“The Committee of the Association approves the attempt to urge the adoption in all countries of an international carat of 200 milligrams, and hopes that, in the interest of the unification of weights, it will prove successful.”
The fourth General Conference of Weights and Measures, held in Paris in October, 1907, passed this resolution:
“The Conference approves the proposition of the International Committee and declares that it sees no infringement of the integrity of the metric system in the adoption of the appellation ‘metric carat’ to designate a weight of 200 milligrams for the commerce in diamonds, pearls, and precious stones.”[[379]]
The following resolution was passed by The Birmingham Jewelers’ and Silversmiths’ Association, January 23, 1908: “That the best thanks of this Committee be conveyed to the Decimal Association for the good work they are doing, and this Committee expresses the hope that all countries will adopt an International Carat of 200 milligrams in weight.” Finally, on March 11, 1908, the metric carat of 200 milligrams was adopted in Spain as the official carat for diamonds, pearls, and precious stones.
Pearls have become of so much importance to so many dealers that a special form of weight has been proposed for them. This would have a diamond form and not a square form, and it would be stamped “Grain” instead of “Carat.” Another set would be stamped in milligrams, the regular milligram weight with the pearl fraction above it, and they could even be made round so as better to designate the pearl.
The great value of pearls has suggested the making of a gage, called the Kunz gage, by means of which round pearls can be very accurately measured. Pearls of a given weight and perfectly spherical form have been weighed and then measured by this gage, and the theoretical diameters as computed from the measurement of a single pearl are in the majority of instances in exact accord with these actual measurements, the occasional variations in the smaller pearls barely exceeding the thousandth part of an inch. These discrepancies may be due to imperceptible divergencies in sphericity or, possibly, to trifling differences in specific gravity.
The following table gives the diameters of round pearls by measurement, from 1⁄16 to 500 grains, in millimeters and inches:
| Weight Grains | Diameter Millimeters | Inches |
|---|---|---|
| 1⁄16 | 1.3 | .0512 |
| ⅛ | 1.66 | .0653 |
| ¼ | 2.09 | .0823 |
| ½ | 2.65 | .1043 |
| ¾ | 2.99 | .1187 |
| 1 | 3.32 | .1307 |
| 1¼ | 3.60 | .1417 |
| 1½ | 3.80 | .1496 |
| 1¾ | 3.98 | .1567 |
| 2 | 4.18 | .1645 |
| 2¼ | 4.32 | .1701 |
| 2½ | 4.47 | .1759 |
| 2¾ | 4.63 | .1823 |
| 3 | 4.80 | .1889 |
| 3¼ | 4.88 | .1921 |
| 3½ | 5.01 | .1972 |
| 3¾ | 5.17 | .2035 |
| 4 | 5.23 | .2058 |
| 4¼ | 5.44 | .2141 |
| 5 | 5.65 | .2224 |
| 5½ | 5.86 | .2283 |
| 6 | 6.03 | .2374 |
| 6½ | 6.20 | .2442 |
| 7 | 6.36 | .2504 |
| 8 | 6.64 | .2614 |
| 9 | 6.90 | .2716 |
| 10 | 7.15 | .2815 |
| 11 | 7.38 | .2905 |
| 12 | 7.60 | .2992 |
| 13 | 7.81 | .3074 |
| 14 | 8.00 | .3149 |
| 15 | 8.18 | .3220 |
| 16 | 8.36 | .3291 |
| 17 | 8.53 | .3358 |
| 18 | 8.70 | .3425 |
| 19 | 8.86 | .3488 |
| 20 | 9.01 | .3547 |
| 25 | 9.71 | .3823 |
| 30 | 10.31 | .4059 |
| 35 | 10.86 | .4275 |
| 40 | 11.35 | .4468 |
| 45 | 11.82 | .4653 |
| 50 | 12.23 | .4815 |
| 60 | 13.00 | .5118 |
| 70 | 13.38 | .5386 |
| 80 | 14.30 | .5630 |
| 90 | 14.89 | .5862 |
| 100 | 15.42 | .6071 |
| 125 | 16.60 | .6535 |
| 150 | 17.63 | .6941 |
| 200 | 19.41 | .7641 |
| 300 | 22.22 | .8748 |
| 400 | 24.46 | .9630 |
| 500 | 26.35 | 1.0374 |
The new and finer analytical balances weigh to the tenth part of a milligram, the two thousandth part of a carat, the five hundredth part of a grain; but this is not necessary. If the 200–milligram carat were used, the two hundredth part of a carat could readily be ascertained, and then a short-beam, rapid-weighing balance would answer every purpose and save much time for the dealer who must make many weighings in the course of a day. In an office where thousands of weighings were made in a month, the task was accomplished with such minute accuracy that the margin of error did not exceed one carat during that time.
The mina, the sixtieth part of the lesser Alexandrian talent of silver, was divided by the Romans, when they occupied Egypt, into twelve ounces (unciae), and, weighing as it did 5460 grains, it became the predecessor of the European pounds of which the troy pound is a type. If we may believe a Syrian authority, Anania of Shiraz, who wrote in the sixth century, the carat or diamond weight was originally formed from one of these ounces by taking the 1⁄144 part.[[380]]