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OR, A

DICTIONARY

O F

ARTS, SCIENCES,

AND

MISCELLANEOUS LITERATURE;
Conftructed on a PLAN,

BY WHICн

THE DIFFERENT SCIENCES AND ARTS
Are digefted into the FORM of Distinct

TREATISES

OR

COMPREHENDING

SYSTEMS,

The HISTORY, THEORY, and PRACTICE, of each,
according to the Latest Discoveries and Improvements;

AND FULL EXPLANATIONS GIVEN OF THE

VARIOUS DETACHED PARTS OF KNOWLEDGE,

WHETHER RELATING TO

NATURAL and ARTIFICIAL Objects, or to Matters ECCLESIASTICAL,
CIVIL, MILITARY, COMMERCIAL, &'C.

Including ELUCIDATIONS of the most important Topics relative to RELIGION, MORALS,
MANNERS, and the OECONOMY of LIFE:

TOGETHER WITH

A DESCRIPTION of all the Countries, Cities, principal Mountains, Seas, Rivers, &c.
throughout the WORLD;

A General HISTORY, Ancient and Modern, of the different Empires, Kingdoms, and States;

AND

An Account of the LIVES of the most Eminent Perfons in every Nation,

from the earlieft ages down to the prefent times.

Compiled from the writings of the beft Authors, in feveral languages; the most approved Dictionaries, as well of general fcience as of its parti
cular branches; the Tranfuctions, Journals, and Memoirs, of Learned Societies, both at home and abroad; the MS. Lectures of
Eminent Profeffors on different sciences; and a variety of Original Materials, furnifced by an Extenfive Correspondence.

THE THIRD EDITION, IN EIGHTEEN VOLUMES, GREATLY IMPROVED.

ILLUSTRATED WITH FIVE HUNDRED AND FORTY-TWO COPPERPLATES.
VOL. VI.

INDOCTI DISCANT, ET AMENT MEMINISSE PERIT 1.

EDINBURGH,

PRINTED FOR A. BELL AND C. MACFARQUHAR

MDCCXCVII,

Entered in Stationers Hall in Terms of the A&t of Parliament.

ENCYCLOPEDIA BRITANNICA.

Diamond.

DIA
IAMOND, a genus of earths of the filiceous kind,
called Adamas Gemma by the Latins, Demant
by the Germans and Swedes, and Diamant by the
French, is the hardest of all ftones hitherto discovered;
commonly clear or tranfparent; though this property
may perhaps belong only to the cryftals, and not to
the rock from which they originate. When brought
to Europe in its rough ftate, it is either in the form of
roundish pebbles, with fhining furfaces, or of octoedral
crystals; but though they generally appear in octo-
dral forms, yet their cryftals are frequently irregular,
efpecially when the furface inclines to cryftallize du-
ring the fhooting of the whole cryftal, and alfo when
feveral of them unite in one group; in which cafe the
one hinders the other from affuming a regular form.
Mr Magellan, however, informs us, that diamonds
fometimes affume other forms. He has feen a rough
diamond in its native state, of a regular cubical form,
with its angles truncated or cut off; likewife ano-
ther belonging to Dr Combe of London, whofe fquare
fides were naturally joined by two very narrow long fa-
cets, forming angles of about 120 degrees; and the
corners were quite perfect.

Though the diamond is commonly clear and pellu-
cid, yet fome of them are met with of a rofe colour,
or inclining to green, blue, or black, and fome have
black specks. Tavernier faw one in the treafury of
the Mogul, with black specks in it, weighing about
56 carats; and he informs us, that yellow and black
diamonds are produced in the mines at Carnatica. Mr
Dutens alfo relates, that he faw a black diamond at
Vienna in the collection of the prince de Lichten-
ftein. Some diamonds have a greenish cruft; and of
these M. Tavernier relates, that they burst into pieces
while working into a proper fhape, or in the very act
of polishing on the wheel. In confirmation of this,
he mentions a large diamond worth upwards of 5000l.
Sterling, which burft into nine pieces while polishing
on the wheel at Venice.

The fineft diamonds are thofe of a complexion like that of a drop of pure water. It is likewife a valuable property if they are of a regular form and truly made; as alfo that they be free from ftains, fpots, fpecks, flaws, and crofs veins. If diamonds are tinctured yellow, blue, green, or red, in a high degree, they are next in efteem; but if they are tinctured with thefe colours only in a low degree, the value of them is greatly diminished. There are alfo diamonds of other complexions; fuch as brown, and thofe of a dark hue: the first refembling the browneft fugar-candy, and the latter dufky iron. In the Philofophical Commerce of Arts, Dr Lewis tells us of a black diamond that he himfelf had feen. At a diftance, it looked uniformly VOL. VI. Part I.

DIA

black; but on closer examination appeared in fome Diamond.
parts tranfparent, and in others charged with foulnefs,
on which the black hue depended.

Thefe gems are lamellated, confifting of very thin
plates like thofe of talc, but very clofely united; the
direction of which must be found out by lapidaries be-
fore they can work them properly: Such as have
their foliated fubftance not in a flat pofition, are called
by the workmen diamonds of nature.

The names of oriental and occidental, given by jewellers to this and all other precious ftones, have a different meaning from the obvious fenfe; the finest and hardeft being always called oriental, whether they be produced in the eaft or not. Thofe called occidental are of inferior value; but according to Mr Jefferies, who has written a treatife on the subject, the diamonds of Brafil equal the finest oriental ones. The art of cutting these gems was invented in 1476 by Louis de Berquen a native of Bruges in the Auftrian Netherlands. This ftone becomes luminous in the dark, by expofure during a certain time to the rays of the fun; by heating it in a crucible; by plunging it in boiling water; or by rubbing it with a piece of glass. By friction it acquires an electrical property, by which it attracts the fubftance ufed for foils called black maflic, and other light matters. The author of the Chemical Dictionary fays, that diamonds are refractory in the fire, and even apyrous. Nevertheless, experiments have been made, which prove that diamonds are capable of being diffipated, not only by the collected heat of the fun, but also by the heat of a furnace. Mr Boyle fays, that he perceived certain acrid and penetrating exhalations from diamonds expofed to fire. A diamond by expofure to a concave speculum, the diameter of which was 40 inches, was reduced to an eighth part of its weight*. In the Giornale de Letterati d'Italia, tom. viii. art. 9. we may read a relation of experiments made on precious ftones, by order of the grand duke of Tuscany, with a burning lens, the diameter of which was two thirds of a Florentine ell, near the focus of which was placed another fmaller lens. By these experiments we find, that diamonds were more altered by folar heat than most of the other precious ftones, although not the least appearance of a commencing fufion was obfervable. A diamond weighing 30 grains, thus expofed during 30 feconds, loft its colour, luftre, and tranfparency, and became of an opaque white. In five minutes, bubbles appeared on its furface; foon afterwards it burft into pieces, which were diffipated; and the fmall fragment which remained was capable of being crushed into fine powder by the preffure of the blade of a knife. Neither the addition of glafs, flints, fulphur, metals, or falt of tartar, prevented this diffi A

pation

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Plilof. Tranfac n° 386.

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