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fen out of a large parcel, each as different from the other as could be, in fhape, colour, and whatever other reipe&s might make a change; thefe being weighed in the fame fcales and water as the former, the lighteft proved to be as 3512, and the heavieft as 3525 to 1000, in proportion to water. The very near agreement of thefe Lift with one another, and with the former two, weighed at a di fiance of time, makes it highly improbable there fhould be fo great a difference as that expreffed in Mr. Boyle's tables, in any Diamonds whatever, much lefs fo great a difference as appears between the lighteft of his, and the heavieft of thefe, being above one feventh of the whole. It is very certain that there may be fome difference in thefe trials from the nature and temper of the water ufed in the ex- periments; fome waters, as that of pumps or wells, being heavier than rain or diftilled water, and the heat or coldnefs of the water may alio make fome variation: this, however, is much lefs than might be expected; careful experiments hav- ing proved, that the fpecific gravity of any body will not dif- fer above —r at moil, on account of the difference of the water in quality and temper taken together; whereas the hea- vieft and lighteft of the Diamonds in Mr. Bovle's and thefe experiments differ about one thirty-fifth part,' which is about fix times as much as ^\s.
Mr. Ellicot, who made thefe experiments, has drawn out a tabic of their feveral differences, which is done with great care and accuracy, and taking in all the common varieties in Diamonds, may ferve as a general rule of their mean gravity and differences.
Water — — _ N° 1. A Brazil Diamond, fine water, and rough coat _
2. Ditto, fine water, rough coat
3. Ditto, fine bright coat
4. Ditto, fine bright coat ■
5. An Eaft-India' Diamond, pale
blue — — —
6 Ditto, bright yellow — —
7 Ditto, very fine water, bright
coat — — • — 1
8 Ditto, very bad water, honey-
comb coat — — — g Ditto, very hard, blueifh caft
10 Ditto, very foft, good water
11 Ditto, a large red foulnefs in it
12 Ditto, foft, bad water — —
13 Ditto, foft, brown coat- ■
14 Ditto, very deep green coat —
In air.
la water.
Spe
ific
Grains
Grains
gray
ty.
92,425 66,16 3518
88,21 63,16 3521
10,025 7,170 3511
9,560 6,830 3501
35" 3524
26,485
18,945
■ 23.33
16,71
20,66
i 4l 8
• 20,38
14.59
22,5
16,1
22,615
16,2
25,48
18,23
29.525
21,140
26,535
18,99
25.25
18,08
3525
35 *9 35 J 5 35 2 5 35 l A 352i 35!° 352i
The mean fpecific gravity of the Brazil Diamonds
appears to be
The mean of the Eaft-India Diamonds - The mean of both — —
Therefore, if any thing determinate is to be faid, as to the fpecific gravity of the Diamond it is, that it is to water as 3517 to 1000. Phtlof. Tranf. N P 4y6. p. 472.
Valuation of Diamonds — Mr. Jeffries lays down the following rule for the valuation of Dia?nonds of all weights. He firft fuppofes the value of a rough Diamond to be fettled at 2 I. per carrat, at a medium; then to find the value of Diamonds of greater weights, multiply the fquare of their weight by 2, and the product is the value required. E. G. to find "the value of a rough Diamond of two carrats, 2x2=4, the fquare of the weight, which multiplied by 2, gives 8 I. the true value of a rough Diamond of two carrats. For finding the value of manufactured Diamonds, he fuppofes half their weight to be loft in the manufacturing them; and therefore to find their value, wc muft multiply the fquare of double their weight by 2, which will give their true value in pounds: thus, to find the value of a wrought Diamond weighing two carrats; we firft find the fquare of double the weight, viz. 4x4—16, then 16x2=32. So that the true value of a manufactured Dia- mond of two carrats is 32 1.
By this rule Mr. Jeffries has conftructed tables of the price of Diamonds from I to 100 carrats. Jeffries on Diamonds, p. 8, 9. & p. 11. feq. of his tables.
Rough Diamonds are more commonly found of a fix pointed figure than of jny other; and thefe are called fix -pointed rough Diamonds, the figure of which is compofed of two fquare pyramids, joined at their bafes. Hence the whole figure is compofed of eight triangular faces, or planes, four of which meet in a point above the bafe, and four below it, in another point.
The diftance of thefe two points is the axis of the fi- gure.
Dimcnfions of a fquare brilliant Diamond.— To make a complete fquare Brilliant, if the rough Diamond be not found to be of the figure here defcribed, it muft be made fo. And if the Suppl. Vol. I.
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work be perfealy executed, the length of the axis will ht equal to the fide of the fquare bafe of the pyramid. Jewelers then form the table and collet, by dividing the block or length of the axis into 1 8 parts. They take ,V from the upper part, and -,'t from the lower. This gives a plane at -4,- diftance from the girdle for the table; and a fmaller plane at T! T diftance, for the collet; the breadth of which will be f of the breadth of the table. In this ftate the ftone « faid to be, a complete fquare table Diamond. Jeffries on
Diamonds,
P- '3-
The Bniiiant is an improvement on the table Diamond, and was introduced within the laft century, according to Mr. Jef- fries.
To lender a Brilliant perfect, each corner of the above de- fenbed table Diamond, muft be ihortened by T ' T of itsdiagonal. The corner ribs of the upper fides muft be flattened, or run towards the center of the table £ lefs than the fides. The lower part which terminates in the girdle, muft be 4. of one fide of the girdle; and each corner rib of the under fides muft be flattened at the top, to anfwer the above flattening at the girdle, and at bottom muft be i of each fide of the collet. The parts of the fmall work which completes the brilliant, or the (far and skill facets, are of a triangular figure. Both of thefe partake equally of the depth of the upper fides from the table to the girdle, and meet in the middle of each fide of the table and girdle, as alfo at the corners. Thus they pro- duce regular lozenges on the four upper fides and corners of the ftone. The triangular facets, on the under fides, joining to the girdle, muft be half as deep again as the above facets to anfwer to the collet part.
The ftone here defcribed is faid to be a full fubjlamed Brilliant. If the ftone be thicker than in the proportion here mentioned, it is faid to be an over-weighted Brilliant. If the thicknefs be lefs than in this due proportion, it is called zfpread Brilliant.
The beauty of Brilliants is diminiftied by their being either over-weighted or fpread. The true proportion of the axis or depth of the ftone to its fide, is as 2 to 3. Brilliants are diftinguiftied into fquare, round, oval, and drops, from the figure of their refpecf ive girdles.
Dimenfwns of a rofe Diamond— In rofe Diamonds the depth of the ftone from the bafe to the point, muft be half the breadth of the diameter of the bafe of the ftone. The diameter of the crown muft be j of the diameter of the bafe. The perpendi- cular from the bafe to the crown muft be f of the depth of the ftone. The lozenges, which appear in all circular rofe Dia- monds, will be equally divided, by the ribs that form the crown; and the upper angles, or facets, will terminate in the extreme point of the ftone, and the lower in the bafe or girdle.
The tafte winch now prevails of converting rofe Diamonds into Brilliants, is condemned by Mr. Jeffries; unlefs the rofe Diamonds be over-weighted. He thinks, that the dif- play of beauty, in rofe Diamonds, is often preferable to that of Brilliants. See his treatife on Diamonds, p. 32, 35. Mr. Jeffreys's table of the value of Diamonds differs confider- ably from that in the Cyclopsedia. This not following the rule laid down by him, of the values increafing in the duplicate proportion of the weights.
Complexions of Diamonds — The fineft Diamonds are thofe of a complexion like that of a drop of the cleareft rock water : and if fuch ftones be of a regular form, and truly made; as alfo free from ftains, fouls, fpots, fpecks, flaws, and crofs veins, they will have the higheft luftre of any, and be efteemed the moft perfect.
If Diamonds be tinflured yellow, blue, green, or red, in a high degree, they are next in efteem. But if they partake of thefe colours only in a low degree, it greatly finks their value. There are other complexions of Diamonds, fuch as the brown, and thofe of a dark hue; the firft fometimes refemble the browned fugar-candy, and the latter dusky-iron. The firjl water in Diamonds means the greateft purity and perfection of their complexion, which ought to be that of the cleareft drop of water.
When Diamonds fall fhortV this perfection, they are faid to be of the fecondov third water, &c. till the ftone may be pro- perly called a coloured one : for it would be an impropriety to fpeak of a Diamond imperfectly coloured, or having other defects, as a ftone of ihad water only.
Magnitude of Diamonds — The moft remarkable Diamonds for fize now known, are, Governor Pitt's Diamond, purchafed by the late Duke of Orleans for Louis the XVth King of France, weighing 136-!- carrats : the Diamond of the Great Duke of Tufcany, which weighs 139 * carrats: that of the Great Mogul, weighing 279 -^ carrats : and one, mentioned by Mr. Jeffries, in a merchant's hands, weighing 242 7^ carrats.
According to Mr. Jeftries's Rule, that the value of Diamonds is in the duplicate ratio of their weights, and that a manu- factured Diamond of 1 carrat is worth at a medium 8 1. the Great Mogul's Diamond muft be valued at above 624962 1. this being the value of a Diamond of 279 J carrats.
9 E Cormjh
