therefore v = u - al(h - k)/k.



The volume u may be determined by repeating the experiment when only air is in the cup. In this case v = 0, and the equation becomes (u + al)(h - k) = uh, whence u = al(h - k)/k. Substituting this value in the expression for v, the volume of the body inserted in the cup becomes known. The chief errors to which the stereometer is liable are (1) variation of temperature and atmospheric pressure during the experiment, and (2) the presence of moisture which disturbs Boyle's law.

The method of weighing equal volumes is particularly applicable to the determination of the relative densities of liquids. It consists in weighing a glass vessel (1) empty, (2) filled with the liquid, (3) filled with the standard substance. Calling the weight of the empty vessel w, when filled with the liquid W, and when filled with the standard substance W_1, it is obvious that W - w, and W_1 - w, are the weights of equal volumes of the liquid and standard, and hence the relative density is (W - w)/(W_1 - w).



Many forms of vessels have been devised. The commoner type of "specific gravity bottle" consists of a thin glass bottle (fig. 2) of a capacity varying from 10 to 100 cc., fitted with an accurately ground stopper, which is vertically perforated by a fine hole. The bottle is carefully cleansed by washing with soda, hydrochloric acid and distilled water, and then dried by heating in an air bath or by blowing in warm air. It is allowed to cool and then weighed. The bottle is then filled with distilled water, and brought to a definite temperature by immersion in a thermostat, and the stopper inserted. It is removed from the thermostat, and carefully wiped. After cooling it is weighed. The bottle is again cleaned and dried, and the operations repeated with the liquid under examination instead of water. Numerous modifications of this bottle are in use. For volatile liquids, a flask provided with a long neck which carries a graduation and is fitted with a well-ground stopper is recommended. The bringing of the liquid to the mark is effected by removing the excess by means of a capillary. In many forms a thermometer forms part of the apparatus.

Another type of vessel, named the Sprengel tube or pycnometer (Gr. [Greek: pyknos], dense), is shown in fig. 3. It consists of a cylindrical tube of a capacity ranging from 10 to 50 cc., provided at the upper end with a thick-walled capillary bent as shown on the left of the figure. From the bottom there leads another fine tube, bent upwards, and then at right angles so as to be at the same level as the capillary branch. This tube bears a graduation. A loop of platinum wire passed under these tubes serves to suspend the vessel from the balance arm. The manner of cleansing, &c., is the same as in the ordinary form. The vessel is filled by placing the capillary in a vessel containing the liquid and gently aspirating. Care must be taken that no air bubbles are enclosed. The liquid is adjusted to the mark by withdrawing any excess from the capillary end by a strip of bibulous paper or by a capillary tube. Many variations of this apparatus are in use; in one of the commonest there are two cylindrical chambers, joined at the bottom, and each provided at the top with fine tubes bent at right angles; sometimes the inlet and outlet tubes are provided with caps.



The specific gravity bottle may be used to determine the relative density of a solid which is available in small fragments, and is insoluble in the standard liquid. The method involves three operations:—(1) weighing the solid in air (W), (2) weighing the specific gravity bottle full of liquid (W1), (3) weighing the bottle containing the solid and filled up with liquid (W2). It is readily seen that W + W1 - W2 is the weight of the liquid displaced by the solid, and therefore is the weight of an equal volume of liquid; hence the relative density is W/(W + W1 - W2).

The determination of the absolute densities of gases can only be effected with any high degree of accuracy by a development of this method. As originated by Regnault, it consisted in filling a large glass globe with the gas by alternately exhausting with an air-pump and admitting the pure and dry gas. The flask was then brought to 0 by immersion in melting ice, the pressure of the gas taken, and the stop-cock closed. The flask is removed from the ice, allowed to attain the temperature of the room, and then weighed. The flask is now partially exhausted, transferred to the cooling bath, and after standing the pressure of the residual gas is taken by a manometer. The flask is again brought to room-temperature, and re-weighed. The difference in the weights corresponds to the volume of gas at a pressure equal to the difference of the recorded pressures. The volume of the flask is determined by weighing empty and filled with water. This method has been refined by many experimenters, among whom we may notice Morley and Lord Rayleigh. Morley determined the densities of hydrogen and oxygen in the course of his classical investigation of the composition of water. The method differed from Regnault's inasmuch as the flask was exhausted to an almost complete vacuum, a performance rendered possible by the high efficiency of the modern air-pump. The actual experiment necessitates the most elaborate precautions, for which reference must be made to Morley's original papers in the Smithsonian Contributions to Knowledge (1895), or to M. Travers, The Study of Gases. Lord Rayleigh has made many investigations of the absolute densities of gases, one of which, namely on atmospheric and artificial nitrogen, undertaken in conjunction with Sir William Ramsay, culminated in the discovery of argon (q.v.). He pointed out in 1888 (Proc. Roy. Soc. 43, p. 361) an important correction which had been overlooked by previous experimenters with Regnault's method, viz. the change in volume of the experimental globe due to shrinkage under diminished pressure; this may be experimentally determined and amounts to between 0.04 and 0.16% of the volume of the globe.

Related to the determination of the density of a gas is the determination of the density of a vapour, i.e. matter which at ordinary temperatures exists as a solid or liquid. This subject owes its importance in modern chemistry to the fact that the vapour density, when hydrogen is taken as the standard, gives perfectly definite information as to the molecular condition of the compound, since twice the vapour density equals the molecular weight of the compound. Many methods have been devised. In historical order we may briefly enumerate the following:—in 1811, Gay-Lussac volatilized a weighed quantity of liquid, which must be readily volatile, by letting it rise up a short tube containing mercury and standing inverted in a vessel holding the same metal. This method was developed by Hofmann in 1868, who replaced the short tube of Gay-Lussac by an ordinary barometer tube, thus effecting the volatilization in a Torricellian vacuum. In 1826 Dumas devised a method suitable for substances of high boiling-point; this consisted in its essential point in vaporizing the substance in a flask made of suitable material, sealing it when full of vapour, and weighing. This method is very tedious in detail. H. Sainte-Claire Deville and L. Troost made it available for specially high temperatures by employing porcelain vessels, sealing them with the oxyhydrogen blow-pipe, and maintaining a constant temperature by a vapour bath of mercury (350), sulphur (440), cadmium (860) and zinc (1040). In 1878 Victor Meyer devised his air-expulsion method.

Before discussing the methods now used in detail, a summary of the conclusions reached by Victor Meyer in his classical investigations in this field as to the applicability of the different methods will be given:

(1) For substances which do not boil higher than 260 and have vapours stable for 30 above the boiling-point and which do not react on mercury, use Victor Meyer's "mercury expulsion method."

(2) For substances boiling between 260 and 420, and which do not react on metals, use Meyer's "Wood's alloy expulsion method."

(3) For substances boiling at higher temperatures, or for any substance which reacts on mercury, Meyer's "air expulsion method" must be used. It is to be noted, however, that this method is applicable to substances of any boiling-point (see below).

(4) For substances which can be vaporized only under diminished pressure, several methods may be used. (a) Hofmann's is the best if the substance volatilizes at below 310, and does not react on mercury; otherwise (b) Demuth and Meyer's, Eykman's, Schall's, or other methods may be used.

1. Meyer's "Mercury Expulsion" Method.—A small quantity of the substance is weighed into a tube, of the form shown in fig. 4, which has a capacity of about 35 cc., provided with a capillary tube at the top, and a bent tube about 6 mm. in diameter at the bottom. The vessel is completely filled with mercury, the capillary sealed, and the vessel weighed. The vessel is then lowered into a jacket containing vapour at a known temperature which is sufficient to volatilize the substance. Mercury is expelled, and when this expulsion ceases, the vessel is removed, allowed to cool, and weighed. It is necessary to determine the pressure exerted on the vapour by the mercury in the narrow limb; this is effected by opening the capillary and inclining the tube until the mercury just reaches the top of the narrow tube; the difference between the height of the mercury in the wide tube and the top of the narrow tube represents the pressure due to the mercury column, and this must be added to the barometric pressure in order to deduce the total pressure on the vapour.



The result is calculated by means of the formula:

W(1 + [alpha]t) 7,980,000 D = ———————————————————————————————————————-, (p + p1 - s)[m{1 + [beta](t - t0)} - m1{1 + [gamma](t - t0)}](1 + [gamma]t)

in which W = weight of substance taken; t = temperature of vapour bath; [alpha] = 0.00366 = temperature coefficient of gases; p = barometric pressure; p1 = height of mercury column in vessel; s = vapour tension of mercury at t; m = weight of mercury contained in the vessel; m1 = weight of mercury left in vessel after heating; [beta] = coefficient of expansion of glass = .0000303; [gamma] = coefficient of expansion of mercury = 0.00018 (0.00019 above 240) (see Ber. 1877, 10, p. 2068; 1886, 19, p. 1862).

2. Meyer's Wood's Alloy Expulsion Method.—This method is a modification of the one just described. The alloy used is composed of 15 parts of bismuth, 8 of lead, 4 of tin and 3 of cadmium; it melts at 70, and can be experimented with as readily as mercury. The cylindrical vessel is replaced by a globular one, and the pressure on the vapour due to the column of alloy in the side tube is readily reduced to millimetres of mercury since the specific gravity of the alloy at the temperature of boiling sulphur, 444 (at which the apparatus is most frequently used), is two-thirds of that of mercury (see Ber. 1876, 9, p. 1220).



3. Meyer's Air Expulsion Method.—The simplicity, moderate accuracy, and adaptability of this method to every class of substance which can be vaporized entitles it to rank as one of the most potent methods in analytical chemistry; its invention is indissolubly connected with the name of Victor Meyer, being termed "Meyer's method" to the exclusion of his other original methods. It consists in determining the air expelled from a vessel by the vapour of a given quantity of the substance. The apparatus is shown in fig. 5. A long tube (a) terminates at the bottom in a cylindrical chamber of about 100-150 cc. capacity. The top is fitted with a rubber stopper, or in some forms with a stop-cock, while a little way down there is a bent delivery tube (b). To use the apparatus, the long tube is placed in a vapour bath (c) of the requisite temperature, and after the air within the tube is in equilibrium, the delivery tube is placed beneath the surface of the water in a pneumatic trough, the rubber stopper pushed home, and observation made as to whether any more air is being expelled. If this be not so, a graduated tube (d) is filled with water, and inverted over the delivery tube. The rubber stopper is removed and the experimental substance introduced, and the stopper quickly replaced to the same extent as before. Bubbles are quickly disengaged and collect in the graduated tube. Solids may be directly admitted to the tube from a weighing bottle, while liquids are conveniently introduced by means of small stoppered bottles, or, in the case of exceptionally volatile liquids, by means of a bulb blown on a piece of thin capillary tube, the tube being sealed during the weighing operation, and the capillary broken just before transference to the apparatus. To prevent the bottom of the apparatus being knocked out by the impact of the substance, a layer of sand, asbestos or sometimes mercury is placed in the tube. To complete the experiment, the graduated tube containing the expelled air is brought to a constant and determinate temperature and pressure, and this volume is the volume which the given weight of the substance would occupy if it were a gas under the same temperature and pressure. The vapour density is calculated by the following formula:

W(1 + [alpha]t) x 587,780 D = ————————————-, (p - s)V

in which W = weight of substance taken, V = volume of air expelled, [alpha] = 1/273 = .003665, t and p = temperature and pressure at which expelled air is measured, and s = vapour pressure of water at t.

By varying the material of the bulb, this apparatus is rendered available for exceptionally high temperatures. Vapour baths of iron are used in connexion with boiling anthracene (335), anthraquinone (368), sulphur (444), phosphoruspentasulphide (518); molten lead may also be used. For higher temperatures the bulb of the vapour density tube is made of porcelain or platinum, and is heated in a gas furnace.



(4a) Hofmann's Method.—Both the modus operandi and apparatus employed in this method particularly recommend its use for substances which do not react on mercury and which boil in a vacuum at below 310. The apparatus (fig. 6) consists of a barometer tube, containing mercury and standing in a bath of the same metal, surrounded by a vapour jacket. The vapour is circulated through the jacket, and the height of the mercury read by a cathetometer or otherwise. The substance is weighed into a small stoppered bottle, which is then placed beneath the mouth of the barometer tube. It ascends the tube, the substance is rapidly volatilized, and the mercury column is depressed; this depression is read off. It is necessary to know the volume of the tube above the second level; this may most efficiently be determined by calibrating the tube prior to its use. Sir T. E. Thorpe employed a barometer tube 96 cm. long, and determined the volume from the closed end for a distance of about 35 mm. by weighing in mercury; below this mark it was calibrated in the ordinary way so that a scale reading gave the volume at once. The calculation is effected by the following formulae:—

760w(1 + 0.003665t) D = —————————-; 0.0012934 V B

h / h1 h2 B = ——————— - ( ——————— - —————— + s), 1 + 0.00018t1 1 + 0.00018t2 1 + 0.00018t /

in which w = weight of substance taken; t = temperature of vapour jacket; V = volume of vapour at t; h = height of barometer reduced to 0; t1 = temperature of air; h1 = height of mercury column below vapour jacket; t2 = temperature of mercury column not heated by vapour; h2 = height of mercury column within vapour jacket; s = vapour tension of mercury at t. The vapour tension of mercury need not be taken into account when water is used in the jacket.

(4b) Demuth and Meyer's Method.—The principle of this method is as follows:—In the ordinary air expulsion method, the vapour always mixes to some extent with the air in the tube, and this involves a reduction of the pressure of the vapour. It is obvious that this reduction may be increased by accelerating the diffusion of the vapour. This may be accomplished by using a vessel with a somewhat wide bottom, and inserting the substance so that it may be volatilized very rapidly, as, for example, in tubes of Wood's alloy, and by filling the tube with hydrogen. (For further details see Ber. 23, p. 311.)



We may here notice a modification of Meyer's process in which the increase of pressure due to the volatilization of the substance, and not the volume of the expelled air, is measured. This method has been developed by J. S. Lumsden (Journ. Chem. Soc. 1903, 83, p. 342), whose apparatus is shown diagrammatically in fig. 7. The vaporizing bulb A has fused about it a jacket B, provided with a condenser c. Two side tubes are fused on to the neck of A: the lower one leads to a mercury manometer M, and to the air by means of a cock C; the upper tube is provided with a rubber stopper through which a glass rod passes—this rod serves to support the tube containing the substance to be experimented upon, and so avoids the objection to the practice of withdrawing the stopper of the tube, dropping the substance in, and reinserting the stopper. To use the apparatus, a liquid of suitable boiling-point is placed in the jacket and brought to the boiling-point. All parts of the apparatus are open to the air, and the mercury in the manometer is adjusted so as to come to a fixed mark a. The substance is now placed on the support already mentioned, and the apparatus closed to the air by inserting the cork at D and turning the cock C. By turning or withdrawing the support the substance enters the bulb; and during its vaporization the free limb of the manometer is raised so as to maintain the mercury at a. When the volatilization is quite complete, the level is accurately adjusted, and the difference of the levels of the mercury gives the pressure exerted by the vapour. To calculate the result it is necessary to know the capacity of the apparatus to the mark a, and the temperature of the jacket.

Methods depending on the Principles of Hydrostatics.—Hydrostatical principles can be applied to density determinations in four typical ways: (1) depending upon the fact that the heights of liquid columns supported by the same pressure vary inversely as the densities of the liquids; (2) depending upon the fact that a body which sinks in a liquid loses a weight equal to the weight of liquid which it displaces; (3) depending on the fact that a body remains suspended, neither floating nor sinking, in a liquid of exactly the same density; (4) depending on the fact that a floating body is immersed to such an extent that the weight of the fluid displaced equals the weight of the body.

1. The method of balancing columns is of limited use. Two forms are recognized. In one, applicable only to liquids which do not mix, the two liquids are poured into the limbs of a U tube. The heights of the columns above the surface of junction of the liquids are inversely proportional to the densities of the liquids. In the second form, named after Robert Hare (1781-1858), professor of chemistry at the university of Pennsylvania, the liquids are drawn or aspirated up vertical tubes which have their lower ends placed in reservoirs containing the different liquids, and their upper ends connected to a common tube which is in communication with an aspirator for decreasing the pressure within the vertical tubes. The heights to which the liquids rise, measured in each case by the distance between the surfaces in the reservoirs and in the tubes, are inversely proportional to the densities.

2. The method of "hydrostatic weighing" is one of the most important. The principle may be thus stated: the solid is weighed in air, and then in water. If W be the weight in air, and W1 the weight in water, then W1 is always less than W, the difference W - W1 representing the weight of the water displaced, i.e. the weight of a volume of water equal to that of the solid. Hence W/(W - W1) is the relative density or specific gravity of the body. The principle is readily adapted to the determination of the relative densities of two liquids, for it is obvious that if W be the weight of a solid body in air, W1 and W2 its weights when immersed in the liquids, then W - W1 and W - W2 are the weights of equal volumes of the liquids, and therefore the relative density is the quotient (W - W1)/(W - W2). The determination in the case of solids lighter than water is effected by the introduction of a sinker, i.e. a body which when affixed to the light solid causes it to sink. If W be the weight of the experimental solid in air, w the weight of the sinker in water, and W1 the weight of the solid plus sinker in water, then the relative density is given by W/(W + w - W1). In practice the solid or plummet is suspended from the balance arm by a fibre—silk, platinum, &c.—and carefully weighed. A small stool is then placed over the balance pan, and on this is placed a beaker of distilled water so that the solid is totally immersed. Some balances are provided with a "specific gravity pan," i.e. a pan with short suspending arms, provided with a hook at the bottom to which the fibre may be attached; when this is so, the stool is unnecessary. Any air bubbles are removed from the surface of the body by brushing with a camel-hair brush; if the solid be of a porous nature it is desirable to boil it for some time in water, thus expelling the air from its interstices. The weighing is conducted in the usual way by vibrations, except when the weight be small; it is then advisable to bring the pointer to zero, an operation rendered necessary by the damping due to the adhesion of water to the fibre. The temperature and pressure of the air and water must also be taken.

There are several corrections of the formula [Delta] = W/(W - W_1) necessary to the accurate expression of the density. Here we can only summarize the points of the investigation. It may be assumed that the weighing is made with brass weights in air at t and p mm. pressure. To determine the true weight _in vacuo_ at 0, account must be taken of the different buoyancies, or losses of true weight, due to the different volumes of the solids and weights. Similarly in the case of the weighing in water, account must be taken of the buoyancy of the weights, and also, if absolute densities be required, of the density of water at the temperature of the experiment. In a form of great accuracy the absolute density [Delta](0/4) is given by

[Delta](0/4) = ([rho][alpha]W - [delta]W1)/(W - W1),

in which W is the weight of the body in air at t and p mm. pressure, W_1 the weight in water, atmospheric conditions remaining very nearly the same; [rho] is the density of the water in which the body is weighed, [alpha] is (1 + [alpha]t) in which a is the coefficient of cubical expansion of the body, and [delta] is the density of the air at t, p mm. Less accurate formulae are [Delta] = [rho] W/(W - W_1), the factor involving the density of the air, and the coefficient of the expansion of the solid being disregarded, and [Delta] = W/(W - W_1), in which the density of water is taken as unity. Reference may be made to J. Wade and R. W. Merriman, _Journ. Chem. Soc._ 1909, 95, p. 2174.

The determination of the density of a liquid by weighing a plummet in air, and in the standard and experimental liquids, has been put into a very convenient laboratory form by means of the apparatus known as a Westphal balance (fig. 8). It consists of a steelyard mounted on a fulcrum; one arm carries at its extremity a heavy bob and pointer, the latter moving along a scale affixed to the stand and serving to indicate when the beam is in its standard position. The other arm is graduated in ten divisions and carries riders—bent pieces of wire of determined weights—and at its extremity a hook from which the glass plummet is suspended. To complete the apparatus there is a glass jar which serves to hold the liquid experimented with. The apparatus is so designed that when the plummet is suspended in air, the index of the beam is at the zero of the scale; if this be not so, then it is adjusted by a levelling screw. The plummet is now placed in distilled water at 15, and the beam brought to equilibrium by means of a rider, which we shall call 1, hung on a hook; other riders are provided, {1/10}th and {1/100}th respectively of 1. To determine the density of any liquid it is only necessary to suspend the plummet in the liquid, and to bring the beam to its normal position by means of the riders; the relative density is read off directly from the riders.



3. Methods depending on the free suspension of the solid in a liquid of the same density have been especially studied by Retgers and Gossner in view of their applicability to density determinations of crystals. Two typical forms are in use; in one a liquid is prepared in which the crystal freely swims, the density of the liquid being ascertained by the pycnometer or other methods; in the other a liquid of variable density, the so-called "diffusion column," is prepared, and observation is made of the level at which the particle comes to rest. The first type is in commonest use; since both necessitate the use of dense liquids, a summary of the media of most value, with their essential properties, will be given.

_Acetylene tetrabromide_, C_{2}H_{2}Br_4, which is very conveniently prepared by passing acetylene into cooled bromine, has a density of 3.001 at 6 C. It is highly convenient, since it is colourless, odourless, very stable and easily mobile. It may be diluted with benzene or toluene.

Methylene iodide, CH{2}I2, has a density of 3.33, and may be diluted with benzene. Introduced by Brauns in 1886, it was recommended by Retgers. Its advantages rest on its high density and mobility; its main disadvantages are its liability to decomposition, the originally colourless liquid becoming dark owing to the separation of iodine, and its high coefficient of expansion. Its density may be raised to 3.65 by dissolving iodoform and iodine in it.

Thoulet's solution, an aqueous solution of potassium and mercuric iodides (potassium iodo-mercurate), introduced by Thoulet and subsequently investigated by V. Goldschmidt, has a density of 3.196 at 22.9. It is almost colourless and has a small coefficient of expansion; its hygroscopic properties, its viscous character, and its action on the skin, however, militate against its use. A. Duboin (Compt. rend., 1905, p. 141) has investigated the solutions of mercuric iodide in other alkaline iodides; sodium iodo-mercurate solution has a density of 3.46 at 26, and gives with an excess of water a dense precipitate of mercuric iodide, which dissolves without decomposition in alcohol; lithium iodo-mercurate solution has a density of 3.28 at 25.6; and ammonium iodo-mercurate solution a density of 2.98 at 26.

Rohrbach's solution, an aqueous solution of barium and mercuric iodides, introduced by Carl Rohrbach, has a density of 3.588.

_Klein's solution_, an aqueous solution of cadmium borotungstate, 2Cd(OH)_{2}B_{2}O_{3}9WO_{3}16H_{2}O, introduced by D. Klein, has a density up to 3.28. The salt melts in its water of crystallization at 75, and the liquid thus obtained goes up to a density of 3.6.

Silver-thallium nitrate, TIAg(NO3)2, introduced by Retgers, melts at 75 to form a clear liquid of density 4.8; it may be diluted with water.

The method of using these liquids is in all cases the same; a particle is dropped in; if it floats a diluent is added and the mixture well stirred. This is continued until the particle freely swims, and then the density of the mixture is determined by the ordinary methods (see MINERALOGY).

In the "diffusion column" method, a liquid column uniformly varying in density from about 3.3 to 1 is prepared by pouring a little methylene iodide into a long test tube and adding five times as much benzene. The tube is tightly corked to prevent evaporation, and allowed to stand for some hours. The density of the column at any level is determined by means of the areometrical beads proposed by Alexander Wilson (1714-1786), professor of astronomy at Glasgow University. These are hollow glass beads of variable density; they may be prepared by melting off pieces of very thin capillary tubing, and determining the density in each case by the method just previously described. To use the column, the experimental fragment is introduced, when it takes up a definite position. By successive trials two beads, of known density, say d1, d2, are obtained, one of which floats above, and the other below, the test crystal; the distances separating the beads from the crystal are determined by means of a scale placed behind the tube. If the bead of density d1 be at the distance l1 above the crystal, and that of d2 at l2 below, it is obvious that if the density of the column varies uniformly, then the density of the test crystal is (d{1}l2 + d{2}l1)/(l1 + l2).

Acting on a principle quite different from any previously discussed is the capillary hydrometer or staktometer of Brewster, which is based upon the difference in the surface tension and density of pure water, and of mixtures of alcohol and water in varying proportions.

If a drop of water be allowed to form at the extremity of a fine tube, it will go on increasing until its weight overcomes the surface tension by which it clings to the tube, and then it will fall. Hence any impurity which diminishes the surface tension of the water will diminish the size of the drop (unless the density is proportionately diminished). According to Quincke, the surface tension of pure water in contact with air at 20 C. is 81 dynes per linear centimetre, while that of alcohol is only 25.5 dynes; and a small percentage of alcohol produces much more than a proportional decrease in the surface tension when added to pure water. The capillary hydrometer consists simply of a small pipette with a bulb in the middle of the stem, the pipette terminating in a very fine capillary point. The instrument being filled with distilled water, the number of drops required to empty the bulb and portions of the stem between two marks m and n (fig. 9) on the latter is carefully counted, and the experiments repeated at different temperatures. The pipette having been carefully dried, the process is repeated with pure alcohol or with proof spirits, and the strength of any admixture of water and spirits is determined from the corresponding number of drops, but the formula generally given is not based upon sound data. Sir David Brewster found with one of these instruments that the number of drops of pure water was 734, while of proof spirit, sp. gr. 920, the number was 2117.



REFERENCES.—Density and density determinations are discussed in all works on practical physics; reference may be made to B. Stewart and W. W. Haldane Gee, Practical Physics, vol. i. (1901); Kohlrausch, Practical Physics; Ostwald, Physico-Chemical Measurements. The density of gases is treated in M. W. Travers, The Experimental Study of Gases (1901); and vapour density determinations in Lassar-Cohn's Arbeitsmethoden fr organisch-chemische Laboratorien (1901), and Manual of Organic Chemistry (1896), and in H. Biltz, Practical Methods for determining Molecular Weights (1899). (C. E.*)



DENTATUS, MANIUS CURIUS, Roman general, conqueror of the Samnites and Pyrrhus, king of Epirus, was born of humble parents, and was possibly of Sabine origin. He is said to have been called Dentatus because he was born with his teeth already grown (Pliny, Nat. Hist. vii. 15). Except that he was tribune of the people, nothing certain is known of him until his first consulship in 290 B.C. when, in conjunction with his colleague P. Cornelius Rufinus, he gained a decisive victory over the Samnites, which put an end to a war that had lasted fifty years. He also reduced the revolted Sabines to submission; a large portion of their territory was distributed among the Roman citizens, and the most important towns received the citizenship without the right of voting for magistrates (civitas sine suffragio). With the proceeds of the spoils of the war Dentatus cut an artificial channel to carry off the waters of Lake Velinus, so as to drain the valley of Reate. In 275, after Pyrrhus had returned from Sicily to Italy, Dentatus (again consul) took the field against him. The decisive engagement took place near Beneventum in the Campi Arusini, and resulted in the total defeat of Pyrrhus. Dentatus celebrated a magnificent triumph, in which for the first time a number of captured elephants were exhibited. Dentatus was consul for the third time in 274, when he finally crushed the Lucanians and Samnites, and censor in 272. In the latter capacity he began to build an aqueduct to carry the waters of the Anio into the city, but died (270) before its completion. Dentatus was looked upon as a model of old Roman simplicity and frugality. According to the well-known anecdote, when the Samnites sent ambassadors with costly presents to induce him to exercise his influence on their behalf in the senate, they found him sitting on the hearth and preparing his simple meal of roasted turnips. He refused their gifts, saying that earthen dishes were good enough for him, adding that he preferred ruling those who possessed gold to possessing it himself. It is also said that he died so poor that the state was obliged to provide dowries for his daughters. But these and similar anecdotes must be received with caution, and it should be remembered that what was a competence in his day would have been considered poverty by the Romans of later times.

Livy, epitome, 11-14; Polybius ii. 19; Eutropius ii. 9, 14; Florus i. 18; Val. Max. iv. 3, 5, vi. 3, 4; Cicero, De senectute, 16; Juvenal xi. 78; Plutarch, Pyrrhus, 25.



DENTIL (from Lat. dens, a tooth), in architecture, a small tooth-shaped block used as a repeating ornament in the bed-mould of a cornice. Vitruvius (iv. 2) states that the dentil represents the end of a rafter (asser); and since it occurs in its most pronounced form in the Ionic temples of Asia Minor, the Lycian tombs and the porticoes and tombs of Persia, where it represents distinctly the reproduction in stone of timber construction, there is but little doubt as to its origin. The earliest example is that found on the tomb of Darius, c. 500 B.C., cut in the rock in which the portico of his palace is reproduced. Its first employment in Athens is in the cornice of the caryatid portico or tribune of the Erechtheum (480 B.C.). When subsequently introduced into the bed-mould of the cornice of the choragic monument of Lysicrates it is much smaller in its dimensions. In the later temples of Ionia, as in the temple of Priene, the larger scale of the dentil is still retained. As a general rule the projection of the dentil is equal to its width, and the intervals between to half the width. In some cases the projecting band has never had the sinkings cut into it to divide up the dentils, as in the Pantheon at Rome, and it is then called a dentil-band. The dentil was the chief decorative feature employed in the bed-mould by the Romans and the Italian Revivalists. In the porch of the church of St John Studius at Constantinople, the dentil and the interval between are equal in width, and the interval is splayed back from top to bottom; this is the form it takes in what is known as the "Venetian dentil," which was copied from the Byzantine dentil in Santa Sophia, Constantinople. There, however, it no longer formed part of a bed-mould: its use at Santa Sophia was to decorate the projecting moulding enclosing the encrusted marbles, and the dentils were cut alternately on both sides of the moulding. The Venetian dentil was also introduced as a label round arches and as a string course.



DENTISTRY

Historical sketch.

(from Lat. dens, a tooth), a special department of medical science, embracing the structure, function and therapeutics of the mouth and its contained organs, specifically the teeth, together with their surgical and prosthetic treatment. (For the anatomy of the teeth see TEETH.) As a distinct vocation it is first alluded to by Herodotus (500 B.C.). There are evidences that at an earlier date the Egyptians and Hindus attempted to replace lost teeth by attaching wood or ivory substitutes to adjacent sound teeth by means of threads or wires, but the gold fillings reputed to have been found in the teeth of Egyptian mummies have upon investigation been shown to be superficial applications of gold leaf for ornamental purposes. The impetus given to medical study in the Grecian schools by the followers of Aesculapius and especially Hippocrates (500 to 400 B.C.) developed among the practitioners of medicine and surgery considerable knowledge of dentistry. Galen (A.D. 131) taught that the teeth were true bones existing before birth, and to him is credited the belief that the upper canine teeth receive branches from the nerve which supplies the eye, and hence should be called "eye-teeth." Abulcasis (10th cent. A.D.) describes the operation by which artificial crowns are attached to adjacent sound teeth. Vesalius (1514), Ambroise Par, J. J. Scaliger, T. Kerckring, M. Malpighi, and lesser anatomists of the same period contributed dissertations which threw some small amount of light upon the structure and functions of the teeth. The operation of transplanting teeth is usually attributed to John Hunter (1728-1793), who practised it extensively, and gave to it additional prominence by transplanting a human tooth to the comb of a cock, but the operation was alluded to by Ambroise Par (1509-1590), and there is evidence to show that it was practised even earlier. A. von Leeuwenhoek in 1678 described with much accuracy the tubular structure of the dentine, thus making the most important contribution to the subject which had appeared up to that time. Until the latter part of the 18th century extraction was practically the only operation for the cure of toothache.

The early contributions of France exerted a controlling influence upon the development of dental practice. Urbain Hmard, surgeon to the cardinal Georges of Armagnac, whom Dr Blake (1801) calls an ingenious surgeon and a great man, published in 1582 his Researches upon the Anatomy of the Teeth, their Nature and Properties. Of Hmard, M. Fauchard says: "This surgeon had read Greek and Latin authors, whose writings he has judiciously incorporated in his own works." In 1728 Fauchard, who has been called the father of modern dentistry, published his celebrated work, entitled Le Chirurgien Dentiste ou trait des dents. The preface contains the following statement as to the existing status of dental art and science in France, which might have been applied with equal truth to any other European country:—" The most celebrated surgeons having abandoned this branch of surgery, or having but little cultivated it, their negligence gave rise to a class of persons who, without theoretic knowledge or experience, and without being qualified, practised it at hazard, having neither principles nor system. It was only since the year 1700 that the intelligent in Paris opened their eyes to these abuses, when it was provided that those who intended practising dental surgery should submit to an examination by men learned in all the branches of medical science, who should decide upon their merits." After the publication of Fauchard's work the practice of dentistry became more specialized and distinctly separated from medical practice, the best exponents of the art being trained as apprentices by practitioners of ability, who had acquired their training in the same way from their predecessors. Fauchard suggested porcelain as an improvement upon bone and ivory for the manufacture of artificial teeth, a suggestion which he obtained from R. A. F. de Raumur, the French savant and physicist, who was a contributor to the royal porcelain manufactory at Svres. Later, Duchateau, an apothecary of St Germain, made porcelain teeth, and communicated his discovery to the Academy of Surgery in 1776, but kept the process secret. Du Bois Chmant carried the art to England, and the process was finally made public by M. Du Bois Foucou. M. Fonzi improved the art to such an extent that the Athenaeum of Arts in Paris awarded him a medal and crown (March 14, 1808).

In Great Britain the 19th century brought the dawning of dental science. The work of Dr Blake in 1801 on the anatomy of the teeth was distinctly in advance of anything previously written on the subject. Joseph Fox was one of the first members of the medical profession to devote himself exclusively to dentistry, and his work is a repository of the best practice of his time. The processes described, though comparatively crude, involve principles in use at the present time. Thomas Bell, the successor of Fox as lecturer on the structure and disease of the teeth at Guy's Hospital, published his well-known work in 1829. About this period numerous publications on dentistry made their appearance, notably those of Koecker, Johnson and Waite, followed somewhat later by the admirable work of Alexander Nasmyth (1839). By this time Cuvier, Serres, Rousseau, Bertin, Herissant and others in France had added to the knowledge of human and comparative dental anatomy, while M. G. Retzius, of Sweden, and E. H. Weber, J. C. Rosenmller, Schreger, J. E. von Purkinje, B. Fraenkel and J. Mller in Germany were carrying forward the same lines of research. The sympathetic nervous relationships of the teeth with other parts of the body, and the interaction of diseases of the teeth with general pathological conditions, were clearly established. Thus a scientific foundation was laid, and dentistry came to be practised as a specialty of medicine. Certain minor operations, however, such as the extraction of teeth and the stopping of caries in an imperfect way, were still practised by barbers, and the empirical practice of dentistry, especially of those operations which were almost wholly mechanical, had developed a considerable body of dental artisans who, though without medical education in many cases, possessed a high degree of manipulative skill. Thus there came to be two classes of practitioners, the first regarding dentistry as a specialty of medicine, the latter as a distinct and separate calling.

In America representatives of both classes of dentists began to arrive from England and France about the time of the Revolution. Among these were John Wooffendale (1766), a student of Robert Berdmore of Liverpool, surgeon-dentist to George III.; James Gardette (1778), a French physician and surgeon; and Joseph Lemaire (1781), a French dentist who went out with the army of Count Rochambeau. During the winter of 1781-1782, while the Continental army was in winter quarters at Providence, Rhode Island, Lemaire found time and opportunity to practise his calling, and also to instruct one or two persons, notably Josiah Flagg, probably the first American dentist. Dental practice was thus established upon American soil, where it has produced such fertile results.

Course of training.

Until well into the 19th century apprenticeship afforded the only means of acquiring a knowledge of dentistry. The profits derived from the apprenticeship system fostered secrecy and quackery among many of the early practitioners; but the more liberal minded and better educated of the craft developed an increasing opposition to these narrow methods. In 1837 a local association of dentists was formed in New York, and in 1840 a national association, The American Society of Dental Surgeons, the object of which was "to advance the science by free communication and interchange of sentiments." The first dental periodical in the world, The American Journal of Dental Science, was issued in June 1839, and in November 1840 was established the Baltimore College of Dental Surgery, the first college in the world for the systematic education of dentists. Thus the year 1839-1840 marks the birth of the three factors essential to professional growth in dentistry. All this, combined with the refusal of the medical schools to furnish the desired facilities for dental instruction, placed dentistry for the time being upon a footing entirely separate from general medicine. Since then the curriculum of study preparatory to dental practice has been systematically increased both as to its content and length, until in all fundamental principles it is practically equal to that required for the training of medical specialists, and in addition includes the technical subjects peculiar to dentistry. In England, and to some extent upon the continent, the old apprenticeship system is retained as an adjunct to the college course, but it is rapidly dying out, as it has already done in America. Owing to the regulation by law of the educational requirements, the increase of institutions devoted to the professional training of dentists has been rapid in all civilized countries, and during the past twenty years especially so in the United States. Great Britain possesses upwards of twelve institutions for dental instruction, France two, Germany and Switzerland six, all being based upon the conception that dentistry is a department of general medicine. In the United States there were in 1878 twelve dental schools, with about 700 students; in 1907 there were fifty-seven schools, with 6919 students. Of these fifty-seven schools, thirty-seven are departments of universities or of medical institutions, and there is a growing tendency to regard dentistry from its educational aspect as a special department of the general medical and surgical practice.

Research.

Recent studies have shown that besides being an important part of the digestive system, the mouth sustains intimate relationship with the general nervous system, and is important as the portal of entrance for the majority of the bacteria that cause specific diseases. This fact has rendered more intimate the relations between dentistry and the general practice of medicine, and has given a powerful impetus to scientific studies in dentistry. Through the researches of Sir J. Tomes, Mummery, Hopewell Smith, Williams and others in England, O. Hertwig, Weil and Rse in Germany, Andrews, Sudduth and Black in America, the minute anatomy and embryology of the dental tissues have been worked out with great fulness and precision. In particular, it has been demonstrated that certain general systemic diseases have a distinct oral expression. Through their extensive nervous connexions with the largest of the cranial nerves and with the sympathetic nervous system, the teeth frequently cause irritation resulting in profound reflex nervous phenomena, which are curable only by removal of the local tooth disorder. Gout, lithaemia, scurvy, rickets, lead and mercurial poisoning, and certain forms of chronic nephritis, produce dental and oral lesions which are either pathognomonic or strongly indicative of their several constitutional causes, and are thus of great importance in diagnosis. The most important dental research of modern times is that which was carried out by Professor W. D. Miller of Berlin (1884) upon the cause of caries of the teeth, a disease said to affect the human race more extensively than any other. Miller demonstrated that, as previous observers had suspected, caries is of bacterial origin, and that acids play an important rle in the process. The disease is brought about by a group of bacteria which develop in the mouth, growing naturally upon the dbris of starchy or carbohydrate food, producing fermentation of the mass, with lactic acid as the end product. The lactic acid dissolves the mineral constituent of the tooth structure, calcium phosphate, leaving the organic matrix of the tooth exposed. Another class of germs, the peptonising and putrefactive bacteria, then convert the organic matter into liquid or gaseous end products. The accuracy of the conclusions obtained from his analytic research was synthetically proved, after the manner of Koch, by producing the disease artificially. Caries of the teeth has been shown to bear highly important relation to more remote or systemic diseases. Exposure and death of the dental pulp furnishes an avenue of entrance for disease-producing bacteria, by which invasion of the deeper tissues may readily take place, causing necrosis, tuberculosis, actinomycosis, phlegmon and other destructive inflammations, certain of which, affecting the various sinuses of the head, have been found to cause meningitis, chronic empyema, metastatic abscesses in remote parts of the body, paralysis, epilepsy and insanity.

Filling or stopping.

Operative Dentistry.—The art of dentistry is usually divided arbitrarily into operative dentistry, the purpose of which is to preserve as far as possible the teeth and associated tissues, and prosthetic dentistry, the purpose of which is to supply the loss of teeth by artificial substitutes. The filling of carious cavities was probably first performed with lead, suggested apparently by an operation recorded by Celsus (100 B.C.), who recommended that frail or decayed teeth be stuffed with lead previous to extraction, in order that they might not break under the forceps. The use of lead as a filling was sufficiently prevalent in France during the 17th century to bring into use the word plombage, which is still occasionally applied in that country to the operation of filling. Gold as a filling material came into general use about the beginning of the 19th century.[1] The earlier preparations of gold were so impure as to be virtually without cohesion, so that they were of use only in cavities which had sound walls for its retention. In the form of rolls or tape it was forced into the previously cleaned and prepared cavity, condensed with instruments under heavy hand pressure, smoothed with files, and finally burnished. Tin foil was also used to a limited extent and by the same method. Improvements in the refining of gold for dental use brought the product to a fair degree of purity, and, about 1855, led to the invention by Dr Robert Arthur of Baltimore of a method by which it could be welded firmly within the cavity. The cohesive properties of the foil were developed by passing it through an alcohol flame, which dispelled its surface contaminations. The gold was then welded piece by piece into a homogeneous mass by plugging instruments with serrated points. In this process of cold-welding, the mallet, hitherto in only limited use, was found more efficient than hand pressure, and was rapidly developed. The primitive mallet of wood, ivory, lead or steel, was supplanted by a mallet in which a hammer was released automatically by a spring condensed by pressure of the operator's hand. Then followed mallets operated by pneumatic pressure, by the dental engine, and finally by the electro-magnet, as utilized in 1867 by Bonwill. These devices greatly facilitated the operation, and made possible a partial or entire restoration of the tooth-crown in conformity with anatomical lines.

The dental engine in its several forms is the outgrowth of the simple drill worked by the hand of the operator. It is used in removing decayed structure and for shaping the cavity for inserting the filling. From time to time its usefulness has been extended, so that it is now used for finishing fillings and polishing them, for polishing the teeth, removing deposits from them and changing their shapes. Its latest development, the dento-surgical engine, is of heavier construction and is adapted to operations upon all of the bones, a recent addition to its equipment being the spiral osteotome of Cryer, by which, with a minimum shock to the patient, fenestrae of any size or shape in the brain-case may be made, from a simple trepanning operation to the more extensive openings required in intra-cranial operations. The rotary power may be supplied by the foot of the operator, or by hydraulic or electric motors. The rubber dam invented by S. C. Barnum of New York (1864) provided a means for protecting the field of operations from the oral fluids, and extended the scope of operations even to the entire restoration of tooth-crowns with cohesive gold foil. Its value has been found to be even greater than was at first anticipated. In all operations involving the exposed dental pulp or the pulp-chamber and root-canals, it is the only efficient method of mechanically protecting the field of operation from invasion by disease-producing bacteria.

The difficulty and annoyance attending the insertion of gold, its high thermal conductivity, and its objectionable colour have led to an increasing use of amalgam, guttapercha, and cements of zinc oxide mixed with zinc chloride or phosphoric acid. Recently much attention has been devoted to restorations with porcelain. A piece of platinum foil of .001 inch thickness is burnished and pressed into the cavity, so that a matrix is produced exactly fitting the cavity. Into this matrix is placed a mixture of powdered porcelain and water or alcohol, of the colour to match the tooth. The mass is carefully dried and then fused until homogeneous. Shrinkage is counteracted by additions of porcelain powder, which are repeatedly fused until the whole exactly fills the matrix. After cooling, the matrix is stripped away and the porcelain is cemented into the cavity. When the cement has hardened, the surface of the porcelain is ground and polished to proper contour. If successfully made, porcelain fillings are scarcely noticeable. Their durability remains to be tested.

Dental therapeutics.

Until recent times the exposure of the dental pulp inevitably led to its death and disintegration, and, by invasion of bacteria via the pulp canal, set up an inflammatory process which eventually caused the loss of the entire tooth. A rational system of therapeutics, in conjunction with proper antiseptic measures, has made possible both the conservative treatment of the dental pulp when exposed, and the successful treatment of pulp-canals when the pulp has been devitalized either by design or disease. The conservation of the exposed pulp is affected by the operation of capping. In capping a pulp, irritation is allayed by antiseptic and sedative treatment, and a metallic cap, lined with a non-irritant sedative paste, is applied under aseptic conditions immediately over the point of pulp exposure. A filling of cement is superimposed, and this, after it has hardened, is covered with a metallic or other suitable filling. The utility of arsenious acid for devitalizing the dental pulp was discovered by J. R. Spooner of Montreal, and first published in 1836 by his brother Shearjashub in his Guide to Sound Teeth. The painful action of arsenic upon the pulp was avoided by the addition of various sedative drugs,—morphia, atropia, iodoform, &c.,—and its use soon became universal. Of late years it is being gradually supplanted by immediate surgical extirpation under the benumbing effect of cocaine salts. By the use of cocaine also the pain incident to excavating and shaping of cavities in tooth structure may be controlled, especially when the cocaine is driven into the dentine by means of an electric current. To fill the pulp-chamber and canals of teeth after loss of the pulp, all organic remains of pulp tissue should be removed by sterilization, and then, in order to prevent the entrance of bacteria, and consequent infection, the canals should be perfectly filled. Upon the exclusion of infection depends the future integrity and comfort of the tooth. Numberless methods have been invented for the operation. Pulpless teeth are thus preserved through long periods of usefulness, and even those remains of teeth in which the crowns have been lost are rendered comfortable and useful as supports for artificial crowns, and as abutments for assemblages of crowns, known as bridge-work.