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.