The weight of the standard pound in a vacuum (that is, its weight not diminished by the buoyancy of the air) being 7000 grains, a commercial brass pound exactly equal to the platinum standard when weighed against it in air at 62°, would weigh 7000·6 grains in a vacuum.
This, 1/16 of an ounce = 27-1/3 grains, is principally used as a unit for powder in the cartridges of sporting guns. In Scotland it was called a ‘drop.’
1673. A quech weighing 18 unce and 10 drop.
1805. An arrow of from 20 to 24 drop weight (‘N.E.D.’).
The dram was possibly so called from its corresponding to the quentchen, 1/8 of the German Loth or half-ounce (1/16 of a marc) as the drachm was 1/8 of a medicinal ounce.[24] Or it may merely have been called a dram as being the part of the ounce, in the same way that the drachm was the next lower part of the apothecaries’ ounce.
The dram of spirits is a measure probably so called from its being 1/8 of a pint, i.e. half a quartern.
3. SCIENTIFIC AND MEDICINAL DIVISIONS OF THE POUND
For scientific purposes the pound is considered as of 7000 grains. It may be divided into tenths, hundredths, thousandths; this last division being called a Septem, as = 7 grains. The tenth of this might be called a Septula = 0·7 grain, and the hundredth a Septicent = 0·07 grain. This small weight would be one 100,000th of the gallon, the same proportion as the centigramme to the litre. In analyses of water the solid constituents are usually stated in centigrammes to the litre, or parts in 100,000; and as grains to the gallon or parts in 70,000 they have to be divided by 0·7 to get that ratio. Septicents to the gallon would be the English equivalent of centigrammes to the litre.
An Apothecaries’ Troy ounce lingers in the Board of Trade list of standards, for a permissive use utterly unrequired by medical prescribers or by druggists; the British Pharmacopœia only recognising Imperial weight, the ounce and the grain. For convenience, a weight of 60 grains is called a Drachm, and one of 20 grains is called a Scruple. It is most rare for prescriptions to contain an ounce of any solid medicine; and when an ounce of such a medicine is most exceptionally prescribed, it might be an Imperial ounce, just as ounces of fluid medicines prescribed are Imperial ounces.