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Notes on the weight of the ‘Cullinan’ diamond, and on the value of the carat-weight

Published online by Cambridge University Press:  14 March 2018

L. J. Spencer
L. J. Spencer*
Affiliation:
Mineral Department of the British Museum
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Extract

The history of famous diamonds has always been surrounded with mystery and uncertainty, and this is no less the case with the recently-discovered ‘Cullinan’, by far tile largest of all diamonds, which was found in the Premier diamond mine, near Pretoria, in the Transvaal, on January 25, 1905. Whilst it is now no longer possible to arrive at the exact facts respecting the earlier-found stones, it is desirable to place on record any definite information respecting the more noteworthy stones found in our own time.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 15 , Issue 71 , March 1910 , pp. 318 - 326
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1910

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References

Page 318 note 1 In all these instances the weight is presumably expressed in English carats, but only in tile article in ‘The Times’ of November 10, 1908, is this expressly stated.

Page 320 note 1 This difference between the weighings in Johannesburg and in London is considerably greater than might be accounted for by a correction of the weight of displaced air and the height of the barometer, and, moreover, is in the opposite direction. The stone would weigh more—that is, be less buoyed up—in the more rarefied air of Johannesburg ; the difference (with brass weights) being about 0.014 gram or slightly more than 1/16 carat.

Page 320 note 2 Williams, G. F., ‘The diamond mines of South Africa,’ 1902, p. 520 Google Scholar ; new edition, 1906, vol. ii, p. 160. Here we find the curious statement (copied from Streeter, E. W., ‘The great diamonds of the world,’ 1882, p. 35.Google Scholar) that the carat is ‘equivalent to 4 grains avoirdupois or 3.174 grains troy weight’. Grains avoirdupois and grains troy are, of course, identical. The confusion is no doubt due to the division of the carat into 4 ‘diamond-grains’. We also have the ‘pearl-grain’, 600 of which equal one ounce troy. Such are the pitfalls of the English system of weights and measures !

Page 322 note 1 That is, the weight in air against brass weights. The absolute weight in vacuo would be about 621.33 grams, or about 5/8 carat more.

Page 322 note 2 1 gram = 15.43235 English grains.

Page 322 note 3 Weights and Measures—Report by the Board of Trade on their proceedings and business under the Weights and Measures Act of 1878 ; for 1888, p. 13 ; for 1889, p. 2.

A verbatim reprint of these statements is given by Mr.Vallentine, E. J. in his recent paper, ‘The carat weight.’ Trans. Inst. Mining and Metallurgy, London, 1908, vol. xvii, pp. 430–484 Google Scholar. Unfortunately he gives the equivalent in milligrams as 205.3022 instead of 205.304.

Page 322 note 4 Calculated from 3,0193/4 Dutch carats = 621.20 grams (see above, p. 320).

Page 323 note 1 e.g. from 188.6 mg. in Bologna to 215.99 mg. in Livorno (to quote once more the statements that are copied from one book to another).

Page 323 note 2 This was clearly pointed out by Sir A. H. Church in 1883 (‘Precious Stones,’ 1st edit., p. 50).

Page 323 note 3 The term carat as used to express the fineness of gold, expresses merely a ratio (so many parts in 24), and is now quite distinot from carat-weight. The fact that the Roman siliqua was 1/24 of the golden solidus of Constantine suggests a connexion between these two meanings of the word carat.

Page 323 note 4 Boetius de Boodt, A., ‘Gemmarum et lapidum historia,’ Hanoviae, 1609, p. 65.Google Scholar

Page 323 note 5 Jeffries, D., ‘A treatise on diamonds and pearls,’ London, 1750, p. i.Google Scholar

Page 324 note 1 Mawe, J., ‘A treatise on diamonds and precious stones,’ 2nd edit., London, 1823, p. 2 Google Scholar.

Page 324 note 2 Kelly, P., ‘The Universal Cambist,’ 2nd edit., London, 1835, vol. i, p. 220.Google Scholar

Page 324 note 3 Sir A. H. Church (‘Precious stones,’ 1883, p. 49, and later editions) gives 81/6 grains as the average weight of the seeds of Ceratonia Siliqua.

Page 325 note 1 James Bruce (‘Travels to discover the source of the Nile in the years 1768-73,’ Edinburgh, 1790, vol. v, p. 65 and plate) describes the tree called ‘kuara’, which takes its name from the province of Kuara in Abyssinia, a name that also signifies sun. He mentions that the bean or seed is called carat, and that it is used for weighing gold in Africa and diamonds in India. This is the species Ergthrina tomentosa (R. Brown). Two rather withered seeds of this species, collected in Abyssinia in 1868, I found to weigh 0.106 and 0.119 gram respectively, that is, only slightly over half a carat.

The species E. abyssinie, (mentioned in Professor Max Bauer's ‘Edelsteinkunde,’ 1896, p. 120, 2nd edition, 1909, p. 124, and English translation by L. J. Spencer, 1904, p. 103) is perhaps a synonym of E. tomentosa. For assistance in botanical details I have to thank my colleague Mr. E. G. Baker of the Botanical Department.

Page 325 note 2 Comité international des Poids et Mesures, Procès-verbaux des séances, Paris, 1907, sér. 2, vol. iv, p. 192. (See also 1905, vol. iii, p. 124.)

Page 325 note 3 Quatrième Conférence généralo des Poids et Mesures, Comptes rendus des séances, Paris, 1907, p. 60.

See also C. E. Guillaume, ‘Lea récents progrès du système mètrique.’ Travaux et Mémoires du Bureau international des Poids et Mesures, Paris, 1907, vol. v, pp. 62-66 (‘La réforme du carat.’) of the separately issued reprint, Paris (Gauthier-Villars), 1907. A notice of this appeared in ‘Nature,’ 1908, vol. lxxvii, p. 611.

These recommendations are mentioned in the Weights and Measures Reports (1908, p. 4 ; 1909, p. 4) of the Board of Trade in London ; and also in the paper by E. J. Vallentine quoted above.