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called Adamas Gemma by the Latins, Demant parts transparent, and in others charged with foulness,
water; or by rubbing it with a piece of glass. By
Tranfire, he mentions a large diamond worth upwards of 5000l. viii. art. 9. we may read a relation of experiments
no 386. Sterling, which burst into nine pieces while polishing made on precious stones, by order of the grand duke on the wheel at Venice.
of Tuscany, with a burning lens, the diameter of which The finest diamonds are those of a complexion like was two thirds of a Florentine ell, near the focus of that of a drop of pure water. It is likewise a valuable pro- which was placed another finaller lens. By these experty if they are of a regular form and truly made; as periments we find, that diamonds were more altered by also that they be free from stains, spots, specks, flaws, folar heat than moit of the other precious stones, aland cross veins. If diamonds are tinctured yellow, though not the leait appearance of a commencing fublue, green, or red, in a high degree, they are next fion was observable.
A diamond weighing 30 grains, in elteem; but if they are tinctured with these colours thus expofed during 30 seconds, lost its colour, luftre, only in a low degree, the value of them is greatly di- and transparency, and became of an opaque white. In minished. There are also diamonds of other com- five minutes, bubbles appeared on its surface; soon afplexions ; such as brown, and those of a dark hue: terwards it burft into pieces, which were dislipated; the first resembling the browneft sugar-cardy, and the and the small fragment which remained was capable of latter dusky iron. In the Philosophical Commerce of being crushed into tine powder by the presure of the Arts, Dr Lewis tells us of a black diamond that he blade of a knife. Neither the addition of glafi, flints, himself had seen. At a distance, it looked uniformly fulphur, metals, or falt of tartar, prevented this difii. Vol. VI. Part I.
Diamond. pation of diamonds, or occafioned any degree of fulion. which this fubftance defends metals from destruction by Diamonl.
By this heat rubies were softened, and lost some of fire. He was confirmed in his opinion, by observing
certain this question, M. Cadet exposed diamonds in Experiments were also made by order of the empe. covered and luted crucibles to the violent heat of a forge ror Francis I. on precious itones; from which we find, during two hours ; by which operation the diamonds that diamonds were entirely diffipated by having been loft only ifth part of their weight. He infers, that exposed in crucibles to a violent fire of a furnace du. the destruction of diamonds by fire in open vessels is ring 24 hours ; while rubies by the fame heat were not not a true volatilization ; but merely an exfoliation, altered in weight, colour, or polith. By expofing dia- caused by the fire expanding the air contained between monds during two hours only at a time, the following the thin plates of which these stones confit, and that alterations produced on them by fire were observed. by this exfoliation or decrepitation these plates are re. First, they loit their polish ; then they were split into duced to fo fine a powder as to escape observation. thin plates; and, lailly, totally diffipated. By the M. D'Arcet objected against the experiments of his fame fire, emeralds were fused. See Alagafin de Ham- adversaries, that they were not of sufficient duration to bourg, tom. xviii.
decide against his, which had lafted several days. He The action of fire on diamonds has, notwithstanding renewed and multiplied his experiments, which conthe above mentioned experiments, been lately doubted firmed him in his opinion of the volatilization of diain France; and the queition has been agitated by seve. monds in vessels perfectly closed ; and that this effect Tal eminent chemists with much interest, and numerous of fire on diamonds is not a mere exfoliation or mechaexperiments have been made which throw some light nical feparation of the plates of which these stones on the subject. M. D'Arcet found, not only that dia. confift, he infers from the parts of the diamonds permunds included in porcelain crucibles close, or covered vading the most folid porcelain crucibles without being with perforated lids, and exposed to the long and in- perceptible, and from the luminous appearance firit tense heat of a porcelain furnace, were perfectly diffi- noticed by M. Macquer, and which was afterwards obpated; but also, that these stones could in a few hours served by M. Roux to be an actual flame. be totally volatilised with a much inferior degree of Diamonds are found only in the East Indies, and in heat, by exposing them in a coppel, under the muffte Brasil in South America. The diamond mines are of an eslay-furnace. In this latter experiment, he ob- found only in the kingdoms of Golconda, Visapour, ferved that the diffipation was gradual, and that it was Bengal, and the island of Borneo. There are four effected by a kind of exfoliation. The dissipation of mines, or rather two mines and two rivers, whence •diamonds expofed in coppels was confirmed by M. Mac- diamonds are drawn. The mines are, 1. That of Raolquer ; who further oblerved, that the diamonds were, conda, in the province of Carnatica, five days journey before the dissipation began, rendered, by the fire, from Golconda, and eight from Visapour. It has been brilliant and shining, as it were, with a phosphoric discovered about 200 years. 2. That of Gani, or Coulight. In order to determine whether the diffipation lour, seven days journey from Golconda eastwardly. of diamonds was actually effected by their reduction It was discovered 140 years ago by a peasant, who diginto vapour, or by a combustion or other effect of air ging in the ground found a natural fiaginent of 25 caupon them, Meffrs Lavoitier, Macquer, and Cadet, ex- 3. That of Soumelpour, a large town in the pofed diamon's to intense heat in an earthen retort, kingdom of Bengal, near the Diamond-mine. This during several hours, but without any other effect than is the most ancient of them all : it hould rather be that their polish was destroyed, and about 4th of their called that of Goual, which is the name of the river, in weight diminished. M. Mitouard put diamonds in a the fand whereof these stones are found. Lastly, the tobacco-pipe filled with pounded charcoal and accu- fourth mine, or rather the second river, is that of SucTately closed with lute. He further fecured the dia- cudan, in the island of Borneo. monds from accefs of air or fame, by placing the to- Diamonn-Mine of Raolconda.- In the neighbourbacco-pipe in a crucible, to which another crucible was hood of this mine the earth is fandy, and full of rocks. inverted and carefully luted. The diamonds, thus fe- and copse. In these rocks are found several little cluded from external air, having been exposed to the veins of half and sometimes a whole inch broad, out most intense heat which could be excited in a well con- of which the miners, with a kind of hooked irons, fructed furnace, were not thereby altered or diminish- draw the sand or earth wherein the diamonds are ; ed. M. Mitouard was induced to believe, that the breaking the rocks when the vein terminates, that the charcoal conduced to the preservation of diamords not track may be found again, and continued. When a merely by excluding the air, but by some peculiar pro- fufficient quantity of earth or fand is drawn forth, they perty, which he supposes may be the same as that by wash it two or three times, to separate the itones there
Diamond. from. The miners work quite naked, except for a round with stores, earth, and fascines, and lading ou: Diamnd. brany thin linen cloth before them; and belides this pre- the water, dig about two feet deep: the land thus gut
porod caution, have likewise inspectors, to prevent their con- is carried into a place walled round on the bank of the cealing of stones : which, however, maugre all this river. The rest is performed after the same mamer care, they frequently find means to do, by watching op- as at Coulour, and the workmen are watched with equal portunities when they are not observed, and swallow. ftriétners. ing them down.
Diamond-Mine in the island of Borneo, or river of
the diamonds was always either black or yellow; and
But the Europeans are nut usually daring or export e-
propera diamond points, or sparks, called natural sparks, are ly called a coloured one: for it would be an impropriery brought. They never begin to feek for diamonds in to speak of an imperfectly coloured diamond, or one this river till after the great rains are over, that is, af. that has other defects, as a itone of a bad water only. ter the month of December; and they usually even Mr Boyle has observed, from a person much conwait till the water is grown clear, which is not before versant in diamonds, that some of these
in their January. The season at hand, cight or ten thousand jough state, were much heavier than others of the same persons, of all ages and sexes, come out of Soumel- biguess, especially if they were cloudy or fvul; and pour and the neighbouring villages. The most expe. Mr Boyle mentions one that weighed 8 grains, which rienced among them search and examine the fand of being carefully weighed in water, proved to an equal the river, going up it from Soumelpour to the very bulk of that liquor as 2 to 1.
So that, as far as mountain whence it springs. A great fign that there could be judged by that experiment, a diamond weighs are diamonds in it, is the finding of those stones which not thrice as much as water : and yet, in his table of the Europeans call thunder-ftones. When all the sand specific gravities, that of a diamond is faid to be to of the river, which at that time is very low, has been water as 3400 to 1000; that is, as 3 to 1; and therewell examined, they proceed to take up that where. fore, according to these two accounts, there should be in they judge diamonds likely to be found ; which is some diamonds whose specific gravity differs nearly s done after the following manner : They dain the place from that of others. But this is a much greater dit.