seeds of
Abrus precatorius L.

Hard red seeds with a black spot, widely used as an informal weight standard. Like almost all plant species whose seeds have been used as a standard of mass, Abrus has highly consistent side-to seed weights, at approximately 10 seeds to a gram. The seed's weight also does not change very much over time. They are highly toxic. The plant, a tropical vine, is found throughout the warmer areas of the world, having been introduced in many places as an ornamental. It has many common names: jequerity, precatory bean, rosary pea and others. In the United States, the seeds are called crab's eyes in North Carolina, and lady bug seed in California. Consult the Web sites listed at the end of this page for pictures of the plant, and its other names and non-metrological uses.

Language or area Name of seed Name of unit, if different
Fezzan ain el deek (cock's eye)  
Timbuktu, Djenné, Bonduku damma  
Akan (West Africa) damma or damba  

sources

1

A sample of 200 Abrus seeds from southern Ghana had an average weight of 0.074 grams, determined by an electric precision balance. The seeds varied between 0.068 and 0.079 grams but when used in groups of half a dozen or more gave an average of around 0.074 grams.  Their weight remained almost constant over a period of several months.

Garrard (1980, page 232)

2

The small weight, commonly called goldsmith's weight, is either founded on the goonj or ruttee, or the mustard seed. The goonj or ruttee is the small red seed, whether of the white or red species, of the abrus precatorius; these seeds are very uniform in size, and the plant producing them grows wild all over India. Two seeds, otherwise goonj, make one waal, a weight represented by a seed of the Cheelur. This weight is further subdivided as follows:—two barley corns—1 goonj and eight mustard seeds—one barley corn,--under different governments of India the total is composed of different proportions of the goonj, or of the mossa [sic]. The Bengal tola being of 100 goonj, or 12½ massa; the Malwa tola of 96 goonj or 120 massa. The Bombay tola of 92 goonj or 11½ massa. Several districts in the Southern Concon of 92 goonj, or 11½ massa; 90 goonj, or 11¼ massa; and 96 goonj, or 1 [sic but probably a misprint for 120-ed.] massa. The pice of Kota in Malwa is equal in weight to 80 massa, so that from these we may hope ot obtain something approaching to the common weight of the massa or goonj, the fundamental measures of weight.

The weight of the Bengal massa, in troy grains, is 15,353, being 191,916 troy grains, the weight of a Calcutta sicca rupee, divided by 125, the number of massa in one tola. The weight in troy grains of the tola in Malwa is 190 grains; which being divided by 12, (the number of massa in 1 tola,) gives 15,8333 troy grains for the weight of the massa.

In ascertaining (says Major Sykes) the weight troy of a goonj with a hydrostatic balance, turning with the tenth of a grain, the result was as follows;—32 seeds of goonj, weighed 605 [sic, misprint for 60.5] grains troy; 16 seeds or goonj, weighed 305 [sic, misprint for 30.5] grains; 8 weighed 15.1; and 56 seeds weighed 1052 [sic, misprint for 105.2] grains, which would give an average weight of 1,914 grains for each seed; 96 of these would make the tola equal to 183,7636 grains troy. But as the seer weight of 80 rupees, 13,800 grains troy, is to consist of 72 tolas, the tola should weigh 191,6666 grains, instead of 183,7536, affording sufficient evidence that the tola in use, like every other weight, is below the proper standard.

Robert Montgomery Martin.
History of the Colonies of the British Empire…
London: Wm. H. Allen and Co. and George Routledge, 1843.
Page 143, Appendix IV.

Aside from the obvious misprints, the arithmetic is wrong. No combination of the data given gives an average of 1.914. Both the individual sets, and the data taken as a whole, give averages of about 0.122 gram per seed.

Resources

See:

www.ansci.cornell.edu/plants/rosarypea.html
www.rain-tree.com/abrus.htm

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