Until the Pharmacopoeia of 1890 appeared, the weights used in compounding drugs were from the Troy pound, and the measures from the wine gallon. These are still largely, indeed, chiefly used. The edition of the Pharmacopoeia of 1890 adopted the metric system, and hence it is necessary for the prescriber to be familiar with both.

Certain symbols are employed in representing weights :

The pound is represented by........" libra "          (Њ).

The ounce......................."uncia "         ( oz ).

The drachm......................" drachma " ( 3 ).

The scruple......................"scrupulum" (3).

The grain........................" granum " (gr.).

The measures of quantity from the wine gallon are also represented by certain symbols, as follows :

The gallon is represented by..... " congius "          (C).

The pint...................... "octarius"         (O).

The fluid ounce................ " fluiduncia " (f oz ).

The fluid drachm............... " fluidrachma " (f 3 )·

The minim.................... " minimum " (τη,).

The letter "f " is placed before the symbols for ounce and drachm respectively.

The domestic measures are nearly as given below :

A teaspoon contains about............... 1 drachm.

A dessertspoon "         " ............... 2 drachms.

A tablespoon "         " ............... 4 "

A wineglass "         " ............... 2 fluid ounces.

Usually the measures of weight are used to represent quantity as well. In that case the same symbols may represent both. In prescribing liquids the letter " f " is generally made to precede the symbol, for the reason that some liquids weigh more, others less, than the indicated quantity.