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lived at the same lime, and so were capable to converse together.Rut yet some good writers have run into the impropriety offeignmgdialogues between persons who lived at distant times. Plato took this method, in which he has been followed by Macrobius .Rut others, who have been willing to bring persons to discoursetogether, who lived in dili’ereiit ages, without such inconsistency,have wrote Dialogues of the Dead.
DIALTILFA, in pharmacy, an unguent much used as a resol-vent; so called from althxa, or marshmallows, which is the prin-cipal ingredient in it.
DIALYSIS, the figure in rhetoric by which syllables
or words are divided.
Di alysis, in grammar, a mark or character, consisting of twopoints (") placed over two vowels, because otherwise they wouldmake a diphthong, as Mosaic, Phaeton, See.
DIAMANT, a town of the island of A'Jartinico, on the southcoast.
DIAMASTIGOSIS, a festival at Sparta in honour of DianaOrthia, which received that name nm iov pari yow, from whipping,because boys were whipped before the altar of the goddess. Theseboys, called bomonicir, were originally free-born Spartans, but Intin: more delicate ages they were of mean birth, and generally of aslavish origin.
DIAMETER, [I** and fx.tr the line, which passing throughthe centre of a circle or other curvilinear figure, divides it intoequal parts.
Diamkter, in conic sections. See Conic Sections.
DIAMON D, [ diamant , Fr. adamas, Lat.] the most valuable andhardest of all the gems, is, when pure, perfectly clear and pellucid asthe purest w ater ; anti is eminently distinguished from all other sub-stances by its vivid splendour, and the brightness of its refections.It is extremely various in shape and size, being found in the great-est quantity very small, and the larger ones extremely seldommet with. But most commonly it is crystallized in the form of asix-sided prism, terminated by a six-sided pyramid. Its brilliancyarises from its greater refr ctive power, which is such as to causeall the light to he reflected which falls on it at au angle of inci-dence greater than 24*- degrees; and it is capable of being ren-dered still more brilliant by its surface being cut into facets, whichmultiply the reflections of light. From its hardness its lustre re-mains uninjured : this hardness is such, that it can be cut, or ra-ther worn dow n only by rubbing one diamond against another, and ispolished only'by the liner diamond powder. Diamonds are foundin India , in the districts of Visapore, Golcomla, Bengal, and theisland of Ceylon, and in Brazil in South America . It is not foundin its original situation, but in the beds of streams, or in a looseferruginous sand beneath the soil. The Brazilian diamonds areinferior in transparency and purity to the Oriental. The diamondis col airless, or tinged of various shades of wdiite or grey, andsometimes also, though more rarely, of brown, green, yellow,blue, and red, frequently with darker coloured spots. It is gene-rally transparent, though not perfectly so, and has the properly ofsingle refraction ; its fracture is lamellated, and it can be split bystriking it in the direction of the plates. Its specific gravity isfrom 3.‘>00 to 3d00. lt*is phosphorescent, or, when it has beenexposed to the light, is luminous in the dark. It is rendered elec-trical by rubbing, the electricity being positive. The diamondwas long thought to be an incombustible substance since it was foundto resist the action of the strongest fires. However, Sir Isaac Newton observing that combustibles refract light more powerfully than©tuer bodies, and that the'diamond possesses this property in greatperfection, suspected it, from that circumstance, to be capable ofcombustion. This singular conjecture was verified in 1694 by theFlorentine academicians, in the presence of Cosmo Ill. grandduke of Tuscany . By means of a burning-glass, they consumedseveral diamonds. Francis I. emperor of Germany , afterwardswitnessed the destruction of several more in the beat of the furnace.1 iiese experiments were repeated by Rouelle, Macqiier, andDarcct; who proved that the diamond was not merely evaporatedbut actually burnt; and that if air was excluded it underwent nochange. No attempt, however, was made to ascertain the producttill 1772. Lavoisier , in a memoir published that year, shewedthat when the diamond is burnt, carbonic acid gas is obtained, andthat there is a striking analogy between it and charcoal. In 178bGuyton-Morveau found that the diamond is combustible whendropped into melted nitre ; that it burns without leaving any resi-
duum, and in a manner analogous to charcoal. This experimentwas repeated with more precision by Mr. Tennant in 1797. Theconclusion which lie drew from it was, that when a diamond isburnt the whole of the product is carbonic acid gas: that a givenweight of diamond yields just as much carbonic acid gas as thesame weight of charcoal; arid "that diamond and charcoal are bothcomposed of the very same substance. 'S he conclusion that dia-mond is nothing else than charcoal, was directly contrary to w hatone would have expected from comparing the two substances to-gether.' Their colour, hardness, specific gravity, and electricalproperties, are exceedingly different; nor do they resemble eachother more nearly in their combustibility. Charcoal takes fire ata red heat; and when once kindled in oxygen gas continues toburn till it is wholly consumed. According to Morveau, the dia-mond, before it can be burnt, must be exposed to the sun’s raysin the focus of a large burning glass, or to a heat not under bOOOYBut Sir George M‘Kenzie found that diamonds will burn in amuffle, w hen heated no higher than 14° or 15° Wedgewood; whichmust be considerably lower than 5000° Fahrenheit. Its surfaceassumes a black colour like charcoal: this crust is soon wasted,and another is formed in its place. It was in this manner that adiamond weighing 3.089 grains troy, gradually wasted away com-pletely when- exposed by Morveau for one hour and forty mi-nutes in the focus of the celebrated burning glass of Tschirnhau-sen, while a thermometer exposed to the sun stood at 104°.Morveau found that one part of the diamond during its com-bustion combines with 4.592 parts of oxygen, and the carbonicacid gas formed amounts to 5.592 parts: consequently, carbonicacid gas is composed of one part of diamond and 4.592 ofoxygen; or, which is the same thing, 100 parts of carbonic acidgas are composed of
17.88 diamond
82.12 oxygen
100.00
But Lavoisier , ascertained that one part of charcoal, when burnt,combines with 2.5714 parts of oxygen, and forms 3.5714 parts ofcarbonic acid gas : consequently 100 parts of carbonic acid gas arecomposed of
28 charcoal72 oxygen
100 .
But 100 parts of carbonic acid gas are also composed of 17.88diamond, and 82.12 oxygen. \Ve have therefore this equation :
Diamond. Oxygen. Char. Oxygen.
17.88 + 82.12 = 28 -J- 72
Consequently, subtracting 72 parts of oxygen from both sides ofthe equation, we have
17.88 -f- 10.12 = 28 charcoal.
That is to say, 28 parts of charcoal are composed of 17.88 dia-mond and 10.12 oxygen. Of course, 100 parts of charcoal arecomposed of
63.85 diamond36.15 oxygen
100.00
The diamond, from these experiments, appears to be that sub-stance in a state of purity to which Lavoisier and his associatesgave the name of carbon; and therefore charcoal is notcarbon, as they supposed, but the oxide of carbon. Thus char-coal is a compound substance, and hence the different qualities ofcharcoal and carbon, or diamond. See Carbon. Sir GeorgeMackenzie , likewise, repeated and confirmed an experiment ofthe French chemists, in which a piece of soft iron was convertedinto steel by being heated with diamonds, in the same manner asit would have been by being heated in the usual manner withcharcoal powder; and his experiments are more satisfactory,as havingbeen made with a diamond in its purest state. (Nicholson’sJournal, 4to. vol. iv. p. 103.) The first water in diamonds meansthe greatest purity and perfection of their complexion, whichought to be that of the purest water. When diamonds‘‘iall shortof this perfection, they are said to be of the second or third water,
tkc.